- Email: [email protected]
Lighting systems in major New Zealand controlled environment facilities
J. agric. Engng Res. (1978) 23, 23-36
Lighting
Systems
in Major New Zealand
Environment
Controlled
Facilities
I. J. WARRINGTON* ; T. DIXON* ; R. W.
ROBOTIIAM*
; D. A. ROOK?
The lighting systems used in New Zealand in the Department of Scientific and Industrial Research (DSIR) Climate Laboratory controlled environment rooms, the Forest Research Institute (FRI) tree growth rooms, and the DSIR-designed reach-in controlled environment chambers are described. All lighting systems are based on high-pressure discharge lamps which can be used with varying amounts of incandescent light supplementation. The main lighting type used in the Climate Laboratory controlled environment rooms is the high-pressure metal
halide lamp, that in the FRI rooms the high-pressure mercury-vapour fluorescent lamp with internal reflector, and that in the reach-in chambers a high-pressure mercury halide lamp. Details of lighting rig design, of irradiance levels obtainable, vertical and horizontal light distribution patterns and spectral quality are presented for each system. The photosynthetic irradiancelevels available at 2-3 m below the lighting systems in all of these controlled environment systems are high (180-200 W m-a PAR). In the Climate Laboratory and FRI growth rooms peak sunlight values of approximately 400 W m-a PAR (approximately 10,000 ft.c.) have been achieved. A discussion of the performance of these systems is also presented.
1. Introduction A major area of interest in controlled environment biology is the supply of light to plant growth chambers where daylight is completely excluded. Lamp systems used in these situations should simulate daylight as closely as possible. Consequently design features should take account of plant requirements for photosynthesis, for photomorphogenesis and for photoperiodism. Hence the system should (1) provide an adequate photosynthetic photon flux density (PPFD)’ in the photosynthetically active range (PAR), 400-700 nm, (2) have a satisfactory spectral energy distribution in the photosynthetically active and near infra-red wavebands. and (3) provide control over the duration of lighting. In addition, it may be useful to have the capacity, in an artificial lighting system, to change the irradiance at different times of the day (i.e. provide stepped lighting programmes compared with the usual square-wave programme?) and to change the spectral energy distribution during the course of the day in a similar manner to natural daylight changes. In practice few of these requirements are completely satisfied m controlled environment lighting systems and insufficient experimentation has been undertaken to characterize the nature and magnitude of the design inadequacies that may exist. The majority of both reach-in and walk-in controlled environment (CE) chambers constructed and operated through the 1950 to 1970 period used fluorescent-lamp based systems supplemented with various proportions of incandescent lighting 3- ‘O. Details of vertical and horizontal light distribution patterns within these CE chambers, maximum irradiance levels achieved and information on lamp ageing characteristics have been presented by Carpenter and Moulsley’, Downs and coworkers** 9 and Kalbfleisch’O for a range of facilities in different countries. In general, fluorescent-lamp based systems produce photosynthetic photon flux densities (PPFD) of approximately 650 to 750 microeinsteins m --2 s-r (i.e. equivalent to less than half of full sunlight values), result in a very even distribution of light energy across the plant growing platform with some decline around the edges, but have undesirable ageing characteristics (i.e. approximately 20 to 25 ‘A decline in light output after 4000 h or 1 year of operation).’ The main *Climate Laboratory, Plant Physiology Division, D.S.I.R., Palmerston North, New Zealand tForest Research Institute, New Zealand Forest Service, Rotorua, New Zealand Received 16 May 1977; accepted in revised form 4 July 1977 23
24
LIGHTING
SYSTEMS
technical advantage of these systems is that they have a low heat output, and although adequate ventilation must be assured for the maintenance of proper lamp operating temperatures,B generally only a simple barrier of transparent plastic or plate glass is required between the lamps and the plant growth chamber. In recent years, high-pressure discharge lamps have been extensively used in CE units of various sizes from reach-in chambers to walk-in rooms. Although plants perform and grow well under these lamps” -13 there are no published data on the physical design or performance of highpressure discharge lamp-based lighting systems. In this paper we describe the systems used in the New Zealand Department of Scientific and Industrial Research (DSIR) Climate Laboratory rooms, the NZ Forest Service Forest Research Institute (FRI) tree growth rooms and the DSIRdesigned reach-in CE chambers. Air out
I@\-
,
-
r--x== ----
El.00
Airout2
-
r
Fig. I. Cross-sectiondiagrams of ClimateLoboratory CE room (left) and FRI tree growth room (right). ANdimensions are in metres. A, lamp loft; B, movable lighting rig; C, lamp ballast and control equipment; D, thermal barrier; E, plant growth chamber; F, side and rear wallmirrors; G, reflective whiteinterior walls; H, plant growth trolleys at standard height: I, slottedjloor; J, reflective aluminium-foil wall-liner: K, movable floor; L, plant root containers
2. Controlled environment facilities 2.1.
General
The general features of the Climate Laboratory CE rooms’ 4 and those of the FRI tree growth rooms15 have been described elsewhere. A cross-section diagram of each design is shown in Fig. I. The DSIR-designed reach-in cabinet (made under license by Temperzone Ltd, Auckland, N.Z.) is a small version of the Climate Laboratory CE room; the plant growth chamber measures 1.2 x 0.9 x I.8 m high.
I. J.
WARRINGTON
El-
AL.
25
All of the lighting rig/lamp loft configurations described for these systems have been designed to permit the joint use of high pressure discharge lamps, which provide the high photosynthetic photon flux densities desirable for plant growth, and quartz halogen or incandescent lamps, which provide photoperiodic lighting as well as the supplementary red and far-red light necessary for photomorphogenesis and photosynthesis. Hence the combined use of 2 lamp types results in a balanced visible and far-red spectrum necessary for normal plant growth and development. High plant growth-chamber temperatures have been minimized by the combined use of thermal barriers and high rates of lamp loft ventilation. Unlike many of the fluorescent lamp based systems in use, the systems described allow easy lamp access even during plant growth-chamber operation. The size and accessibility of the lamp lofts and lighting rigs also allow the addition or replacement of new lamp types as advances in lighting technology produce improved lamps.
Fig. 2. Climate Laboratory CE room. A stanaiwdlighting rig in the operuting position above a CE room. Fluted reflectors house the high-pressure discharge lamps. Lamp control gear is readily accessible on the top of the rig. The portable lighting rig frame is easily removed from above the room for repairs and maintenance
2.2. DSlR Climate Laboratory Lamps are mounted on a movable frame in the lamp loft above each plant growth chamber (Figs 2 and 3). The frame measures 2.70 x 1.80x I.10 m high and straddles the 3.00 x 1.60 m plate glass-water thermal barrier. The loft measures 3.20 x 2.40 x 1.90 m high and is air cooled to maintain a temperature of approximately 30°C. Electricity is supplied to the rig by 4 flexible, trailing cables (&phase, 70 A capacity per phase) which connect to junctions for the high-pressure discharge lamp ballast and control gear, or for direct supply to the quartz halogen and incandescent lamps. The high-pressure discharge lamp ballast and control gear are mounted directly on the lamp rig and are air cooled with the lamps. All ballast and lamp types tested in the Laboratory to date have been mounted on the rig in this way. Individual wiring systems are employed to allow separate timing of the main photosynthetic lighting system and of the smaller incandescent photoperiod lamps. The electrical supply is voltage controlled to f2% and constant-voltage ballasts are used to ensure stable light output from the high-pressure discharge lamps. In the event of a power failure, a standby diesel-fueled power supply allows the operation of the photoperiod lights in all CE rooms and of the main photosynthetic lights in selected CE rooms. Horizontal and vertical placement of the lamp and reflector assemblies is achieved simply by mounting the lamp holders on horizontal beams at
26
LIGHTING
SYSTEMS
different heights across the lighting rig. The faces of all reflectors are adjusted to be 10 cm from the plate glass-water thermal barrier. The lamp and reflector-assembly angle can be adjusted from a simple swivel-mount at each reflector base. Each lamp rig can be withdrawn from the lamp loft for checking light operation, for maintenance, or for reconstruction using different lamp types. The standard lighting combination comprises 4 x 1000 W “Metalarc” high-pressure metal halide lamps (Ml000 BU Sylvania) and 4 x 1000 W quartz halogen lamps (Philips type 12012 R). A high irradiance system was also tested; this comprised 6 x 1500 W “Metalarc” high-pressure metal halide lamps (M 1500 BU Sylvania) and 8 x 1000 W quartz halogen lamps. The reflectors used for the high-pressure discharge lamps were the Duraglow (General Electric Co.) type, and for the quartz halogen type the Philips reflector housing NK 17/00. On all lamp rigs, 6 x 150 W incandescent lamps (Mazda reflected flood) are used to provide low irradiance photoperiodic lighting.
