Aviation Obstruction Light

Table of Contents

  1. Types of lights
  2. Comparison of GLS and LED Lamps

High-rise buildings and structures such as chimneys, towers and smoke stacks are potential hazards to aircraft. As such mandatory provisions are in force for providing AOL's for hazard indication on structures above 6 m in height.

Requirements: The International Civil Aviation Organization (IACO) specifies two main requirements (ICAO Standards, annexure 14, Vol 1, Chapter 6) of aviation obstruction lights:

  1. Height, number and location of lights.
  2. Light intensity.

The following are the type of AOL's required depending on the height:

Types of lights

  1. GLS Lamps: Usually 100W lamps are used. The standard GLS lamps have an average burning life of 1000 hours and a MSCP (mean spherical candle power) of 100 cd. As these lamps emit white light and red wavelength is only one seventh of total colour spectrum, effective MSCP is only about 12 cd. They are also very sensitive to voltage fluctuation and are susceptible to over voltages during the night in upcountry. The fragile filament can break early due to high wind velocity. Also, the soft glass dome lens provided in these AOL's gets extremely hot and tends to crack in rain. The rubber gasket of these AOL's also tends to get damaged due to heat, allowing water ingress. Even all things being good, considering 12 hours usage, the bulb needs to be replaced every three months. At extreme heights (such as in industrial chimneys), this is hazardous and complicated procedure, involving additional expenses due to the nature of job.

    To ensure fail safe operation, twin lamps are normally provided. For medium intensity AOL's, double light fitting is only used and used 500 to 650 W lamps.

  2. Neon Spiral (GEC) Discharge Tubes: These have improved illumination and increased life as compared with GLS lamps. But they suffer from the disadvantage that the high voltage transformer (3 kV) is very costly and is not available of reliable quality in India. As such they have a high failure rate and do not last even to their specified life of 5 000 hours. Finally higher wattage and low power factor of the transformer leads to increased operating cost. Also while changing tubes at such heights, technicians are not able to fix properly, resulting in water seepage and failure of the transformer.

  3. LED Lamps: These are most suitable for aviation lights, even though costly. They have long life (1 00 000 hours), low power consumption (5 to 15 W for low intensity, 25 W for medium intensity), reliable due to multiple circuits, shock-proof, improved power factor and able to withstand voltage fluctuations of ±25 %. Furthermore, they eliminate possibility of non-compliance from aviation authorities due to failed lamp.

Comparison of GLS and LED Lamps

 GLSLEDLED (90 cd)Remark
Lighting performance10 cd18 cd90 cdICAO minimum: 10 cd
Power consumption100 W5 W15 WGLS need twin for redundancy
Average lamp life (h)1 000 h (~ 3 months average)1 00 000 h (~ 20 years average) - do - 12 h/day

Initial investment in LED obstacle lights is approximately 25 % to 50 % more expensive than the imported GLS and locally made GLS respectively. However, with almost zero maintenance cost and very low power consumption, LED has a swift payback period of only 6 months compared to the imported GLS and 11 months to the locally made GLS. Moreover, 5 years NPV cash flow (9 % interest rate) of the imported and locally made GLS are both way higher than the initial investment.

As each tower must install up to 4 obstacle lights, depending on the height, it would mean a market of 8 000 to 12 000 obstacle lights and significant savings can be made by providing LED lamps.


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