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New obstruction lighting system for aviation safety
Engineering Structures 132 (2017) 531–539
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Engineering Structures journal homepage: www.elsevier.com/locate/engstruct
New obstruction lighting system for aviation safety F. Pérez-Ocón a,⇑, A.M. Pozo a, O. Rabaza b a b
Department of Optics, University of Granada, Granada 18071, Spain Department of Civil Engineering, University of Granada, Granada 18071, Spain
a r t i c l e
i n f o
Article history: Received 5 October 2015 Revised 18 November 2016 Accepted 21 November 2016
Keywords: Beacon Repair Maintenance ease Work safety Availability LEDs Integrating spheres Optical fibers
a b s t r a c t Signposting and illuminating obstacles is meant to reduce risks to aircraft by aiding the pilot in locating dangers. However, many of the obstacles to air transport, such as telecommunication towers, can surpass heights of 45 m. This implies that the installation or repair of the beacon system can involve serious risks to the personnel in charge of such work, as the tower must be climbed with the use of harnesses, helmets, and other means of protection with the hazards that these involve. To avoid these drawbacks, in this study we have designed an obstruction lighting system in which the light source lies at the base of the structure and the light, travelling through a bundle of optical fibers, rises to any point of the telecommunication tower, pole, chimney, stack or similar skeletal structures. Therefore, the proposed system would provide a major improvement in safety, not only for air traffic, but also for workers. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The rapid development of LEDs (light-emitting diodes) as new sources of light emission have made them the current light indicators in electronic devices and systems, light-signalling systems, and exterior and interior illumination systems. As the characteristics of LEDs have improved with the introduction of new manufacturing and design technology, in-depth studies have been made regarding the application of these as signalling and illumination systems in general [1–6]. These studies have been made by companies which specialize in the manufacture of illumination systems based on LED technology, such as traffic lights and street lights. Illumination systems with LEDs constitute an effective and lowcost alternative for signalling fixed obstacles (chimneys, telecommunication towers, high buildings, etc.) and even mobile ones, although the position of these signalling devices, as with conventional beacons, poses problems. The signalling and illumination of obstacles is intended to lower the risks for aircraft, as it helps the pilot to locate potential dangers. This does not necessarily diminish the limitations of operation imposed by an obstacle, but when it is not possible to ⇑ Corresponding author at: Department of Optics, Science Faculty, Edificio Mecenas, Campus Universitario de Fuentenueva, University of Granada, 18071 Granada, Spain. E-mail address: [email protected] (F. Pérez-Ocón). http://dx.doi.org/10.1016/j.engstruct.2016.11.054 0141-0296/Ó 2016 Elsevier Ltd. All rights reserved.
eliminate the obstacle and it does not affect the safety or regularity of air service, the obstacle should be properly signposted and illuminated to be seen clearly by pilots under any weather and visibility conditions. Markers displayed on or adjacent to objects shall be located in conspicuous positions so as to retain the general definition of the object and shall be recognizable in clear weather from a distance of at least 1000 m for an object to be viewed from the air and 300 m for an object to be viewed from the ground in all directions in which an aircraft is likely to approach the object [7]. It should be taken into account that many of the obstacles for air transport, such as telecommunication towers, high-voltage towers, or wind turbines can reach heights of more than 45 m. This implies that the installation or repair of any beacon system can involve serious risks to the workers in charge of these tasks, as the tower must be climbed with harnesses, helmets and other protective devices that in themselves represent hazards and discomfort for the worker. In addition, the tools used (usually heavy) can fall from considerable heights and injure operators at the foot of the tower. Furthermore, the beacons of the telecommunication towers can weigh between 5 and 20 kg, so that a 300 m-high tower with 14 beacons could bear weights of more than 280 kg in light signalling alone. To avoid the above drawbacks, in this study we have designed an obstruction lighting system for fixed obstacles. The new system consists of placing a LED matrix at the bottom of the obstacle; by
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means of integrating spheres and optical fibers, the light is conducted from the bottom to the top of the structure that needs to be illuminated. In this way, when it is necessary to make a repair, operators do not have to climb the structure, since the repair is made on the ground. Finally, we have calculated the parameters of the new obstruction lighting system that meets the International Civil Aviation Organization (ICAO) lighting requirements [7,8]. 2. Materials: LEDs, integrating spheres, and optical fibers In this study, we have used materials that comply with the rules of the FAA (Federal Aviation Administration) of the U.S. Department of Transportation [9], which are more restrictive than international regulations in terms of working at certain temperatures and humidity, etc. 2.1. Red LED For the design of the system, we propose an encapsulated LED that permits the formation of matrices in a practical, convenient way. The LED, chosen for its characteristics, was SST-90-R LEDs from Luminus Devices, Inc. This LED is used in many applications, for instance, as beacons and obstruction lighting. The LED emission area is 9 mm2, the luminous flux is 1500 lm at 9 A, the radiant efficacy at this wavelength is 269.0 lm/W, and the dominant wavelength 618 nm. It has a DC forward voltage of 2.5 V (system operating on DC volts 24–48 V [9]), a DC forward intensity current of 350 mA (current 75–500 mA [9]), an operating temperature of between 40 °C and 120 °C (40° to 55 °C [9]), and a limit maintained temperature of 217 °C. 2.2. Integrating sphere To collect all the luminous flux which exits the LED into the optical fiber, we have incorporated an integrating sphere into our design. The 200 (50.8 mm diameter) sphere used are from Edmund Optics Ltd. The reason for using this device is to collect the spatial radiant flux in order to spatially integrate the flux to maximize its injection into the optical fiber. The sphere is coupled with the LED in a port, and in a second port in front of it, we couple the optical fiber with a SMA connector to inject as much light as possible within the optical fiber. The inner reflectance of the integrating sphere is 0.95. 2.3. Optical fiber The optical fiber proposed is the FV100010501250 from Polymicro TechnologiesTM. The core diameter, cladding, and buffer are 1 mm, 1.05 mm, and 1.25 mm, respectively. It is an optical fiber with a profile-step index, high AOH silica core, doped silica clad, and high-temperature acrylate buffer. The optical fiber can operate between 65 °C and 300 °C (intermittently up to 400 °C). It has a numerical aperture of 0.22 and its full acceptance cone is 25.4°. The attenuation is 30, 15, and 10 dB/km around 457, 586 and 630 nm, respectively. A silica optical fiber was chosen because the degradation is less than for plastic optical fiber (POF) [10]. The LED emits a light beam which enters the integrating sphere and then the light enters the endface of the optical fiber (changing the refractive index); at the exit, again, there is a change in the refractive index, from optical fiber to air. Therefore, it is essential to take into account the Fresnel reflection loss twice. The calculated Fresnel reflection loss is 0.74 dB.