Fig. 3. Climate Laboratory CE room. View of part of a standard lighting rig in operating position above the plateglass-water thermal barrier. Mirrored wallpanels produce multiple images. Air inlet grills along each side of the room are also shown
The plant growth chamber is separated from the lamp loft by a thermal barrier comprising a single sheet of 8 mm plate glass supporting a 3.5 cm deep water layer. The water flow rate is 16-18 1 min-l. Water temperature is controlled to be similar to the plant growth chamber temperature in order to avoid condensation at the glass-air interface. The thermal-barrier water is within a closed system; in which either warm water is supplied to the barrier from a small adjacent tank (1 kW heating element) that forms part of a secondary circulation system, or cold water is supplied from the central holding tank directly to the thermal barrier. Water leaving the barrier returns to the central holding tank where cooling, filtration and algicide injection occurs. Each barrier is cleaned twice a week with a vacuum line to remove dead algae and accumulated dirt particles. To improve light distribution within the plant growth chamber, mirrors are surface mounted to the walls and air ducting systems and extend from plant growing height to the underside of the plate glass-water thermal barrier.
I. J.
WARRINGTON
ET
27
AL.
Fig. 4. FRI tree growth rooms. View of lighting rig with one of its air inlets as seen from within the controlled environment room through the glass screen. The aluminium foil liner has been fitted and the air inlet grille and part of the support structure for the movable steel floor are also shown
2.3.
FRI tree growth room.,
Each 3.3 x 3.3 m welded steel lamp rig can accommodate 162 x 400 W high-pressure mercuryvapour lamps with internal reflectors (Philips HPLR-N) and 162 x 150 W low heat output incandescent lamps (Philips Attralux PAR38). The incandescent and mercury-vapour lamps are evenly distributed throughout the lighting rig (Figs 4 and 5) and each lamp type is arranged on a separate timing system. In the tests reported here however, only 119 incandescent lamps were used with 162 mercury vapour lamps. The incandescent lamps provide photoperiodic lighting as
Fig. 5. FRI tree growth rooms. View of lighting rig on its overhead rail svstem. The ventilated cabinets housing the lamp control equipment and ballasts are on the right of the figure
28
LIGHTING
SYSTEMS
well as the supplementary red and far-red light necessary for photomorphogenesis and photosynthesis. All lamps are cooled by filtered air (340 m3 min-l) which enters from opposite sides of the loft and is vented via a jet fan positioned above the centre of the lamp rig. A screen of heat-toughened plate glass, 6.4 mm thick, and sub-divided into 12 sections, each 0.9 x 1.2 m, is supported on a steel frame which separates the growing space from the lighting system. No water thermal barrier is used.
Fig, 6. Reach-in cabinet. A lighting rig in the servicing position on the overhead rails outside of the cabinet. Mirrored wall panels and air outlet grills are shown within the plant growth chamber
Each lamp rig can be withdrawn from the 3.7 x 3.7 x 1.4 m high lamp loft on an overhead rail system for checking light operation, for maintenance, or for reconstruction using different lighting units. Power is supplied to each rig by ten trailing cables. The lamps can be manually switched off in pairs thus allowing a range of irradiance levels and distributions of light to be provided. In the event of a power failure, a standby diesel-fueled power supply allows 24 incandescent lamps in each rig to be operated. The ballasts for the high-pressure discharge lamps are mounted separately from the main lighting rig, on thick aluminium plates in cabinets which are fitted with individual air circulation/ ventilation systems for heat dissipation. To improve light distribution across the tree growth chamber each wall is lined with heavyduty aluminium foil to increase reflectance. Outlets have been provided for the installation of up to 8 kW of lighting laterally within the chamber.
I.
J. WARRINGTON
ET
29
AL.
2.4.
Reach-in cabinet
The lamp fittings are mounted directly on a sheet of heat-resistant material (“Formica”) which is suspended from an overhead dual railing system. The 2.73 x 1.02 x0.70 m high lamp loft is air-cooled with a 40-cm fan which draws filtered air through the system. The lighting combination used in the tests comprised 6 x 375 W high-pressure mercury halide lamps (Philips HPI/T in Philips HGH 375 reflector fittings) and 2 x 1000 W quartz halogen lamps (Philips type 12012R in Philips QGH 1000 reflector fittings). In addition, 3 x 100 W incandescent (Philips inside-frosted) lamps were installed for photoperiod lighting @g,s 6 and 7). Ballast and control equipment for the lamps are mounted in a separate, ventilated cabinet on the outside of the plant growth chamber. The plate glass-water thermal barrier is similar in performance and design to that in the Climate Laboratory CI rooms. All internal walls of the plant growth chamber are lined with 8 mm plate-glass mirror,.
Fig. 7. Reach-in cabinet, Plan view of cabinet lighting rig. Both the high pressure discharge (old1 ,side rows) and quartz hak rgen lamps (central Ipow) are housed in similar reflectors. Three low-irrtensity photope?riod extension lamps are spaced along the centre of the rig
3. Measurement instrumentation and technique Light uniformity was measured at set distances from the thermal barriers over a horizontal grid system using an EEL photometer without a fitted cosine-corrected head (Evans Electroselenium Ltd, Essex, England). Measured values were used to determ:ne coefficients of variation of the light distribution. The spectral distribution of each lighting system was measured with an ISCO spectroradiometer and record-scanner (Instrumentation Specialities Co., Lincoln, Nebraska, U.S.A.). Total and photosynthetic energy flux densities were recorded using an Eppley pyranometer (Eppley Lab., Newport, U.S.A.) plus a Schott RG8 (Schott and Gen., Mainz, W. Germany) filter system. Values are presented for 380-700 (photosynthetically active radiation, PAR), 700-1400 and 380-1400 nm wavebands where a plate glass-water thermal barrier was used16, or as 380-700, 700-2500 and 380-2500 nm wavebands where a plateglass thermal barrier was used.
30
LIGHTING
h&IkP
87
-0-45
SYSTEMS
87
mI.80
m
Fig. 8. Relative light meter values recorded with an EEL photometer, on a I.8 x 1.8 m horizontal grid 2 m from the thermal barrier in a Climate Laboratory CE room (standard lighting rig). Underlined values represent PPFD and energy flux density measurement locations
Photosynthetic photon flux density (PPFD) was measured with a Lambda quantum sensor (Lambda Instruments Corp., Lincoln, Nebraska, U.S.A., meter LI 185, sensor S/N Q152/725). The spectral distribution, and energy and PPFD values presented are means of measurements recorded at several places on the horizontal grid systems. 4. Performance of lamp systems 4.1. Climate Laboratory CE rooms A typical light distribution pattern for values recorded on a 1a8x l-8 m square grid (O-45 m squares) across a horizontal plane at normal plant container height, 2 m from the thermal barrier, is shown in Fig. 8. At 1.5 m from the thermal barrier the coefficient of variation was 12 ‘X and at 2.5 m, 3%. it short distances from the thermal barrier, irradiance levels declined towards the side walls (Fig. 9). I
0.0
0.5
“_
I.0 Oktome
ocmss
grid
(m
1
Fig. 9. Light distribution at various distances from the thermal barrier in a Climate Laboratory CE room. Top, 1.18 m; middle, 2.00 m; bottom, 2.9 m. M, Centre front to centre rear: O---O, centre side to centre side (standard lighting rig)
