Overview of Outdoor Area Lighting

Lighting of outdoor areas including streets, roadways, parking lots, and pedestrian areas is currently dominated by metal halide (MH) and high-pressure sodium (HPS) sources. These relatively energy-efficient light sources have been in use for many years and have well-understood performance characteristics. Recent advances in LED technology have resulted in a new option for outdoor area lighting, with several potential advantages over MH and HPS sources. Well-designed LED outdoor luminaires can provide the required surface illuminance using less energy and with improved uniformity, compared to HID sources. LED luminaires may also have significantly longer life (50,000 hours or more, compared to 15,000 to 35,000 hours) with better lumen maintenance. Other LED advantages include: they contain no mercury, lead, or other known disposal hazards; and they come on instantly without run-up time or restrike delay. Further, while MH and HPS technologies continue to improve incrementally, LED technology is improving very rapidly in terms of luminous efficacy, color quality, optical design, thermal management, and cost.

Current LED product quality can vary significantly among manufacturers, so due diligence is required in their proper selection and use. LED performance is highly sensitive to thermal and electrical design weaknesses that can lead to rapid lumen depreciation or premature failure. Further, long-term performance data do not exist given the early stage of the technology’s development. Interested users should continue to monitor available information sources on product performance and lifetime, such as CALiPER test results and GATEWAY demonstration program reports.

Design and Specification Considerations

Many issues enter into design and specification decisions for outdoor lighting. Energy efficiency is especially a priority in this application due to the long running hours and relatively high wattages typically involved. This section looks in detail at energy efficiency factors, as well as issues related to durability, color quality, life and lumen maintenance, light distribution and glare, and cost.

Figure 1. Several HPS fixtures (left) were replaced with LED pole-top mounted luminaires (right) to illuminate a pedestrian area at a Federal Aviation Administration facility in Atlantic City, NJ. A full report on this installation is available.