3. Results and discussion The general scheme is shown in Fig. 1. More specifically, we have developed our design for a telecommunication tower, although it could be applied to any fixed structure mentioned in Annex 14 of the Convention on International Civil Aviation [7,8]. As mentioned in Section 2.3, the LED emits a light beam which enters the integrating sphere and then the light enters the endface of the optical fiber. Therefore, it is essential to take into account the Fresnel reflection loss due to the change in the refractive index. The calculated Fresnel reflection loss is 0.74 dB. We have simulated all the radiation process with Zemax-EE V. 2005. Dimensions of the LED are shown in Fig. 2. We then modelled the integrating sphere with Zemax in the same way. Fig. 3 shows the shaded model of the 200 integrating spheres. Fig. 4 shows the power injected into the optical fiber at the exit of the integrating sphere. The peak of irradiance is 5.22 W/cm2 and the total power 5.05 W. Fig. 5 shows the general schematic of the device, as well as the situation of the elements for a telecommunication tower. Following the amendment 11 to Annex 14 [8], for poles, radio, and television towers and similar skeletal structures, the light must be type B fixed of low-intensity and type C fixed of medium-intensity. We present the results for the different heights in Fig. 6. 3.1. Tower up to 45 m The power at the endface of one optical fiber is:
Po ¼ P i eaL AF ¼ 3:21 W
ð1Þ
where Pi is the entrance power in the optical fiber, a is the attenuation coefficient, L the length of the optical fiber for tower up to 45 m, and AF is the Fresnel reflection attenuation. The luminous flux is:
F v ¼ F r 683 ¼ 2192:43 lm
ð2Þ
Now we have to calculate the luminous intensity of the far-field pattern (FFP) and we need to know the N.A. of the optical fiber. It depends on the distance of the optical fiber [11,12]. In the articles of Losada et al. [11,12] for optical fibers longer than 60 m, the asymptotic trend for the exit N.A. is 0.46, corresponding to a full angle of 54.77°. For this angle, the relative intensity is 5%. The luminous intensity in the endface of the optical fiber is:
Iv ¼
Fv
X
¼ 313204:29 cd
ð3Þ
Fig. 1. General scheme of the device. The LED emits a light beam which enters the integrating sphere, and the beam is focused on the endface of the optical fiber.
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Fig. 2. Actual mechanical dimensions of the LED.
Fig. 3. Image of the 200 integrating sphere with one port for the LED and the other for the optical fiber (shaded model).
where X is the solid angle. From Losada et al. [11,12], asymptotically, the kurtosis is 1.5 for optical fiber with a length of more than 40 m. Under these conditions, the best fit for the super-Gaussian is:
h
SG ¼ 0:005 þ 1:005e
x ð16:99 Þ
2
1:15 i
ð4Þ
In Fig. 7, we show the experimental relative intensity with a super-Gaussian fit to know the angular dependence. Fitting the absolute luminous intensity to the experimental relative intensity, we get this super-Gaussian
h i 2 1:15 x ð16:99 Þ SG ¼ 1340:36 þ 1118:35e
ð5Þ
In this way, we can calculate the value of the luminous intensity for every angle. The fit parameters are the following (see Table 1). The residual sum of squares was 8.92191 1029 and the Rsquare coefficient was 1. As can be checked, the fit is excellent, not only because the R-square coefficient is 1, but also because practically all the values of the residuals are in the interval [3 1015, 3 1015]. Fig. 8 shows the results for the multipleregression fit in this interval.
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Fig. 4. Simulation of the irradiance and power injected into the optical fiber.
Fig. 5. General schematic of the device, as well as the situation of the elements for a telecommunication tower.
Our results exceeded the requirements of the ICAO (see Tables 2–4), since we have more than 32 cd (4198 cd). Our beam spread
is 54.77° (more than 10°) and at 10° our intensity is 3853 cd (more than 16 cd).
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Fig. 6. Different height towers with red lights for night (background luminance below 50 cd/m2). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The guidelines of the ICAO require 360° coverage, and therefore, as the intensity in the limit of the N.A. is for 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. The recommendation of the ICAO is 2 low-intensity Type B lamps. If we connect 7 optical fibers to the same integrating sphere, we obtain 2183 cd (more than 32 cd) and at 10° the intensity is 1897 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, making the lamp cheaper and smaller. Each lamp is composed of 1 LED, 1 integrating sphere and 7 optical fibers per integrating sphere. Finally, our 2 lamps will have only 2 LEDs, 2 integrating spheres and 14 optical fibers. The power at the entrance of the endface of the optical fibers is 5.05 W if 1 optical fiber is connected to the integrating sphere, 3.53 W if 2 optical fibers are connected to the integrating sphere, 2.76 W if 3 optical fibers are connected to the integrating sphere, 2.26 W if 4 optical fibers are connected to the integrating sphere, 2.03 W if 5 optical fibers are connected to the integrating sphere, 1.89 W if 6 optical fibers are connected to the integrating sphere
and, 1.81 W if 7 optical fibers are connected to the integrating sphere. These values are obtained with the Zemax simulation. These values are Pi of Eq. (1). The advantage of this new lamp is that we could inject much less current to the LED for less light emission, thereby enormously lengthening the lifetime of the LED.
3.2. Towers of heights up to 52 m The lamp for this tower is similar to those for the 45 m tower. The guidelines of the ICAO (see Tables 2–4) require 360° coverage, and therefore, as the intensity in the limit of the N.A. is 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. As the recommendation of the ICAO is 3 low-intensity Type B lamps, if we connect 7 optical fibers at the same integrating sphere, as in the former height, we obtain 1843 cd (more than 32 cd) and at 10° the intensity is 1395 cd, more than 16 cd, we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller.
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Fig. 7. Experimental FFP of the optical fiber. Super-Gaussian radial pattern with absolute values.
Finally, our 2 lamps will have only 2 LEDs, 2 integrating spheres and 14 optical fibers.