I. J.
WARRINGTON
ET
31
AL. TABLE I
Climate L&oratory CE room: radiant energy ffux density and quantum flux density values at standard plant container height (means of 5 readings) Standard
___-
Light system
Eppley (400-1400 nm, W m-*) Eppley/RGI filter (400-700 nm, W m- *) Eppley/RGI filter (700-1400 rim, W mv2) Quantum sensor (400-700 Ml) (pE md2 s-l)
High irradiance rig*
lighting rig* Quart.: iodide ___-
All
Metal-arc
All
206
150
51
485
154
137
20
365
52
13
31
120
632
552
94
1665
*After 2000 h operation
I
55-%-T+-
0.4
0.8
I.2
I.6
Distance from thermal
Fig. 10. PAR
horizontal
8.0
2-O
2.4
barrier
2.8
(m )
fluxes at various distances from the thermal barrrer. Top, FRZ tree growth Climate Laboratory CE room. a, Quantum flux; o, PAR energy flux
room; bottom,
32
LIGHTING TABLE
SYSTEMS
II
FRI tree growth room: radiant energy flux density and qaantmn flax density values at several measurement heights (means of 6 readings)* Light system Distance from thermal barrier, m
~__ Eppley (400-2500 nm, W mm2) Eppley/RGI filter (400-700 nm, W me2) Epply/RGS filter (700-2500 nm, W m- *) Quantum sensor (400-700 Ml) (pE m-2 s-l )
2
4
6
8
841
624
488
372
386
386
289
223
167
455
335
265
1620
1227
903
4
6
296
240
192
248
189
52
41
205
138
107
188
151
702
997
763
231
189
-
416
-
*After 2OW h operation
Z-
‘E c
“: E
I.6 1*4-
2
;:;_
.‘; ;
0*8-
+ 2
0.6 0.4 0.2 -
/v I
Lx. $ 15 I.8 I.6 I.4 I.2
I
I
I
-
d:; 0.6 0.4 o-2 :L& 400
500
600
Wavelength
(nm)
700
Fig. II. Spectral energy distribution for each lighting system. Top, Climate Laboratory CE room: centre, FRI tree growth room; bottom, reach-in cabinet
I. J. WARRINGTON
33
ET AL.
Total energy flux, photosynthetic irradiance (PI) and PPFD values for both the standard and high irradiance lamp combinations are shown in Table I. Photosynthetic irradiance (PI) declined curvilinearly over the normal plant growing height interval (i.e. 1.2 to 2.6 m below the thermal barrier); the rate was approximately 70 W m-2 m-l (Fig. 10). The spectral distribution of the lamp combination tested is shown in Fig. 11. 4.2. FRI tree growth rooms Light distribution patterns were recorded on a horizontal grid (060 m squares) at several distances from the thermal barrier. The coefficients of variation were 7, 10, 8 and 7 % at 2, 4, 6 and 8 m, respectively, from the barrier. As in the Climate Laboratory CE rooms, these values confirm the even nature of light distribution across the plant growing area; a decline in irradiance was recorded around the outer limit of the measurement grid but these values were not included in the coefficient of variation calculations as the measurements were outside of the normal plant growing area. Total energy flux, PI and PPFD values are presented in Table II for several measurement heights. PI declined curvilinearly (approximately 35 W m -2 m - ‘) as the distance from the thermal barrier increased (Fig. 10). At 2 m from the thermal barrier Pl values equivalent to full sunlight values (i.e. 400 W m-2 PAR) were reached. The spectral distribution of the lamp combination tested is shown in Fig. 12. TABLE III
Reach-in cabinet: radiant energy flux density and qaantam thtx density values at standard plant container height (means of 4 readings)
T
Standard Iishting rig
.-
After 2000 h
After 100 h Light system AN
HPI
Quartz iodide
346
286
131
155
195
168
110
58
151
118
21
97
906
178
502
276
AN
Epph (400-1400 nm, W mm2) Eppley/RG8 filter (400-700 nm, W mT2) Eppley/RGS filter (700-1400 nm, W rnma) Quantum sensor (400-700 nm) (WE mb8 s-l)
-
4.3. Reach-in cabinet Using a horizontal grid (O-25 m squares), coefficients of variation were calculated to be 4,5 and 9% at 1, 1.3 and 1.8 m, respectively, from the thermal barrier. There was no marked decline in irradiance around the edge of the growing platform in these chambers. Total energy flux density, PI and PPFD values, recorded at standard plant container height are presented in Table III. PI declined by 40 W m-2 from 0.80 to 1.80 m from the thermal barrier. The spectral distribution of the lamp combination tested is shown in Fig. Il. 5. Discussion
The lighting systems described in this paper have been in operation for at least 5 years and a wide range of plant types including many horticultural, forestry and agronomic species have been grown satisfactorily under them. Plant responses to these systems, particularly where comparisons were
34
LIGHTING
SYSTEMS
made using varying combinations of high pressure discharge lamps with blue and red waveband supplementation from various lamp types, have been described in detail elsewhere.’ ’-I3 In the Climate Laboratory, various high-pressure lamps including mercury fluorescent, mercury halide, metal halide, and high-pressure sodium types have been tested and have operated satisfactorily. In this respect, new lamp types with improved plant performance characteristics can be readily incorporated, as they are released by various lamp manufacturers, into any of the systems described. In practice, the Climate Laboratory lighting system incorporating metal halide and quartz halogen lamps is more efficient than the FRI tree growth room system which was designed earlier and uses the internally reflectorized mercury-vapour fluorescent lamps with incandescent lamps. At a comparable distance from the thermal barrier, on a unit area basis, the photon flux density per watt of installed lighting is almost twice as high in the metal halide based system (even though this system also incorporates a water screen in the thermal barrier). A similar relationship between these lamp types was independently determined in the reach-in cabinet.‘l However, in spite of the less efficient energy conversion, the tree growth room system does not require reflector assemblies and allows close packing of lamps resulting in a more diffuse light source. The larger number of smaller wattage lamps also permits selective lamp switching and provides a means of generating stepped lighting programmes and a means of directly adjusting irradiance levels. Choice of the horizontally operated mercury halide lamp for the reach-in cabinet allowed the entire lamp loft assembly to be kept to a minimum height and resulted in the use of simple reflector assemblies (Figs 6 and 7). The main advantage of high-pressure discharge lamps is the ability to attain high total and photosynthetic irradiance levels equivalent to peak sunlight values. In all systems the average photosynthetic irradiances available at the standard plant container height were equivalent to half peak (midday, midsummer) sunlight values; i.e. 180 to 200 W m-2 PAR. In the large FRI tree growth rooms, this value reached 380 W m-2 (PAR) 2 m from the light source and in the Climate Laboratory CE rooms was 420 W m -2 (PAR) at normal plant container height under the high irradiance lighting system. The other main advantages of these high-pressure discharge lamp-based systems are as follows. (i) Fewer lamps are needed to obtain the irradiance required. This minimizes initial wiring and control equipment costs and also leaves considerable room in the lighting rig for the addition of further lamps if required. (ii) High-pressure discharge lamps age slower and lamp life is considerably longer than with fluorescent lamps. In practice these lamps can be used in CE units for approximately 2 years with less than a 20 % decline in PI. For example, in the FRI tree growth rooms, the PPFD output from the high-pressure mercuryvapour fluorescent lamps, after at least 12,000 h of operation, had declined by only 19 %. The point-source feature and high heat output from the lamps, are the main disadvantages of high-pressure discharge lamp-based systems. Although point sources can be a problem in CE units, reflector systems can be chosen to give very satisfactory light distributions across plant growth platforms. This problem can also be avoided by using a large number of less efficient, smaller wattage lamps or by using the internal reflector lamps similar to the high-pressure mercury-vapour fluorescent lamp used in the FRI tree growth rooms. Overlapping light from different lamps and the use of reflectorized walls also improve distribution. As with fluorescent lamp-based lighting systems, best plant uniformity is achieved where plants are moved within the CE chamber at least twice weekly to avoid any consistently high or low irradiance areas. The main disadvantage of high-pressure discharge lamps is the high heat output which must be dissipated in some way to avoid high CE chamber and plant temperatures. Plate glass thermal barriers are essential in all CE chambers whether fluorescent or high-pressure discharge lamp lit and the glass barrier appears to be all that is necessary with some high-pressure discharge lamp units (FRI tree growth rooms). The plate glass-water thermal barrier used in the DSIR CE rooms and cabinets, although introducing another component to the system, has proven to be a very satisfactory thermal barrier and is easy to operate. A desirable feature of this barrier is that the
1
J.
