While some companies are pushing the outer limits of appropriate LED general lighting applications (think LEDs in a T8 form factor), others are focused on the ready-for-prime-time applications such as street and area lighting. Municipalities and companies with the ability to cover the upfront costs can find much to like about converting from HID to LED.
The whiter appearance of LEDs should produce safer visual conditions. Humans are more visually alert in white light environments than in the pronounced “yellow” light of high pressure sodium, a common light source for street and area lighting installations.
Properly designed LED systems should be able to meet the industry standard illumination levels and uniformity while using less power. However, the lumen depreciation of the LED system might lessen the power benefit over time. For example, if over the course of the 50,000 to 100,000 expected life of the LEDs, the light output declines 30% from the initial (not an unreasonable assumption with LEDs), then the system could fall below industry standard illumination levels before end-of-life for the LEDs.
Theoretically the life of the LED system (50,000 to 100,000 hours) looks like a significant benefit compared to the 25,000 hour life of high pressure sodium lamps. LED proponents often tout reduced frequency of re-lamping as a major factor in evaluating cost-effectiveness. Indeed, re-lamping street lights is not a trivial task and if the number of re-lampings can be cut in half, the financial impact is real and quantifiable. However, because there is little long term history with LED systems, other maintenance issues unique to LEDs may emerge.
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute in New York has done extensive research on LEDs and LED system applications. Follow this link for a detailed case study on LED street lighting. While you are on their web site, check out the other interesting lighting research going on at the LRC.
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