Table 1 Results for the multiple-regression fit.
Losada’s super-Gaussian Our super-Gaussian
Value
Standard error
0.0096 0.00089
2.64025 1016 3.91499 1019
3.3. Towers of heights up to 104 m In the first level (52 m) the results were the same as in the tower discussed above.
Fig. 8. Graph of the residual sum of squares for the multiple-regression fit of the super Gaussian. The fit parameters are from Table 1.
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F. Pérez-Ocón et al. / Engineering Structures 132 (2017) 531–539 Table 2 Characteristics of obstacle lights [8]. Light type
Colour
Signal type/(flash rate)
Peak intensity (cd) at given background luminance (a) Day (above 500 cd/ m2)
Twilight (50–500 cd/ m2)
Night (below 50 cd/ m2)
Light distribution table
Low-intensity Type B (fixed obstacle) Medium-intensity Type B
Red
Fixed
N/A
N/A
32
Table 3
Red
N/A
N/A
2000
Tables 4a and 4b
Medium-intensity Type C
Red
Flashing (20– 60 fpm) Fixed
N/A
N/A
2000/
Tables 4a and 4b
fpm: flashes per minute. (a) For flashing lights, effective intensity as determined in accordance with the Aerodrome Design Manual, Part 4.
Table 3 Light distribution for low intensity obstacle lights [8]. Light type
Type B Type C
Minimum intensity (cd) (a)
Maximum intensity (cd) (a)
32 (b) 40 (b)
N/A 400
Vertical beam spread (c) Minimum beam spread
Intensity (cd)
10° 12°
16 20
(a) 360° horizontal. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Between 2 and 10° vertical. Elevation vertical angles are referenced to the horizontal when the light is leveled. (c) Beam spread is defined as the angle between the horizontal plan and the directions for which the intensity exceeds that mentioned in the ‘‘intensity” column. (d) Peak intensity should be located at approximately 2.5° vertical.
Table 4a Minimum requirements of the light distribution for medium and high intensity obstacle lights according to benchmark intensities of Table 3 [8]. Benchmark intensity (cd)
Minimum requirements Vertical elevation (b)
Vertical beam spread (c) 1°
0°
2000
Minimum average intensity (a)
Minimum average intensity (a)
Minimum average intensity (a)
Minimum beam spread
Intensity (a)
2000
1500
750
3°
750
(a) 360° Horizontal. All intensities are expressed in Candela. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Elevation vertical angles are referenced to the horizontal when the light unit is leveled.
Table 4b Recommendations of the light distribution for medium and high intensity obstacle lights according to benchmark intensities of Table 3 [8]. Benchmark intensity (cd)
Recommendations Vertical elevation angle (b)
2000
Vertical beam spread (c)
0° Maximum intensity (cd) (a)
1° Maximum intensity (cd) (a)
10° Maximum intensity (cd) (a)
Maximum beam spread
Intensity (cd) (a)
2500
1125
75
N/A
N/A
(a) 360° Horizontal. All intensities are expressed in Candela. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Elevation vertical angles are referenced to the horizontal when the light unit is leveled. (c) Beam spread is defined as the angle between the horizontal plan and the directions for which the intensity exceeds that mentioned in the ‘‘intensity” column.
We need a medium-intensity Type C lamp (see the requirements of the ICAO Tables 2–4). Following the recommendations of the ICAO, 2500 cd at 0° is necessary, 1125 cd at 1° and 75 cd at 10°. If we use one LED, one integrating sphere and 4 optical fibers per integrating sphere, we obtain 1362 cd at 0°, 1361 cd at 1° and 1204 cd at 10°. We comply with the recommendations of the ICAO except in the case of 0°. If we use 2 LEDs, 2 integrating spheres and 4 optical fibers per integrating sphere, we will obtain 2724 cd at 0°, 2722 cd at 1° and 2407 cd at 10°. As we have to cover 360°, we need 7 sets, i.e., our lamp for this height would be composed of 14 LEDs, 14 integrating spheres, and 56 optical fibers.
3.4. Towers of heights up to 156 m Up to 104 m the luminaries were the same as in the 104 m tower, with 2 medium-intensity Type C lamps at 104 m, instead of one lamp. The guidelines of the ICAO (see Tables 2–4) require 360° coverage, and therefore, as the intensity in the limit of the N.A. is for 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. As the recommendation of the ICAO is 3 low-intensity Type B lamps, if we connect 7 optical fibers to the same integrating sphere, as in the former height, we obtain 650 cd (more than 32 cd) and at 10° the intensity is 574 cd, more than 16 cd, so we can use only one integrating sphere instead of
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one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps will have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.5. Towers of heights up to 208 m Up to 156 m the luminaries were the same as in the 156 m tower. We need a medium-intensity Type C lamps (see the requirements of the ICAO Tables 2–4). Following the recommendations of the ICAO, 2500 cd at 0° is necessary, 1125 cd at 1° and 75 cd at 10°. If we used one LED, one integrating sphere and one optical fiber per integrating sphere, we obtain 1078 cd at 0°, 1077 cd at 1° and 952 cd at 10°. To comply with the recommendations of the ICAO we need to use 3 sets (LED, integrating sphere, and optical fiber) then we would have 3233 cd at 0°, 3231 cd at 1° and 2857 cd at 10°, more intensity than recommended by the ICAO. As we have to cover 360°, we need 7 sets, i.e., our lamp for this height would be composed of 21 LEDs, 21 integrating spheres, and 21 optical fibers.
To obtain 2622 cd at 0°, 2620 cd at 1°, and 2317 cd at 10° we would have to use 20 LEDs, 20 integrating spheres, and 20 optical fibers. As we need to illuminate 360°, we have to use seven columns of the set above. Therefore, we would have to use 140 LEDs, 140 integrating spheres and 140 optical fibers. 3.10. Towers of heights up to 468 m Up to 416 m the luminaries were the same as in the 416 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 4 optical fibers at the same integrating sphere, we would obtain 34 cd (more than 32 cd) and at 10° the intensity is 30 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. As we need to illuminate 360°, we have to use at least, seven optical fibers, i.e., 2 sets as calculated to cover the circumferences. Finally, our 3 lamps would have only 6 LEDs, 6 integrating spheres and 24 optical fibers.