WARRINGTON
ET
35
AL.
temperature can be regulated to avoid condensation at the glass-air interface which can be a problem where plate-glass barriers alone are used. The most difficult physical characteristic of daylight to reproduce in artificially-lit plant growthchambers is the visible and near infra-red spectral energy distribution. Under natural lighting conditions the spectral distribution changes throughout the day depending on solar angle and sky conditions. The quality of daylight also changes, as it passes through plant canopies, to become proportionately richer in the near infra-red waveband. Very little is understood of the influence of these spectral energy distribution changes on plant growth and development.“~ l8 The daylight spectral energy distribution is continuous in the visible and near infra-red wavebands and no single artificial lighting source completely reproduces the spectral characteristics of daylight. In high-pressure discharge lamps the dominant feature of each of the spectral energy distributions (Fig. II) are the peaks which represent line emissions from each ion in the discharge tube. The high output of these lamps in the 500-600 nm waveband is a consequence of matching them to human eye response rather than to plant growth requirements. Hence incandescent lamps are used in each of the systems to enhance the red: far-red sections of the spectrum. A similar problem is encountered with fluorescent lamp based lighting systems. Downs and Hellmers8 state that the fluorescent: incandescent ratio should be adjusted so that 10% of the total illuminance, or 30% of the installed lamp wattage is provided from incandescent lamps. However, as these authors point out, the values were originally obtained in rooms using carbon arc lamps’ 9 and from older fluorescent lamp rooms. *O Although some recent re-examination of this ratio has been carried out 2’* *2there are no clear data which suggest that 10% incandescent illumination is either an adequate or an excessive amount. In the high-pressure discharge lampbased systems described in this paper up to 50% of the installed wattage is from incandescent lamps and the various plant responses tested indicate that this I :I ratio is desirable. The lighting system design is sufficiently flexible to allow addition of further incandescent lamps at a later stage if warranted by subsequent plant research. With both fluorescent lamp- and high-pressure discharge lamp-based systems the influence of varying amounts of incandescent lamps on plant growth and development responses still requires further investigation. In the past, poor spectral distribution was cited as one of the disadvantages of high-pressure discharge lamps. This was particularly the case with mercury vapour lamps. Newer phosphorcoated mercury vapour, mercury halide, metal halide and high-pressure sodium lamps have considerably improved spectral energy distributions and further improvements can be expected when special halides are incorporated in the discharge tube (e.g. tin halide23) or when phosphors are added to the lamp envelope in a similar way to the use of phosphors in fluorescent lamps (e.g. phosphor-coated metal halide lamps which have an added broad-red waveband). A major problem in this area of biology is to obtain useful data showing plant responses under each of the various lighting systems. Studies in our laboratories have shown the very dramatic differences that can occur in plant responses under apparently similar lighting systems which have contrasting complements of blue, red and far-red radiatitur.‘3 Acknowledgements
The development of the Climate Laboratory lighting systems has involved many people for a number of years. Specifically, we acknowledge Dr Kenneth J. Mitchell; the various people involved with helping in the numerous plant experiments run in the laboratory; and the various lamp manufacturers’ representatives who have helped in getting many of the lamps used in these studies. We wish also to acknowledge Dr R. J. Cameron, FRI, who was in large part responsible for the design of the FRI tree growth rooms and their lighting systems. REFERENCES
Shibles, R. Terminology pertaining to photosynthesis. Crop Sci., 1976 16 437-439 a Raper, C. D.; Smith, W. T.; Downs, R. J. Factors affecting the development of flue-cured ’
grown in artificial environments: growth responses to light schedules.
tobccco
Tob. Sci., 1975 XIX 22-25
36
LIGHTING
SYSTEMS
3 Bickford, E. D.; Dunn, S. Lighting for Plant Growth. The Kent State University Press, 1972 221 Australian Phytotron. J. agric 4 Morse, R. H.; Evans, L. T. Design and development of CERES-An Engng Res., 1962 7 128-140 ’ Nitsch, J. P. Phytotrons: Past achievements and future needs. In Crop Processes in Controlled Environments (A. R. Rees, K. E. Cockshull, D. W. Hand and R. G. Hurd, eds), pp. 33-35. London: Academic Press, 1972 6 Went, F. W. The Earhart Plant Research Laboratory. Chronica bot., 1950 12 91-108 ’ Carpenter, G. A.; Moulsley, L. J. The artificial illumination of environmental control chambers forplant growth. J. Agric. Engng Res., 1960 5 283-306 B Downs, R. J.; Hellmers, H. Environment and the Experimental ControZofPlant Growth. Experimental Botany Series, Vol. 6. London: Academic Press, 1975 146 9 Downs, R. J.; Bonaminio, V. P. Phytotron procedural manual for controlled environment research at the Southeastern Plant Environment Laboratories. North Carolina Agric. Expt. Stn Tech. Bull. No. 244, 1976 36 lo Kalbfleisch, W. Artificial light for plant growth. In Engineering Aspects of Environment Control for Plant Growth. Australia: CSIRO, 1963 266 ‘I Warrington, I. J.; Mitchell, K. J. The influence of blue- and red-biased light spectra on the growth and development ofplants. Agric. Meteorol., 1976 16 247-262 ‘O Warrington, I. J.; Mitchell, K. J. The suitability of three high intensity lamp sources for plant growth and development. J. agric. Engng Res., 1975 20 295-302 l3 Warrington, I. J.; Mitchell, K. J.; Halligan, G. Comparisons of plant growth under four different lamp combinations and various temperature and irradiance levels. Agric. Meteorol., 1976 16 231-245 I4 Warrington, I. J. (Ed.) Climate Laboratory. Palmerston North: Plant Physiology Division, Dept. of Scientific and Industrial Research, 1971 30 ‘5 Anon. Growing trees in the Laboratory. Whats New in Forest Research ? Rotorua, New Zealand: Forest Res. Inst., 1973 (4) 4 I6 Holleander, A. Radiation Biology, Vol. ZZZ. New York: McGraw-Hill, 1956 765 I7 Holmes, M. G.; Smith, H. The function of phytochrome in plants growing in the natural environment. Nature, 1975 254 512-514 ia Morgan, D. C.; Smith, H. Linear relationship between phytochrome photoequilibrium and growth in plants under simulated natural radiation. Nature, 1976 262 210-212 ‘9 Parker, M. W.; Borthwick, H. A. Growth and composition of Biloxi soybean grown in a controlled environment with radiation from difirent carbon-arc sources. Plant Physiol., 1949 24 345-358 2o Dunn, S.; Went, F. W. Influence of fluorescent light quality on growth and photosynthesis of tomato. Lloydia, 1959 22 302-324 a1 Rajan, A. K.; Betteridge, B.; Blackman, G. E. Interrelationships between the nature of the light source, ambient air temperature and the vegetative growth of difirent species within growth cabinets. Ann. Bot., 1971 35 323-342 22 Deutch, B.; Rasmussen, 0. Growth chamber illumination and photomorphogenetic efficacy. I. Physiological action of infrared radiation beyond 750 nm. Physiol. Plant., 1974 30 64-71 25 Downs, R. J., Smith, W. T.; Strickland, A, Plant response to a new type high intensity discharge lamp. Paper presented at the 1974 Summer Meeting of the ASAE, Oklahoma State University, Stillwater, Oklahoma, 23-26 June
Lighting
Systems
in Major New Zealand
Environment
Controlled
Facilities
I. J. WARRINGTON* ; T. DIXON* ; R. W.
ROBOTIIAM*
; D. A. ROOK?
