There are many advantages that LEDs offer for use in general illumination. The use of LEDs in certain applications can provide improved energy efficiency. For example, in traffic lights in the United States, LED technology has taken over the market not only because of the energy savings as compared to standard incandescents, but also because of the reduced maintenance costs associated with bulb replacement and improved reliability. With useful lifetimes exceeding 40,000 hours or more, today's high flux LEDs can provide illumination solutions with replacement periods of 8 to 10 years or more. This paper will examine a bridge roadway lighting feasibility study which the authors' company recently undertook. The application required the LED units to reproduce the photometric performance of 64-inch (1.625m) fluorescent lamps. In addition, the LED units were required to survive a harsh, outdoor marine environment with an expected lifetime of 7 years or more. To achieve these results, a number of design elements were studied including: optimum heat dissipation in a sealed enclosure, ease of installation, and design of power supplies having expected lifetimes to match the LED light engines. Results of these studies will be discussed as well as illustrations of the designs chosen.
Since the introduction of the Americans With Disabilities Act in 1990, the number of visual fire alarm signals installed in the United States has grown exponentially. Virtually all of these fire alarm visual signals consist of the Xenon gas flashtube type. This technology offers high intensity along with moderate cost in a relatively small package. Typical intensities offered range from 15cd (candela) up to 185cd. With the recent advances in solid state LEDs (Light Emitting Diodes) the possibility exists to develop visual fire signals using this technology. When used in lower intensity visual appliances, LEDs offer comparable light output with much smaller optical footprints (albeit at somewhat higher estimated costs). This paper will examine the optical performance of a prototype LED visual fire signaling appliance as compared to a more conventional device. It will also evaluate a series of tests, which were run in an office environment to compare the response time of workers for both the conventional Xenon fire signal appliance as well as the prototype LED device. Measurements for each test subject were taken over a two to three day period. Parameters measured included time of day, size of office and general ambient lighting. Results of these experiments indicate that the general response times of the test subjects were similar for the two types of fire signals. The paper concludes with a discussion of the potential for LED-type fire signaling devices as well as some of the potential technology obstacles still to be overcome.