3.6. Towers of heights up to 260 m 3.11. Towers of heights of up to 520 m Up to 208 m the luminaries were the same as in the 208 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of the ICAO, if we connect 7 optical fibers at the same integrating sphere, we would obtain 228 cd (more than 32 cd) and at 10° the intensity is 202 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps would have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.7. Towers of heights up to 312 m Up to 260 m the luminaries were the same as in the 260 m tower. At 312 m the luminary was 1 medium-intensity Type C lamp (see Tables 2–4). To obtain 2657 cd at 0°, 2655 cd at 1°, and 2348 cd at 10° we would have to use 7 LEDs, 7 integrating spheres, and 7 optical fibers per sphere. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we have to use 49 LEDs, 49 integrating spheres and 49 optical fibers. 3.8. Towers of heights up to 364 m Up to 312 m the luminaries were the same as in the 312 m tower but with 2 lamps at the top. We need 3 Low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 7 optical fibers at the same integrating sphere, we would obtain 79 cd (more than 32 cd) and at 10° the intensity is 70 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps would have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.9. Towers of heights up to 416 m Up to 364 m, the luminary was the same as in the 364 m tower. At 416 m, one medium-intensity Type C lamp was necessary (see Tables 2–4).
Up to 468 m, the luminary was the same as in the 468 m tower. At 520 m, one medium-intensity Type C lamp is necessary (see Tables 2–4). To obtain 2510 cd at 0°, 2508 cd at 1°, and 2218 cd at 10° we would have to use 55 LEDs, 55 integrating spheres, and 55 optical fibers. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we would have to use 385 LEDs, 385 integrating spheres and 385 optical fibers. 3.12. Towers of heights of up to 572 m Up to 520 m the luminaries were the same as in the 520 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 1 optical fiber at the same integrating sphere, we would not obtain the necessary intensity recommended for the ICAO. For this, we need to use a column of 2 LEDs, 2 integrating spheres and 2 optical fibers and we get 53 cd (more than 32 cd) and at 10° the intensity is 46 cd, more than 16 cd. As we need to illuminate 360°, we have to use seven columns of the set above; therefore, we have to use 14 LEDs, 14 integrating spheres and 14 optical fibers. As 3 lamps are necessary, the total number of components is 42 LEDs, 42 integrating spheres and 42 optical fibers. 3.13. Towers of heights of up to 624 m Up to 572 m, the luminary was the same as in the 572 m tower. At 624 m, one medium-intensity Type C lamp is necessary (see Tables 2–4). To obtain 2502 cd at 0°, 2500 cd at 1°, and 2211 cd at 10° we would have to use 162 LEDs, 162 integrating spheres, and 162 optical fibers. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we would have to use 1134 LEDs, 1134 integrating spheres and 1134 optical fibers. In our design, we have proposed the use of LEDs in all cases instead of lasers because LEDs are cheaper than lasers. In addition, our new LED lamps can be used as low-intensity, Type A and Type B, medium-intensity Type C (fixed light) or medium-intensity Type B (flashing 20–60 fpm). If the lamps are made by laser, it would be difficult to obtain 20–60 frames per minute because the laser mod-
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ulation would be light/no light. This kind of modulation can be carried out easily. In direct modulation, we act directly on the power supply of the laser to obtain modulation on/off at the exit of the laser, i.e., we obtain a binary modulation (0/1). Furthermore, the chirp (change in the frequency of the laser) is a big problem in this kind of modulation. Moreover, the lifetime of the laser diminishes enormously. LEDs support the on/off better than lasers do.
539
Current beacons on high towers weigh around 11.7 kg, so the weight could reach as much as 290 kg, whereas in our case this weight is eliminated. Finally, our obstruction lighting system constitutes a major improvement in safety, not only to air traffic, but also for workers, as no technician has to climb 45–624 m to repair a beacon. References
4. Conclusions We have designed a new obstruction lighting system for aviation safety. In our device, the luminous source lies at the base and the light rises to any point of a telecommunication tower, pole, chimney, stack, and skeletal structures by travelling through a bundle of optical fibers. The light beam of the LED array is concentrated and focused onto the endface of the optical fibers with integrating spheres, thereby providing light to the top of the structure despite the loss in the optical fibers. This new design is a significant improvement in the maintenance of the towers and similar structures because silica optical fibers are highly resistant to natural phenomena, and they are also robust, flexible, reliable, maintenance free, low cost, and durable with the passage of the time; they are better than the POFs because the degradation of POFs are faster than the silica optical fibers. The added optical fibers and integrating spheres do not alter the signalling because they comply rigorously with international safety guidelines of ICAO. The operation temperature of our lamps complies with the international guidelines of the ICAO; moreover, to operate in the Arctic, the optical fibers and the integrating spheres comply with the guidelines. LEDs at the top of the towers can create electromagnetic interferences because they generate small magnetic and electric fields near the antennas. Now, above the tower there are optical fibers which do not create electromagnetic fields out of the optical fibers.
[1] Kerr JR. Enhanced detection of LED runway/approach lights for EVS. Proc SPIE 2008;6957:695703. [2] Lu W, Zhang T, He SM, Zhang B, Li N, Liu SS. Light-emitting diodes for space applications. Opt Quant Electron 2009;41(11–13):883–93. [3] Petrick JT. High-brightness LEDs in aerospace applications. Proc SPIE 2002;4776:34–50. [4] González Montes M, Vázquez D, Fernández-Balbuena AA, Bernabeu E. Beacon system based on light-emitting diode sources for runways lighting. Opt Eng 2014;53(6):066104. [5] Pérez-Ocón F, Pozo AM, Rubiño M, Rabaza O. Safer and innovative traffic lights with minilenses and optical fibers. Eng Struct 2015;96:1–6. [6] Pérez-Ocón F, Rubiño M, Pozo AM, Rabaza O. Design of new traffic lights: traffic safety and maintenance ease. Eng Struct 2013;57:388–92. [7] ICAO (International Civil Aviation Organization). International standards and recommended practices, Annex 14 to the convention on international civil aviation, aerodromes, vol. I. Aerodrome design and operations. 6th ed.; July 2013. [8] ICAO (International Civil Aviation Organization), The first meeting of the Apanpirg aerodromes operations and planning-working group (AOP/WG/1), Bangkok, Thailand, 21–23 May 2013, Amendment 11 to Annex 14, vol. I – aerodrome design and operations; 2013. [9] FAA (Federal Aviation Administration). US Department of Transportation. Advisory Circular No: 150/5345-43G. Specification for obstruction lighting equipment. Indicated by Airport Safety and Standards 100. 9/26/2012. [10] Appajaiah A, Kretzschmar H-J, Daum W. Aging behavior of polymer optical fibers: degradation characterization by FTIR. J Appl Polym Sci 2007;10 (2):860–70. doi: http://dx.doi.org/10.1002/app.25214. [11] Losada MA, Mateo J, Espinosa D, Garcés I, Zubia J. Characterization of the far field pattern for plastic optical fibers. Int Conf Plast Opt Fibers Appl 2004;13:458–65. [12] Mateo J, Losada MA, Garcés I, Zubia J. Global characterization of optical power propagation in step-index plastic optical fibers. Opt Express 2006;14:9028–35. doi: http://dx.doi.org/10.1364/OE.14.009028.