The lighting systems used in New Zealand in the Department of Scientific and Industrial Research (DSIR) Climate Laboratory controlled environment rooms, the Forest Research Institute (FRI) tree growth rooms, and the DSIR-designed reach-in controlled environment chambers are described. All lighting systems are based on high-pressure discharge lamps which can be used with varying amounts of incandescent light supplementation. The main lighting type used in the Climate Laboratory controlled environment rooms is the high-pressure metal
halide lamp, that in the FRI rooms the high-pressure mercury-vapour fluorescent lamp with internal reflector, and that in the reach-in chambers a high-pressure mercury halide lamp. Details of lighting rig design, of irradiance levels obtainable, vertical and horizontal light distribution patterns and spectral quality are presented for each system. The photosynthetic irradiancelevels available at 2-3 m below the lighting systems in all of these controlled environment systems are high (180-200 W m-a PAR). In the Climate Laboratory and FRI growth rooms peak sunlight values of approximately 400 W m-a PAR (approximately 10,000 ft.c.) have been achieved. A discussion of the performance of these systems is also presented.
1. Introduction A major area of interest in controlled environment biology is the supply of light to plant growth chambers where daylight is completely excluded. Lamp systems used in these situations should simulate daylight as closely as possible. Consequently design features should take account of plant requirements for photosynthesis, for photomorphogenesis and for photoperiodism. Hence the system should (1) provide an adequate photosynthetic photon flux density (PPFD)’ in the photosynthetically active range (PAR), 400-700 nm, (2) have a satisfactory spectral energy distribution in the photosynthetically active and near infra-red wavebands. and (3) provide control over the duration of lighting. In addition, it may be useful to have the capacity, in an artificial lighting system, to change the irradiance at different times of the day (i.e. provide stepped lighting programmes compared with the usual square-wave programme?) and to change the spectral energy distribution during the course of the day in a similar manner to natural daylight changes. In practice few of these requirements are completely satisfied m controlled environment lighting systems and insufficient experimentation has been undertaken to characterize the nature and magnitude of the design inadequacies that may exist. The majority of both reach-in and walk-in controlled environment (CE) chambers constructed and operated through the 1950 to 1970 period used fluorescent-lamp based systems supplemented with various proportions of incandescent lighting 3- ‘O. Details of vertical and horizontal light distribution patterns within these CE chambers, maximum irradiance levels achieved and information on lamp ageing characteristics have been presented by Carpenter and Moulsley’, Downs and coworkers** 9 and Kalbfleisch’O for a range of facilities in different countries. In general, fluorescent-lamp based systems produce photosynthetic photon flux densities (PPFD) of approximately 650 to 750 microeinsteins m --2 s-r (i.e. equivalent to less than half of full sunlight values), result in a very even distribution of light energy across the plant growing platform with some decline around the edges, but have undesirable ageing characteristics (i.e. approximately 20 to 25 ‘A decline in light output after 4000 h or 1 year of operation).’ The main *Climate Laboratory, Plant Physiology Division, D.S.I.R., Palmerston North, New Zealand tForest Research Institute, New Zealand Forest Service, Rotorua, New Zealand Received 16 May 1977; accepted in revised form 4 July 1977 23
24
LIGHTING
SYSTEMS
technical advantage of these systems is that they have a low heat output, and although adequate ventilation must be assured for the maintenance of proper lamp operating temperatures,B generally only a simple barrier of transparent plastic or plate glass is required between the lamps and the plant growth chamber. In recent years, high-pressure discharge lamps have been extensively used in CE units of various sizes from reach-in chambers to walk-in rooms. Although plants perform and grow well under these lamps” -13 there are no published data on the physical design or performance of highpressure discharge lamp-based lighting systems. In this paper we describe the systems used in the New Zealand Department of Scientific and Industrial Research (DSIR) Climate Laboratory rooms, the NZ Forest Service Forest Research Institute (FRI) tree growth rooms and the DSIRdesigned reach-in CE chambers. Air out
I@\-
,
-
r--x== ----
El.00
Airout2
-
r
Fig. I. Cross-sectiondiagrams of ClimateLoboratory CE room (left) and FRI tree growth room (right). ANdimensions are in metres. A, lamp loft; B, movable lighting rig; C, lamp ballast and control equipment; D, thermal barrier; E, plant growth chamber; F, side and rear wallmirrors; G, reflective whiteinterior walls; H, plant growth trolleys at standard height: I, slottedjloor; J, reflective aluminium-foil wall-liner: K, movable floor; L, plant root containers
2. Controlled environment facilities 2.1.
General
The general features of the Climate Laboratory CE rooms’ 4 and those of the FRI tree growth rooms15 have been described elsewhere. A cross-section diagram of each design is shown in Fig. I. The DSIR-designed reach-in cabinet (made under license by Temperzone Ltd, Auckland, N.Z.) is a small version of the Climate Laboratory CE room; the plant growth chamber measures 1.2 x 0.9 x I.8 m high.
I. J.
WARRINGTON
El-
AL.
25
All of the lighting rig/lamp loft configurations described for these systems have been designed to permit the joint use of high pressure discharge lamps, which provide the high photosynthetic photon flux densities desirable for plant growth, and quartz halogen or incandescent lamps, which provide photoperiodic lighting as well as the supplementary red and far-red light necessary for photomorphogenesis and photosynthesis. Hence the combined use of 2 lamp types results in a balanced visible and far-red spectrum necessary for normal plant growth and development. High plant growth-chamber temperatures have been minimized by the combined use of thermal barriers and high rates of lamp loft ventilation. Unlike many of the fluorescent lamp based systems in use, the systems described allow easy lamp access even during plant growth-chamber operation. The size and accessibility of the lamp lofts and lighting rigs also allow the addition or replacement of new lamp types as advances in lighting technology produce improved lamps.
Fig. 2. Climate Laboratory CE room. A stanaiwdlighting rig in the operuting position above a CE room. Fluted reflectors house the high-pressure discharge lamps. Lamp control gear is readily accessible on the top of the rig. The portable lighting rig frame is easily removed from above the room for repairs and maintenance
2.2. DSlR Climate Laboratory Lamps are mounted on a movable frame in the lamp loft above each plant growth chamber (Figs 2 and 3). The frame measures 2.70 x 1.80x I.10 m high and straddles the 3.00 x 1.60 m plate glass-water thermal barrier. The loft measures 3.20 x 2.40 x 1.90 m high and is air cooled to maintain a temperature of approximately 30°C. Electricity is supplied to the rig by 4 flexible, trailing cables (&phase, 70 A capacity per phase) which connect to junctions for the high-pressure discharge lamp ballast and control gear, or for direct supply to the quartz halogen and incandescent lamps. The high-pressure discharge lamp ballast and control gear are mounted directly on the lamp rig and are air cooled with the lamps. All ballast and lamp types tested in the Laboratory to date have been mounted on the rig in this way. Individual wiring systems are employed to allow separate timing of the main photosynthetic lighting system and of the smaller incandescent photoperiod lamps. The electrical supply is voltage controlled to f2% and constant-voltage ballasts are used to ensure stable light output from the high-pressure discharge lamps. In the event of a power failure, a standby diesel-fueled power supply allows the operation of the photoperiod lights in all CE rooms and of the main photosynthetic lights in selected CE rooms. Horizontal and vertical placement of the lamp and reflector assemblies is achieved simply by mounting the lamp holders on horizontal beams at
26
LIGHTING
SYSTEMS
different heights across the lighting rig. The faces of all reflectors are adjusted to be 10 cm from the plate glass-water thermal barrier. The lamp and reflector-assembly angle can be adjusted from a simple swivel-mount at each reflector base. Each lamp rig can be withdrawn from the lamp loft for checking light operation, for maintenance, or for reconstruction using different lamp types. The standard lighting combination comprises 4 x 1000 W “Metalarc” high-pressure metal halide lamps (Ml000 BU Sylvania) and 4 x 1000 W quartz halogen lamps (Philips type 12012 R). A high irradiance system was also tested; this comprised 6 x 1500 W “Metalarc” high-pressure metal halide lamps (M 1500 BU Sylvania) and 8 x 1000 W quartz halogen lamps. The reflectors used for the high-pressure discharge lamps were the Duraglow (General Electric Co.) type, and for the quartz halogen type the Philips reflector housing NK 17/00. On all lamp rigs, 6 x 150 W incandescent lamps (Mazda reflected flood) are used to provide low irradiance photoperiodic lighting.
