The Federal Aviation Administration (FAA) requires that obstructions to aircraft navigation, such as towers, cables and tall buildings be fitted with visibly perceivable elements to render these structures highly visible to approaching aircraft. FAA Advisory Circular 150/5345-43 forms a specification of technical requirements for these lights in the United States.
Within Advisory Circular 150/5345-43 there exists a requirement for a low-intensity, steady-burn red light system, designated the “L-810,” to be placed in accordance with a set plan at levels on all obstructions that are potential hazards to air navigation. The L-810 lighting system generally incorporates a light source and a lensed dome that directs red light into a 360 azimuth around the obstruction and within a minimum vertical beam spread of 10 degrees about a plane anywhere from 4 to 20 degrees above the horizontal. The minimum intensity of the L-810 light is 32.5 candela.
A conventional L-810 obstruction light employs an incandescent lamp. The lensed dome comprises a red filter glass structure having a molded Fresnel outer portion and a lenticular array inner portion. Substantially white light produced by a filament of the incandescent lamp is focused vertically into the 10-degree zone by the Fresnel portion and is dispersed uniformly into the 360-degree zone by the lenticular array portion.
A weak link in conventional L-810 lighting systems is the incandescent lamp, which has a relatively limited service life. Consequently, the incandescent lamp requires frequent replacement. Since L-810 obstruction lights are normally mounted atop tall structures, replacing these lamps can be inconvenient, time-consuming, expensive and even dangerous.
Advisory Circular 150/5345-43 also requires that obstruction lights be monitored for proper operation. Although such monitoring can be accomplished manually by regularly visually observing the obstruction lights, manual monitoring can be laborious and inconvenient, particularly when an obstruction or a network of obstructions, such as a wind turbine electric power generation field, utilizes a number of obstruction lights. Consequently, automatic remote monitoring systems are often utilized to monitor the obstruction lights and sound an alarm to maintenance personnel in the event of a failure. Light sensors, such as photocells, can be used to monitor light output. However, light sensors suffer from several drawbacks, principally the complexity of the circuitry required to sound an alarm to maintenance personnel who are located at a distance from a failed obstruction light. Thus, remote monitoring of the light by monitoring the power consumption characteristics of the obstruction light is preferred. In such arrangements the power consumption of an obstruction light is monitored, the power consumption falling to a lower level in the event of a lamp failure. However, remote monitoring of the obstruction light in this manner is problematic due to the difficulty in accurately monitoring the power consumption characteristics of an obstruction light having a much lower current (i.e., light emitting diode vs. incandescent light sources) or comparatively high quiescent currents from the light emitting diode ballast and/or system wiring capacitance.
Another drawback of conventional obstruction lights is light pollution. Light pollution as it relates to obstruction lighting may be generally defined as the emission of light outside the band specified by Advisory Circular 150/5345-43. Light pollution can be an annoyance, particularly when the obstruction light is proximate to residential areas. In some cases light pollution can cause problems such as sleep deprivation or the blocking of an evening view.
There exists a need for an obstruction lighting system that meets the requirements of Advisory Circular 150/5345-43 and uses light sources having a higher reliability than is available with incandescent lamps. There is a further need for an obstruction lighting system that is easily configured for remote fault monitoring and that effectively confines light emissions to desired lighting patterns.