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Engineering Structures journal homepage: www.elsevier.com/locate/engstruct
New obstruction lighting system for aviation safety F. Pérez-Ocón a,⇑, A.M. Pozo a, O. Rabaza b a b
Department of Optics, University of Granada, Granada 18071, Spain Department of Civil Engineering, University of Granada, Granada 18071, Spain
a r t i c l e
i n f o
Article history: Received 5 October 2015 Revised 18 November 2016 Accepted 21 November 2016
Keywords: Beacon Repair Maintenance ease Work safety Availability LEDs Integrating spheres Optical fibers
a b s t r a c t Signposting and illuminating obstacles is meant to reduce risks to aircraft by aiding the pilot in locating dangers. However, many of the obstacles to air transport, such as telecommunication towers, can surpass heights of 45 m. This implies that the installation or repair of the beacon system can involve serious risks to the personnel in charge of such work, as the tower must be climbed with the use of harnesses, helmets, and other means of protection with the hazards that these involve. To avoid these drawbacks, in this study we have designed an obstruction lighting system in which the light source lies at the base of the structure and the light, travelling through a bundle of optical fibers, rises to any point of the telecommunication tower, pole, chimney, stack or similar skeletal structures. Therefore, the proposed system would provide a major improvement in safety, not only for air traffic, but also for workers. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The rapid development of LEDs (light-emitting diodes) as new sources of light emission have made them the current light indicators in electronic devices and systems, light-signalling systems, and exterior and interior illumination systems. As the characteristics of LEDs have improved with the introduction of new manufacturing and design technology, in-depth studies have been made regarding the application of these as signalling and illumination systems in general [1–6]. These studies have been made by companies which specialize in the manufacture of illumination systems based on LED technology, such as traffic lights and street lights. Illumination systems with LEDs constitute an effective and lowcost alternative for signalling fixed obstacles (chimneys, telecommunication towers, high buildings, etc.) and even mobile ones, although the position of these signalling devices, as with conventional beacons, poses problems. The signalling and illumination of obstacles is intended to lower the risks for aircraft, as it helps the pilot to locate potential dangers. This does not necessarily diminish the limitations of operation imposed by an obstacle, but when it is not possible to ⇑ Corresponding author at: Department of Optics, Science Faculty, Edificio Mecenas, Campus Universitario de Fuentenueva, University of Granada, 18071 Granada, Spain. E-mail address: [email protected] (F. Pérez-Ocón). http://dx.doi.org/10.1016/j.engstruct.2016.11.054 0141-0296/Ó 2016 Elsevier Ltd. All rights reserved.
eliminate the obstacle and it does not affect the safety or regularity of air service, the obstacle should be properly signposted and illuminated to be seen clearly by pilots under any weather and visibility conditions. Markers displayed on or adjacent to objects shall be located in conspicuous positions so as to retain the general definition of the object and shall be recognizable in clear weather from a distance of at least 1000 m for an object to be viewed from the air and 300 m for an object to be viewed from the ground in all directions in which an aircraft is likely to approach the object [7]. It should be taken into account that many of the obstacles for air transport, such as telecommunication towers, high-voltage towers, or wind turbines can reach heights of more than 45 m. This implies that the installation or repair of any beacon system can involve serious risks to the workers in charge of these tasks, as the tower must be climbed with harnesses, helmets and other protective devices that in themselves represent hazards and discomfort for the worker. In addition, the tools used (usually heavy) can fall from considerable heights and injure operators at the foot of the tower. Furthermore, the beacons of the telecommunication towers can weigh between 5 and 20 kg, so that a 300 m-high tower with 14 beacons could bear weights of more than 280 kg in light signalling alone. To avoid the above drawbacks, in this study we have designed an obstruction lighting system for fixed obstacles. The new system consists of placing a LED matrix at the bottom of the obstacle; by
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means of integrating spheres and optical fibers, the light is conducted from the bottom to the top of the structure that needs to be illuminated. In this way, when it is necessary to make a repair, operators do not have to climb the structure, since the repair is made on the ground. Finally, we have calculated the parameters of the new obstruction lighting system that meets the International Civil Aviation Organization (ICAO) lighting requirements [7,8]. 2. Materials: LEDs, integrating spheres, and optical fibers In this study, we have used materials that comply with the rules of the FAA (Federal Aviation Administration) of the U.S. Department of Transportation [9], which are more restrictive than international regulations in terms of working at certain temperatures and humidity, etc. 2.1. Red LED For the design of the system, we propose an encapsulated LED that permits the formation of matrices in a practical, convenient way. The LED, chosen for its characteristics, was SST-90-R LEDs from Luminus Devices, Inc. This LED is used in many applications, for instance, as beacons and obstruction lighting. The LED emission area is 9 mm2, the luminous flux is 1500 lm at 9 A, the radiant efficacy at this wavelength is 269.0 lm/W, and the dominant wavelength 618 nm. It has a DC forward voltage of 2.5 V (system operating on DC volts 24–48 V [9]), a DC forward intensity current of 350 mA (current 75–500 mA [9]), an operating temperature of between 40 °C and 120 °C (40° to 55 °C [9]), and a limit maintained temperature of 217 °C. 2.2. Integrating sphere To collect all the luminous flux which exits the LED into the optical fiber, we have incorporated an integrating sphere into our design. The 200 (50.8 mm diameter) sphere used are from Edmund Optics Ltd. The reason for using this device is to collect the spatial radiant flux in order to spatially integrate the flux to maximize its injection into the optical fiber. The sphere is coupled with the LED in a port, and in a second port in front of it, we couple the optical fiber with a SMA connector to inject as much light as possible within the optical fiber. The inner reflectance of the integrating sphere is 0.95. 2.3. Optical fiber The optical fiber proposed is the FV100010501250 from Polymicro TechnologiesTM. The core diameter, cladding, and buffer are 1 mm, 1.05 mm, and 1.25 mm, respectively. It is an optical fiber with a profile-step index, high AOH silica core, doped silica clad, and high-temperature acrylate buffer. The optical fiber can operate between 65 °C and 300 °C (intermittently up to 400 °C). It has a numerical aperture of 0.22 and its full acceptance cone is 25.4°. The attenuation is 30, 15, and 10 dB/km around 457, 586 and 630 nm, respectively. A silica optical fiber was chosen because the degradation is less than for plastic optical fiber (POF) [10]. The LED emits a light beam which enters the integrating sphere and then the light enters the endface of the optical fiber (changing the refractive index); at the exit, again, there is a change in the refractive index, from optical fiber to air. Therefore, it is essential to take into account the Fresnel reflection loss twice. The calculated Fresnel reflection loss is 0.74 dB.