Fig. 3. Climate Laboratory CE room. View of part of a standard lighting rig in operating position above the plateglass-water thermal barrier. Mirrored wallpanels produce multiple images. Air inlet grills along each side of the room are also shown
The plant growth chamber is separated from the lamp loft by a thermal barrier comprising a single sheet of 8 mm plate glass supporting a 3.5 cm deep water layer. The water flow rate is 16-18 1 min-l. Water temperature is controlled to be similar to the plant growth chamber temperature in order to avoid condensation at the glass-air interface. The thermal-barrier water is within a closed system; in which either warm water is supplied to the barrier from a small adjacent tank (1 kW heating element) that forms part of a secondary circulation system, or cold water is supplied from the central holding tank directly to the thermal barrier. Water leaving the barrier returns to the central holding tank where cooling, filtration and algicide injection occurs. Each barrier is cleaned twice a week with a vacuum line to remove dead algae and accumulated dirt particles. To improve light distribution within the plant growth chamber, mirrors are surface mounted to the walls and air ducting systems and extend from plant growing height to the underside of the plate glass-water thermal barrier.
I. J.
WARRINGTON
ET
27
AL.
Fig. 4. FRI tree growth rooms. View of lighting rig with one of its air inlets as seen from within the controlled environment room through the glass screen. The aluminium foil liner has been fitted and the air inlet grille and part of the support structure for the movable steel floor are also shown
2.3.
FRI tree growth room.,
Each 3.3 x 3.3 m welded steel lamp rig can accommodate 162 x 400 W high-pressure mercuryvapour lamps with internal reflectors (Philips HPLR-N) and 162 x 150 W low heat output incandescent lamps (Philips Attralux PAR38). The incandescent and mercury-vapour lamps are evenly distributed throughout the lighting rig (Figs 4 and 5) and each lamp type is arranged on a separate timing system. In the tests reported here however, only 119 incandescent lamps were used with 162 mercury vapour lamps. The incandescent lamps provide photoperiodic lighting as
Fig. 5. FRI tree growth rooms. View of lighting rig on its overhead rail svstem. The ventilated cabinets housing the lamp control equipment and ballasts are on the right of the figure
28
LIGHTING
SYSTEMS
well as the supplementary red and far-red light necessary for photomorphogenesis and photosynthesis. All lamps are cooled by filtered air (340 m3 min-l) which enters from opposite sides of the loft and is vented via a jet fan positioned above the centre of the lamp rig. A screen of heat-toughened plate glass, 6.4 mm thick, and sub-divided into 12 sections, each 0.9 x 1.2 m, is supported on a steel frame which separates the growing space from the lighting system. No water thermal barrier is used.
Fig, 6. Reach-in cabinet. A lighting rig in the servicing position on the overhead rails outside of the cabinet. Mirrored wall panels and air outlet grills are shown within the plant growth chamber
Each lamp rig can be withdrawn from the 3.7 x 3.7 x 1.4 m high lamp loft on an overhead rail system for checking light operation, for maintenance, or for reconstruction using different lighting units. Power is supplied to each rig by ten trailing cables. The lamps can be manually switched off in pairs thus allowing a range of irradiance levels and distributions of light to be provided. In the event of a power failure, a standby diesel-fueled power supply allows 24 incandescent lamps in each rig to be operated. The ballasts for the high-pressure discharge lamps are mounted separately from the main lighting rig, on thick aluminium plates in cabinets which are fitted with individual air circulation/ ventilation systems for heat dissipation. To improve light distribution across the tree growth chamber each wall is lined with heavyduty aluminium foil to increase reflectance. Outlets have been provided for the installation of up to 8 kW of lighting laterally within the chamber.
I.
J. WARRINGTON
ET
29
AL.
2.4.
Reach-in cabinet
The lamp fittings are mounted directly on a sheet of heat-resistant material (“Formica”) which is suspended from an overhead dual railing system. The 2.73 x 1.02 x0.70 m high lamp loft is air-cooled with a 40-cm fan which draws filtered air through the system. The lighting combination used in the tests comprised 6 x 375 W high-pressure mercury halide lamps (Philips HPI/T in Philips HGH 375 reflector fittings) and 2 x 1000 W quartz halogen lamps (Philips type 12012R in Philips QGH 1000 reflector fittings). In addition, 3 x 100 W incandescent (Philips inside-frosted) lamps were installed for photoperiod lighting @g,s 6 and 7). Ballast and control equipment for the lamps are mounted in a separate, ventilated cabinet on the outside of the plant growth chamber. The plate glass-water thermal barrier is similar in performance and design to that in the Climate Laboratory CI rooms. All internal walls of the plant growth chamber are lined with 8 mm plate-glass mirror,.
Fig. 7. Reach-in cabinet, Plan view of cabinet lighting rig. Both the high pressure discharge (old1 ,side rows) and quartz hak rgen lamps (central Ipow) are housed in similar reflectors. Three low-irrtensity photope?riod extension lamps are spaced along the centre of the rig
3. Measurement instrumentation and technique Light uniformity was measured at set distances from the thermal barriers over a horizontal grid system using an EEL photometer without a fitted cosine-corrected head (Evans Electroselenium Ltd, Essex, England). Measured values were used to determ:ne coefficients of variation of the light distribution. The spectral distribution of each lighting system was measured with an ISCO spectroradiometer and record-scanner (Instrumentation Specialities Co., Lincoln, Nebraska, U.S.A.). Total and photosynthetic energy flux densities were recorded using an Eppley pyranometer (Eppley Lab., Newport, U.S.A.) plus a Schott RG8 (Schott and Gen., Mainz, W. Germany) filter system. Values are presented for 380-700 (photosynthetically active radiation, PAR), 700-1400 and 380-1400 nm wavebands where a plate glass-water thermal barrier was used16, or as 380-700, 700-2500 and 380-2500 nm wavebands where a plateglass thermal barrier was used.
30
LIGHTING
h&IkP
87
-0-45
SYSTEMS
87
mI.80
m
Fig. 8. Relative light meter values recorded with an EEL photometer, on a I.8 x 1.8 m horizontal grid 2 m from the thermal barrier in a Climate Laboratory CE room (standard lighting rig). Underlined values represent PPFD and energy flux density measurement locations
Photosynthetic photon flux density (PPFD) was measured with a Lambda quantum sensor (Lambda Instruments Corp., Lincoln, Nebraska, U.S.A., meter LI 185, sensor S/N Q152/725). The spectral distribution, and energy and PPFD values presented are means of measurements recorded at several places on the horizontal grid systems. 4. Performance of lamp systems 4.1. Climate Laboratory CE rooms A typical light distribution pattern for values recorded on a 1a8x l-8 m square grid (O-45 m squares) across a horizontal plane at normal plant container height, 2 m from the thermal barrier, is shown in Fig. 8. At 1.5 m from the thermal barrier the coefficient of variation was 12 ‘X and at 2.5 m, 3%. it short distances from the thermal barrier, irradiance levels declined towards the side walls (Fig. 9). I
0.0
0.5
“_
I.0 Oktome
ocmss
grid
(m
1
Fig. 9. Light distribution at various distances from the thermal barrier in a Climate Laboratory CE room. Top, 1.18 m; middle, 2.00 m; bottom, 2.9 m. M, Centre front to centre rear: O---O, centre side to centre side (standard lighting rig)
