Since the 1990s cities in the US and Europe began replacing incandescent-based traffic lights with higher energy-efficient solid state lights, LED has been taking to streets. At that time LED is not powerful enough to be used in street lighting. In the past period, the technology of LED progressed. Now more and more street lighting projects choose LED sources. It took the market of high pressure sodium and mercury vapor gradually.
Why LED?
1) High Energy Efficiency. Today the power efficiency of LED is over 100lm / w. In most of street lighting project, the power efficiency of LED is 65-80lm / w. It's much higher than 30lm / w from mercury vapor lamps.
2) Eco-friendly. LED lighting is solid state lighting.
3) Long Lifetime. The lifetime of LED is 50,000 – 100,000 hours.
Philips used its LUXEON Rebel LED to test. LUXEON Rebel LED stacks up against the two dominant lighting technologies High Pressure Sodium and Mercury Vapor used for street lighting. The results are as follow:
LUXEON Rebel High Pressure Sodium Mercury Vapor
Flux (lm) 3325 5510 4340
Power consumption 67W 90W 138W
System Efficacy (lm / W) 50 61 31
Average Lux 14 19 14
Utilization 0.0042 0.0034 0.0032
Lux / W 0.21 0.21 0.10
Min / avg Lux Ratio 0.40 0.32 0.23
Lifetime (hours) 60,000 20,000- 30,000 6,000 – 10,000
From the above data, we can find the following results.
1). Low power consumption – LED street lights (67W) save energy use by 52% over Mercury Vapor lamps (138W) and 26% over a high pressure sodium lamps (90W)
2). Higher power efficiency – LED street lights exceeded mercury vapor's 31 lm / W. You can find higher efficiency measurement from for high pressure sodium lamps. It is just misleading because it includes wasted light that in turn wastes energy. In the market, many power efficiency of LED street lights can reach up to 80lm / w.
3). More Lux Per Watt – more than double that of a mercury vapor street light. The equivalent measure for high pressure sodium lamps is skewed by hot spots that bump up the lux rating but cause undesirable visibility, safety and glare problems.
4) More even light distribution (0.40) than both High Pressure Sodium and Mercury Vapor. The LED scenario was the only one of the three to match the European street lighting guidelines on this uniformity measure. because of its ability to intentionally direct light.
5) Longer lifetime (60,000 hours) – Lifetime of LED can be translated into a 10 to 15 year life expectancy.