3. Results and discussion The general scheme is shown in Fig. 1. More specifically, we have developed our design for a telecommunication tower, although it could be applied to any fixed structure mentioned in Annex 14 of the Convention on International Civil Aviation [7,8]. As mentioned in Section 2.3, the LED emits a light beam which enters the integrating sphere and then the light enters the endface of the optical fiber. Therefore, it is essential to take into account the Fresnel reflection loss due to the change in the refractive index. The calculated Fresnel reflection loss is 0.74 dB. We have simulated all the radiation process with Zemax-EE V. 2005. Dimensions of the LED are shown in Fig. 2. We then modelled the integrating sphere with Zemax in the same way. Fig. 3 shows the shaded model of the 200 integrating spheres. Fig. 4 shows the power injected into the optical fiber at the exit of the integrating sphere. The peak of irradiance is 5.22 W/cm2 and the total power 5.05 W. Fig. 5 shows the general schematic of the device, as well as the situation of the elements for a telecommunication tower. Following the amendment 11 to Annex 14 [8], for poles, radio, and television towers and similar skeletal structures, the light must be type B fixed of low-intensity and type C fixed of medium-intensity. We present the results for the different heights in Fig. 6. 3.1. Tower up to 45 m The power at the endface of one optical fiber is:
Po ¼ P i eaL AF ¼ 3:21 W
ð1Þ
where Pi is the entrance power in the optical fiber, a is the attenuation coefficient, L the length of the optical fiber for tower up to 45 m, and AF is the Fresnel reflection attenuation. The luminous flux is:
F v ¼ F r 683 ¼ 2192:43 lm
ð2Þ
Now we have to calculate the luminous intensity of the far-field pattern (FFP) and we need to know the N.A. of the optical fiber. It depends on the distance of the optical fiber [11,12]. In the articles of Losada et al. [11,12] for optical fibers longer than 60 m, the asymptotic trend for the exit N.A. is 0.46, corresponding to a full angle of 54.77°. For this angle, the relative intensity is 5%. The luminous intensity in the endface of the optical fiber is:
Iv ¼
Fv
X
¼ 313204:29 cd
ð3Þ
Fig. 1. General scheme of the device. The LED emits a light beam which enters the integrating sphere, and the beam is focused on the endface of the optical fiber.
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Fig. 2. Actual mechanical dimensions of the LED.
Fig. 3. Image of the 200 integrating sphere with one port for the LED and the other for the optical fiber (shaded model).
where X is the solid angle. From Losada et al. [11,12], asymptotically, the kurtosis is 1.5 for optical fiber with a length of more than 40 m. Under these conditions, the best fit for the super-Gaussian is:
h
SG ¼ 0:005 þ 1:005e
x ð16:99 Þ
2
1:15 i
ð4Þ
In Fig. 7, we show the experimental relative intensity with a super-Gaussian fit to know the angular dependence. Fitting the absolute luminous intensity to the experimental relative intensity, we get this super-Gaussian
h i 2 1:15 x ð16:99 Þ SG ¼ 1340:36 þ 1118:35e
ð5Þ
In this way, we can calculate the value of the luminous intensity for every angle. The fit parameters are the following (see Table 1). The residual sum of squares was 8.92191 1029 and the Rsquare coefficient was 1. As can be checked, the fit is excellent, not only because the R-square coefficient is 1, but also because practically all the values of the residuals are in the interval [3 1015, 3 1015]. Fig. 8 shows the results for the multipleregression fit in this interval.
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Fig. 4. Simulation of the irradiance and power injected into the optical fiber.
Fig. 5. General schematic of the device, as well as the situation of the elements for a telecommunication tower.
Our results exceeded the requirements of the ICAO (see Tables 2–4), since we have more than 32 cd (4198 cd). Our beam spread
is 54.77° (more than 10°) and at 10° our intensity is 3853 cd (more than 16 cd).
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Fig. 6. Different height towers with red lights for night (background luminance below 50 cd/m2). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The guidelines of the ICAO require 360° coverage, and therefore, as the intensity in the limit of the N.A. is for 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. The recommendation of the ICAO is 2 low-intensity Type B lamps. If we connect 7 optical fibers to the same integrating sphere, we obtain 2183 cd (more than 32 cd) and at 10° the intensity is 1897 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, making the lamp cheaper and smaller. Each lamp is composed of 1 LED, 1 integrating sphere and 7 optical fibers per integrating sphere. Finally, our 2 lamps will have only 2 LEDs, 2 integrating spheres and 14 optical fibers. The power at the entrance of the endface of the optical fibers is 5.05 W if 1 optical fiber is connected to the integrating sphere, 3.53 W if 2 optical fibers are connected to the integrating sphere, 2.76 W if 3 optical fibers are connected to the integrating sphere, 2.26 W if 4 optical fibers are connected to the integrating sphere, 2.03 W if 5 optical fibers are connected to the integrating sphere, 1.89 W if 6 optical fibers are connected to the integrating sphere
and, 1.81 W if 7 optical fibers are connected to the integrating sphere. These values are obtained with the Zemax simulation. These values are Pi of Eq. (1). The advantage of this new lamp is that we could inject much less current to the LED for less light emission, thereby enormously lengthening the lifetime of the LED.