I. J.
WARRINGTON
ET
31
AL. TABLE I
Climate L&oratory CE room: radiant energy ffux density and quantum flux density values at standard plant container height (means of 5 readings) Standard
___-
Light system
Eppley (400-1400 nm, W m-*) Eppley/RGI filter (400-700 nm, W m- *) Eppley/RGI filter (700-1400 rim, W mv2) Quantum sensor (400-700 Ml) (pE md2 s-l)
High irradiance rig*
lighting rig* Quart.: iodide ___-
All
Metal-arc
All
206
150
51
485
154
137
20
365
52
13
31
120
632
552
94
1665
*After 2000 h operation
I
55-%-T+-
0.4
0.8
I.2
I.6
Distance from thermal
Fig. 10. PAR
horizontal
8.0
2-O
2.4
barrier
2.8
(m )
fluxes at various distances from the thermal barrrer. Top, FRZ tree growth Climate Laboratory CE room. a, Quantum flux; o, PAR energy flux
room; bottom,
32
LIGHTING TABLE
SYSTEMS
II
FRI tree growth room: radiant energy flux density and qaantmn flax density values at several measurement heights (means of 6 readings)* Light system Distance from thermal barrier, m
~__ Eppley (400-2500 nm, W mm2) Eppley/RGI filter (400-700 nm, W me2) Epply/RGS filter (700-2500 nm, W m- *) Quantum sensor (400-700 Ml) (pE m-2 s-l )
2
4
6
8
841
624
488
372
386
386
289
223
167
455
335
265
1620
1227
903
4
6
296
240
192
248
189
52
41
205
138
107
188
151
702
997
763
231
189
-
416
-
*After 2OW h operation
Z-
‘E c
“: E
I.6 1*4-
2
;:;_
.‘; ;
0*8-
+ 2
0.6 0.4 0.2 -
/v I
Lx. $ 15 I.8 I.6 I.4 I.2
I
I
I
-
d:; 0.6 0.4 o-2 :L& 400
500
600
Wavelength
(nm)
700
Fig. II. Spectral energy distribution for each lighting system. Top, Climate Laboratory CE room: centre, FRI tree growth room; bottom, reach-in cabinet
I. J. WARRINGTON
33
ET AL.
Total energy flux, photosynthetic irradiance (PI) and PPFD values for both the standard and high irradiance lamp combinations are shown in Table I. Photosynthetic irradiance (PI) declined curvilinearly over the normal plant growing height interval (i.e. 1.2 to 2.6 m below the thermal barrier); the rate was approximately 70 W m-2 m-l (Fig. 10). The spectral distribution of the lamp combination tested is shown in Fig. 11. 4.2. FRI tree growth rooms Light distribution patterns were recorded on a horizontal grid (060 m squares) at several distances from the thermal barrier. The coefficients of variation were 7, 10, 8 and 7 % at 2, 4, 6 and 8 m, respectively, from the barrier. As in the Climate Laboratory CE rooms, these values confirm the even nature of light distribution across the plant growing area; a decline in irradiance was recorded around the outer limit of the measurement grid but these values were not included in the coefficient of variation calculations as the measurements were outside of the normal plant growing area. Total energy flux, PI and PPFD values are presented in Table II for several measurement heights. PI declined curvilinearly (approximately 35 W m -2 m - ‘) as the distance from the thermal barrier increased (Fig. 10). At 2 m from the thermal barrier Pl values equivalent to full sunlight values (i.e. 400 W m-2 PAR) were reached. The spectral distribution of the lamp combination tested is shown in Fig. 12. TABLE III
Reach-in cabinet: radiant energy flux density and qaantam thtx density values at standard plant container height (means of 4 readings)
T
Standard Iishting rig
.-
After 2000 h
After 100 h Light system AN
HPI
Quartz iodide
346
286
131
155
195
168
110
58
151
118
21
97
906
178
502
276
AN
Epph (400-1400 nm, W mm2) Eppley/RG8 filter (400-700 nm, W mT2) Eppley/RGS filter (700-1400 nm, W rnma) Quantum sensor (400-700 nm) (WE mb8 s-l)
-
4.3. Reach-in cabinet Using a horizontal grid (O-25 m squares), coefficients of variation were calculated to be 4,5 and 9% at 1, 1.3 and 1.8 m, respectively, from the thermal barrier. There was no marked decline in irradiance around the edge of the growing platform in these chambers. Total energy flux density, PI and PPFD values, recorded at standard plant container height are presented in Table III. PI declined by 40 W m-2 from 0.80 to 1.80 m from the thermal barrier. The spectral distribution of the lamp combination tested is shown in Fig. Il. 5. Discussion
The lighting systems described in this paper have been in operation for at least 5 years and a wide range of plant types including many horticultural, forestry and agronomic species have been grown satisfactorily under them. Plant responses to these systems, particularly where comparisons were
34
LIGHTING
SYSTEMS
made using varying combinations of high pressure discharge lamps with blue and red waveband supplementation from various lamp types, have been described in detail elsewhere.’ ’-I3 In the Climate Laboratory, various high-pressure lamps including mercury fluorescent, mercury halide, metal halide, and high-pressure sodium types have been tested and have operated satisfactorily. In this respect, new lamp types with improved plant performance characteristics can be readily incorporated, as they are released by various lamp manufacturers, into any of the systems described. In practice, the Climate Laboratory lighting system incorporating metal halide and quartz halogen lamps is more efficient than the FRI tree growth room system which was designed earlier and uses the internally reflectorized mercury-vapour fluorescent lamps with incandescent lamps. At a comparable distance from the thermal barrier, on a unit area basis, the photon flux density per watt of installed lighting is almost twice as high in the metal halide based system (even though this system also incorporates a water screen in the thermal barrier). A similar relationship between these lamp types was independently determined in the reach-in cabinet.‘l However, in spite of the less efficient energy conversion, the tree growth room system does not require reflector assemblies and allows close packing of lamps resulting in a more diffuse light source. The larger number of smaller wattage lamps also permits selective lamp switching and provides a means of generating stepped lighting programmes and a means of directly adjusting irradiance levels. Choice of the horizontally operated mercury halide lamp for the reach-in cabinet allowed the entire lamp loft assembly to be kept to a minimum height and resulted in the use of simple reflector assemblies (Figs 6 and 7). The main advantage of high-pressure discharge lamps is the ability to attain high total and photosynthetic irradiance levels equivalent to peak sunlight values. In all systems the average photosynthetic irradiances available at the standard plant container height were equivalent to half peak (midday, midsummer) sunlight values; i.e. 180 to 200 W m-2 PAR. In the large FRI tree growth rooms, this value reached 380 W m-2 (PAR) 2 m from the light source and in the Climate Laboratory CE rooms was 420 W m -2 (PAR) at normal plant container height under the high irradiance lighting system. The other main advantages of these high-pressure discharge lamp-based systems are as follows. (i) Fewer lamps are needed to obtain the irradiance required. This minimizes initial wiring and control equipment costs and also leaves considerable room in the lighting rig for the addition of further lamps if required. (ii) High-pressure discharge lamps age slower and lamp life is considerably longer than with fluorescent lamps. In practice these lamps can be used in CE units for approximately 2 years with less than a 20 % decline in PI. For example, in the FRI tree growth rooms, the PPFD output from the high-pressure mercuryvapour fluorescent lamps, after at least 12,000 h of operation, had declined by only 19 %. The point-source feature and high heat output from the lamps, are the main disadvantages of high-pressure discharge lamp-based systems. Although point sources can be a problem in CE units, reflector systems can be chosen to give very satisfactory light distributions across plant growth platforms. This problem can also be avoided by using a large number of less efficient, smaller wattage lamps or by using the internal reflector lamps similar to the high-pressure mercury-vapour fluorescent lamp used in the FRI tree growth rooms. Overlapping light from different lamps and the use of reflectorized walls also improve distribution. As with fluorescent lamp-based lighting systems, best plant uniformity is achieved where plants are moved within the CE chamber at least twice weekly to avoid any consistently high or low irradiance areas. The main disadvantage of high-pressure discharge lamps is the high heat output which must be dissipated in some way to avoid high CE chamber and plant temperatures. Plate glass thermal barriers are essential in all CE chambers whether fluorescent or high-pressure discharge lamp lit and the glass barrier appears to be all that is necessary with some high-pressure discharge lamp units (FRI tree growth rooms). The plate glass-water thermal barrier used in the DSIR CE rooms and cabinets, although introducing another component to the system, has proven to be a very satisfactory thermal barrier and is easy to operate. A desirable feature of this barrier is that the
1
J.
