Perhaps even more of an advantage than the considerable energy saving capabilities of these astonishing little marvels is their incredibly long life. The lifespan of a LED is vastly longer than that of incandescent, fluorescent or HID lamp sources: a high quality LED will generally last 70,000 hours or longer. A LED does not burn out like a standard lamp, so individual diodes do not need to be replaced on an array. Instead, the diodes gradually produce lower output levels over a very long period of time. If one LED fails, it does not produce a complete fixture outage.
Although LEDs never really burn out, product lifespan is measured by lumen depreciation. The Illuminating Engineering Society (IES) currently recommends calculating the life of an LED as the point at which the LED reaches 30 percent lumen depreciation.
It's important to remember that an LED's 70,000-hour rating is not equivalent to a 70,000-hour lamp life rating (if such a thing existed). A high quality LED will function for well over 100,000 hours in its capacity as a light emitting diode. An LED's functional life is rated up to a point where the LED has reached 30% lumen depreciation. In other words, a high-end LED rated at 100,000+ hours would be used as a light source for approximately 70,000 hours. After 70,000 hours, the LED would still be operational, but at a decreased lumen output and would warrant replacement as per IES standards.
Deconstructed it comes out to this:
If a LED fixture is illuminated an average of 8 hours per day it will last over 20 years before needing to be replaced.
That sentence has tremendous implications for cities, project managers, project owners and the environment.
A high-pressure sodium luminaire needs to be relamped every 20,000 - 24,000 hours and a metal halide luminaire every 10,000 - 16,000 hours. Over time, LED life will increase beyond 20 years thanks to all the material research currently being undertaken, causing LED luminaires to get considerable upgrades every time they reach the end of their light source's lifespan, increasing the value and efficiency of the luminaire over time. It is speculation, but it makes sense to postulate that over the next 20 years, LED life will continue to increase, as it has been for the previous ten. It is not speculation to say HID technology has reached its peek. Not only do LED luminaires last 3 - 7 times longer than HID luminaires before needing their LEDs replaced, but with each replacement they benefit from improved versions of themselves that last even longer and consume even less energy. Sustainable technological evolution at its finest.
Imagine two identical cities, one lit exclusively by high-end LED luminaires and one with traditional HID luminaires. The obvious benefit to the LED lit city would be the 30% power consumption reduction from the use of high-end LED lighting. That benefit engenders many positive transformations for that city from lower energy bills to lower taxes and higher property values.
Imagine that both these cities have 30,000 luminaires spread throughout. For the LED city there are other, less obvious yet just as spectacular, benefits to be had from the longer lifespan of LEDs.
A HID luminaire needs a minimum of 3 relamps during the 30% lumen depreciation lifespan of the LEDs in a LED luminaire. 30,000 different locations to where a truck has to drive to and from, a minimum of 3, and up to 6 times for HID luminaires. Just for light source replacements it takes 90,000-180,000 fleet deployments over 20 years to every spot in the HID city but only 30,000 trips in the LED city.
Besides reducing their lighting power consumption by 30%, the other benefits for the LED city also begin to come into play:
Gas consumption for fleet decreased
Man power allocated to HID luminaire maintenance reassigned
Major reduction in city carbon foot print
Major reduction on fleet maintenance costs
Major reduction in smog
Increase in city population
Increase in city maintenance and city enhancement results
Beautification of city
Considerable city growth as a result of reduced maintenance requirements and fleet travel
This is a fact: in 2008, high-end LED photometric performance rivals, and sometimes even shames, that of HID luminaires.
LED luminaires are here. They are ready. This is no longer a theoretical scenario. There are so many subtle yet powerful benefits that combined, create a domino effect that can change any environment for the better.