3.2. Towers of heights up to 52 m The lamp for this tower is similar to those for the 45 m tower. The guidelines of the ICAO (see Tables 2–4) require 360° coverage, and therefore, as the intensity in the limit of the N.A. is 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. As the recommendation of the ICAO is 3 low-intensity Type B lamps, if we connect 7 optical fibers at the same integrating sphere, as in the former height, we obtain 1843 cd (more than 32 cd) and at 10° the intensity is 1395 cd, more than 16 cd, we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller.
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Fig. 7. Experimental FFP of the optical fiber. Super-Gaussian radial pattern with absolute values.
Finally, our 2 lamps will have only 2 LEDs, 2 integrating spheres and 14 optical fibers.
Table 1 Results for the multiple-regression fit.
Losada’s super-Gaussian Our super-Gaussian
Value
Standard error
0.0096 0.00089
2.64025 1016 3.91499 1019
3.3. Towers of heights up to 104 m In the first level (52 m) the results were the same as in the tower discussed above.
Fig. 8. Graph of the residual sum of squares for the multiple-regression fit of the super Gaussian. The fit parameters are from Table 1.
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F. Pérez-Ocón et al. / Engineering Structures 132 (2017) 531–539 Table 2 Characteristics of obstacle lights [8]. Light type
Colour
Signal type/(flash rate)
Peak intensity (cd) at given background luminance (a) Day (above 500 cd/ m2)
Twilight (50–500 cd/ m2)
Night (below 50 cd/ m2)
Light distribution table
Low-intensity Type B (fixed obstacle) Medium-intensity Type B
Red
Fixed
N/A
N/A
32
Table 3
Red
N/A
N/A
2000
Tables 4a and 4b
Medium-intensity Type C
Red
Flashing (20– 60 fpm) Fixed
N/A
N/A
2000/
Tables 4a and 4b
fpm: flashes per minute. (a) For flashing lights, effective intensity as determined in accordance with the Aerodrome Design Manual, Part 4.
Table 3 Light distribution for low intensity obstacle lights [8]. Light type
Type B Type C
Minimum intensity (cd) (a)
Maximum intensity (cd) (a)
32 (b) 40 (b)
N/A 400
Vertical beam spread (c) Minimum beam spread
Intensity (cd)
10° 12°
16 20
(a) 360° horizontal. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Between 2 and 10° vertical. Elevation vertical angles are referenced to the horizontal when the light is leveled. (c) Beam spread is defined as the angle between the horizontal plan and the directions for which the intensity exceeds that mentioned in the ‘‘intensity” column. (d) Peak intensity should be located at approximately 2.5° vertical.
Table 4a Minimum requirements of the light distribution for medium and high intensity obstacle lights according to benchmark intensities of Table 3 [8]. Benchmark intensity (cd)
Minimum requirements Vertical elevation (b)
Vertical beam spread (c) 1°
0°
2000
Minimum average intensity (a)
Minimum average intensity (a)
Minimum average intensity (a)
Minimum beam spread
Intensity (a)
2000
1500
750
3°
750
(a) 360° Horizontal. All intensities are expressed in Candela. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Elevation vertical angles are referenced to the horizontal when the light unit is leveled.
Table 4b Recommendations of the light distribution for medium and high intensity obstacle lights according to benchmark intensities of Table 3 [8]. Benchmark intensity (cd)
Recommendations Vertical elevation angle (b)
2000
Vertical beam spread (c)
0° Maximum intensity (cd) (a)
1° Maximum intensity (cd) (a)
10° Maximum intensity (cd) (a)
Maximum beam spread
Intensity (cd) (a)
2500
1125
75
N/A
N/A
(a) 360° Horizontal. All intensities are expressed in Candela. For flashing lights, the intensity is read into effective intensity, as determined in accordance with the Aerodrome Design Manual, Part 4. (b) Elevation vertical angles are referenced to the horizontal when the light unit is leveled. (c) Beam spread is defined as the angle between the horizontal plan and the directions for which the intensity exceeds that mentioned in the ‘‘intensity” column.
We need a medium-intensity Type C lamp (see the requirements of the ICAO Tables 2–4). Following the recommendations of the ICAO, 2500 cd at 0° is necessary, 1125 cd at 1° and 75 cd at 10°. If we use one LED, one integrating sphere and 4 optical fibers per integrating sphere, we obtain 1362 cd at 0°, 1361 cd at 1° and 1204 cd at 10°. We comply with the recommendations of the ICAO except in the case of 0°. If we use 2 LEDs, 2 integrating spheres and 4 optical fibers per integrating sphere, we will obtain 2724 cd at 0°, 2722 cd at 1° and 2407 cd at 10°. As we have to cover 360°, we need 7 sets, i.e., our lamp for this height would be composed of 14 LEDs, 14 integrating spheres, and 56 optical fibers.
3.4. Towers of heights up to 156 m Up to 104 m the luminaries were the same as in the 104 m tower, with 2 medium-intensity Type C lamps at 104 m, instead of one lamp. The guidelines of the ICAO (see Tables 2–4) require 360° coverage, and therefore, as the intensity in the limit of the N.A. is for 54.77°, we need 7 optical fibers at the top of the tower, each covering a solid angle of 0.70 sr. As the recommendation of the ICAO is 3 low-intensity Type B lamps, if we connect 7 optical fibers to the same integrating sphere, as in the former height, we obtain 650 cd (more than 32 cd) and at 10° the intensity is 574 cd, more than 16 cd, so we can use only one integrating sphere instead of
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one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps will have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.5. Towers of heights up to 208 m Up to 156 m the luminaries were the same as in the 156 m tower. We need a medium-intensity Type C lamps (see the requirements of the ICAO Tables 2–4). Following the recommendations of the ICAO, 2500 cd at 0° is necessary, 1125 cd at 1° and 75 cd at 10°. If we used one LED, one integrating sphere and one optical fiber per integrating sphere, we obtain 1078 cd at 0°, 1077 cd at 1° and 952 cd at 10°. To comply with the recommendations of the ICAO we need to use 3 sets (LED, integrating sphere, and optical fiber) then we would have 3233 cd at 0°, 3231 cd at 1° and 2857 cd at 10°, more intensity than recommended by the ICAO. As we have to cover 360°, we need 7 sets, i.e., our lamp for this height would be composed of 21 LEDs, 21 integrating spheres, and 21 optical fibers.