WARRINGTON
ET
35
AL.
temperature can be regulated to avoid condensation at the glass-air interface which can be a problem where plate-glass barriers alone are used. The most difficult physical characteristic of daylight to reproduce in artificially-lit plant growthchambers is the visible and near infra-red spectral energy distribution. Under natural lighting conditions the spectral distribution changes throughout the day depending on solar angle and sky conditions. The quality of daylight also changes, as it passes through plant canopies, to become proportionately richer in the near infra-red waveband. Very little is understood of the influence of these spectral energy distribution changes on plant growth and development.“~ l8 The daylight spectral energy distribution is continuous in the visible and near infra-red wavebands and no single artificial lighting source completely reproduces the spectral characteristics of daylight. In high-pressure discharge lamps the dominant feature of each of the spectral energy distributions (Fig. II) are the peaks which represent line emissions from each ion in the discharge tube. The high output of these lamps in the 500-600 nm waveband is a consequence of matching them to human eye response rather than to plant growth requirements. Hence incandescent lamps are used in each of the systems to enhance the red: far-red sections of the spectrum. A similar problem is encountered with fluorescent lamp based lighting systems. Downs and Hellmers8 state that the fluorescent: incandescent ratio should be adjusted so that 10% of the total illuminance, or 30% of the installed lamp wattage is provided from incandescent lamps. However, as these authors point out, the values were originally obtained in rooms using carbon arc lamps’ 9 and from older fluorescent lamp rooms. *O Although some recent re-examination of this ratio has been carried out 2’* *2there are no clear data which suggest that 10% incandescent illumination is either an adequate or an excessive amount. In the high-pressure discharge lampbased systems described in this paper up to 50% of the installed wattage is from incandescent lamps and the various plant responses tested indicate that this I :I ratio is desirable. The lighting system design is sufficiently flexible to allow addition of further incandescent lamps at a later stage if warranted by subsequent plant research. With both fluorescent lamp- and high-pressure discharge lamp-based systems the influence of varying amounts of incandescent lamps on plant growth and development responses still requires further investigation. In the past, poor spectral distribution was cited as one of the disadvantages of high-pressure discharge lamps. This was particularly the case with mercury vapour lamps. Newer phosphorcoated mercury vapour, mercury halide, metal halide and high-pressure sodium lamps have considerably improved spectral energy distributions and further improvements can be expected when special halides are incorporated in the discharge tube (e.g. tin halide23) or when phosphors are added to the lamp envelope in a similar way to the use of phosphors in fluorescent lamps (e.g. phosphor-coated metal halide lamps which have an added broad-red waveband). A major problem in this area of biology is to obtain useful data showing plant responses under each of the various lighting systems. Studies in our laboratories have shown the very dramatic differences that can occur in plant responses under apparently similar lighting systems which have contrasting complements of blue, red and far-red radiatitur.‘3 Acknowledgements
The development of the Climate Laboratory lighting systems has involved many people for a number of years. Specifically, we acknowledge Dr Kenneth J. Mitchell; the various people involved with helping in the numerous plant experiments run in the laboratory; and the various lamp manufacturers’ representatives who have helped in getting many of the lamps used in these studies. We wish also to acknowledge Dr R. J. Cameron, FRI, who was in large part responsible for the design of the FRI tree growth rooms and their lighting systems. REFERENCES
Shibles, R. Terminology pertaining to photosynthesis. Crop Sci., 1976 16 437-439 a Raper, C. D.; Smith, W. T.; Downs, R. J. Factors affecting the development of flue-cured ’
grown in artificial environments: growth responses to light schedules.
tobccco
Tob. Sci., 1975 XIX 22-25
36
LIGHTING
SYSTEMS
3 Bickford, E. D.; Dunn, S. Lighting for Plant Growth. The Kent State University Press, 1972 221 Australian Phytotron. J. agric 4 Morse, R. H.; Evans, L. T. Design and development of CERES-An Engng Res., 1962 7 128-140 ’ Nitsch, J. P. Phytotrons: Past achievements and future needs. In Crop Processes in Controlled Environments (A. R. Rees, K. E. Cockshull, D. W. Hand and R. G. Hurd, eds), pp. 33-35. London: Academic Press, 1972 6 Went, F. W. The Earhart Plant Research Laboratory. Chronica bot., 1950 12 91-108 ’ Carpenter, G. A.; Moulsley, L. J. The artificial illumination of environmental control chambers forplant growth. J. Agric. Engng Res., 1960 5 283-306 B Downs, R. J.; Hellmers, H. Environment and the Experimental ControZofPlant Growth. Experimental Botany Series, Vol. 6. London: Academic Press, 1975 146 9 Downs, R. J.; Bonaminio, V. P. Phytotron procedural manual for controlled environment research at the Southeastern Plant Environment Laboratories. North Carolina Agric. Expt. Stn Tech. Bull. No. 244, 1976 36 lo Kalbfleisch, W. Artificial light for plant growth. In Engineering Aspects of Environment Control for Plant Growth. Australia: CSIRO, 1963 266 ‘I Warrington, I. J.; Mitchell, K. J. The influence of blue- and red-biased light spectra on the growth and development ofplants. Agric. Meteorol., 1976 16 247-262 ‘O Warrington, I. J.; Mitchell, K. J. The suitability of three high intensity lamp sources for plant growth and development. J. agric. Engng Res., 1975 20 295-302 l3 Warrington, I. J.; Mitchell, K. J.; Halligan, G. Comparisons of plant growth under four different lamp combinations and various temperature and irradiance levels. Agric. Meteorol., 1976 16 231-245 I4 Warrington, I. J. (Ed.) Climate Laboratory. Palmerston North: Plant Physiology Division, Dept. of Scientific and Industrial Research, 1971 30 ‘5 Anon. Growing trees in the Laboratory. Whats New in Forest Research ? Rotorua, New Zealand: Forest Res. Inst., 1973 (4) 4 I6 Holleander, A. Radiation Biology, Vol. ZZZ. New York: McGraw-Hill, 1956 765 I7 Holmes, M. G.; Smith, H. The function of phytochrome in plants growing in the natural environment. Nature, 1975 254 512-514 ia Morgan, D. C.; Smith, H. Linear relationship between phytochrome photoequilibrium and growth in plants under simulated natural radiation. Nature, 1976 262 210-212 ‘9 Parker, M. W.; Borthwick, H. A. Growth and composition of Biloxi soybean grown in a controlled environment with radiation from difirent carbon-arc sources. Plant Physiol., 1949 24 345-358 2o Dunn, S.; Went, F. W. Influence of fluorescent light quality on growth and photosynthesis of tomato. Lloydia, 1959 22 302-324 a1 Rajan, A. K.; Betteridge, B.; Blackman, G. E. Interrelationships between the nature of the light source, ambient air temperature and the vegetative growth of difirent species within growth cabinets. Ann. Bot., 1971 35 323-342 22 Deutch, B.; Rasmussen, 0. Growth chamber illumination and photomorphogenetic efficacy. I. Physiological action of infrared radiation beyond 750 nm. Physiol. Plant., 1974 30 64-71 25 Downs, R. J., Smith, W. T.; Strickland, A, Plant response to a new type high intensity discharge lamp. Paper presented at the 1974 Summer Meeting of the ASAE, Oklahoma State University, Stillwater, Oklahoma, 23-26 June