To obtain 2622 cd at 0°, 2620 cd at 1°, and 2317 cd at 10° we would have to use 20 LEDs, 20 integrating spheres, and 20 optical fibers. As we need to illuminate 360°, we have to use seven columns of the set above. Therefore, we would have to use 140 LEDs, 140 integrating spheres and 140 optical fibers. 3.10. Towers of heights up to 468 m Up to 416 m the luminaries were the same as in the 416 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 4 optical fibers at the same integrating sphere, we would obtain 34 cd (more than 32 cd) and at 10° the intensity is 30 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. As we need to illuminate 360°, we have to use at least, seven optical fibers, i.e., 2 sets as calculated to cover the circumferences. Finally, our 3 lamps would have only 6 LEDs, 6 integrating spheres and 24 optical fibers.
3.6. Towers of heights up to 260 m 3.11. Towers of heights of up to 520 m Up to 208 m the luminaries were the same as in the 208 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of the ICAO, if we connect 7 optical fibers at the same integrating sphere, we would obtain 228 cd (more than 32 cd) and at 10° the intensity is 202 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps would have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.7. Towers of heights up to 312 m Up to 260 m the luminaries were the same as in the 260 m tower. At 312 m the luminary was 1 medium-intensity Type C lamp (see Tables 2–4). To obtain 2657 cd at 0°, 2655 cd at 1°, and 2348 cd at 10° we would have to use 7 LEDs, 7 integrating spheres, and 7 optical fibers per sphere. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we have to use 49 LEDs, 49 integrating spheres and 49 optical fibers. 3.8. Towers of heights up to 364 m Up to 312 m the luminaries were the same as in the 312 m tower but with 2 lamps at the top. We need 3 Low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 7 optical fibers at the same integrating sphere, we would obtain 79 cd (more than 32 cd) and at 10° the intensity is 70 cd, more than 16 cd, so we can use only one integrating sphere instead of one for each optical fiber, thus making the lamp cheaper and smaller. Finally, our 3 lamps would have only 3 LEDs, 3 integrating spheres and 21 optical fibers. 3.9. Towers of heights up to 416 m Up to 364 m, the luminary was the same as in the 364 m tower. At 416 m, one medium-intensity Type C lamp was necessary (see Tables 2–4).
Up to 468 m, the luminary was the same as in the 468 m tower. At 520 m, one medium-intensity Type C lamp is necessary (see Tables 2–4). To obtain 2510 cd at 0°, 2508 cd at 1°, and 2218 cd at 10° we would have to use 55 LEDs, 55 integrating spheres, and 55 optical fibers. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we would have to use 385 LEDs, 385 integrating spheres and 385 optical fibers. 3.12. Towers of heights of up to 572 m Up to 520 m the luminaries were the same as in the 520 m tower but with 2 lamps at the top. We need 3 low-intensity Type B lamps (see the requirements of the ICAO Tables 2–4). Following the recommendation of ICAO, if we connect 1 optical fiber at the same integrating sphere, we would not obtain the necessary intensity recommended for the ICAO. For this, we need to use a column of 2 LEDs, 2 integrating spheres and 2 optical fibers and we get 53 cd (more than 32 cd) and at 10° the intensity is 46 cd, more than 16 cd. As we need to illuminate 360°, we have to use seven columns of the set above; therefore, we have to use 14 LEDs, 14 integrating spheres and 14 optical fibers. As 3 lamps are necessary, the total number of components is 42 LEDs, 42 integrating spheres and 42 optical fibers. 3.13. Towers of heights of up to 624 m Up to 572 m, the luminary was the same as in the 572 m tower. At 624 m, one medium-intensity Type C lamp is necessary (see Tables 2–4). To obtain 2502 cd at 0°, 2500 cd at 1°, and 2211 cd at 10° we would have to use 162 LEDs, 162 integrating spheres, and 162 optical fibers. As we need to illuminate 360°, we would have to use seven columns of the set above. Therefore, we would have to use 1134 LEDs, 1134 integrating spheres and 1134 optical fibers. In our design, we have proposed the use of LEDs in all cases instead of lasers because LEDs are cheaper than lasers. In addition, our new LED lamps can be used as low-intensity, Type A and Type B, medium-intensity Type C (fixed light) or medium-intensity Type B (flashing 20–60 fpm). If the lamps are made by laser, it would be difficult to obtain 20–60 frames per minute because the laser mod-
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ulation would be light/no light. This kind of modulation can be carried out easily. In direct modulation, we act directly on the power supply of the laser to obtain modulation on/off at the exit of the laser, i.e., we obtain a binary modulation (0/1). Furthermore, the chirp (change in the frequency of the laser) is a big problem in this kind of modulation. Moreover, the lifetime of the laser diminishes enormously. LEDs support the on/off better than lasers do.
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Current beacons on high towers weigh around 11.7 kg, so the weight could reach as much as 290 kg, whereas in our case this weight is eliminated. Finally, our obstruction lighting system constitutes a major improvement in safety, not only to air traffic, but also for workers, as no technician has to climb 45–624 m to repair a beacon. References
4. Conclusions We have designed a new obstruction lighting system for aviation safety. In our device, the luminous source lies at the base and the light rises to any point of a telecommunication tower, pole, chimney, stack, and skeletal structures by travelling through a bundle of optical fibers. The light beam of the LED array is concentrated and focused onto the endface of the optical fibers with integrating spheres, thereby providing light to the top of the structure despite the loss in the optical fibers. This new design is a significant improvement in the maintenance of the towers and similar structures because silica optical fibers are highly resistant to natural phenomena, and they are also robust, flexible, reliable, maintenance free, low cost, and durable with the passage of the time; they are better than the POFs because the degradation of POFs are faster than the silica optical fibers. The added optical fibers and integrating spheres do not alter the signalling because they comply rigorously with international safety guidelines of ICAO. The operation temperature of our lamps complies with the international guidelines of the ICAO; moreover, to operate in the Arctic, the optical fibers and the integrating spheres comply with the guidelines. LEDs at the top of the towers can create electromagnetic interferences because they generate small magnetic and electric fields near the antennas. Now, above the tower there are optical fibers which do not create electromagnetic fields out of the optical fibers.
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