Light-emitting diode (LED) luminaires are ready to take their place at the apex of exterior lighting, even though our realization of their full potential is still a long way off. The power of these units has increased, making them capable of replacing 1,000-watt HID bulbs like high pressure sodium and metal halide. They do this with much greater uniformity of light distribution. They use a fraction of the energy required for most competing light sources and can last up to 20 years.

Many are now manufactured with plate-mounted LEDs that can be swapped to change power output and lighting pattern. This means that individual components can now be replaced or upgraded without removing the entire fixture. There are a few worthy competitors, like induction lighting, and LED lighting is not the best choice for all applications. That said, they are emerging as a real winner.

Heat Can Shorten Life Span
Now that their praises have been sung, it’s important to know a little more about their operation. These tiny light emitters are a little different. The biggest problem with LEDs is heat.

With incandescent light bulbs, only 20% of the energy output becomes light; the rest is radiated away from the bulb as heat. LEDs cannot radiate heat, so it builds up inside and shortens bulb life, unless the heat can effectively be siphoned off. 

Heat must be conducted away from LED bulbs through the base and radiated away through efficiently designed heat sinks. Heat dissipation is often handled in the unit case. The fins incorporated into case design are there to increase surface area for efficient heat exchange. The efficiency of the heat dissipation process is a major key to the quality and life expectancy of these units. This also means that LED life expectancy will be lower in hot climates.

LEDs Require Upkeep
The term “life expectancy” is a little different with LEDs than with conventional bulbs.  Most regular bulbs maintain their light output until the moment of their demise, which occurs suddenly. The life expectancy of these bulbs is the calculated number of hours where 50% of the bulbs are expected to fail.

LEDs do not fail suddenly; they just continue to produce less light. Like the old soldier, LEDs never die, they just fade away. LED life expectancy is calculated at the point where 30% of their light output has been lost. This level of loss was selected because the human eye is incapable of perceiving a 30% drop in light output.

There is good news and bad news with this gradual failure syndrome. The good news is that LEDs don’t just die under normal circumstances, a trait that can leave dangerous dark areas without coverage until someone reports them or they are detected in a good maintenance program. Remember that most personnel charged with light maintenance work when the sun is up.

The bad news is that the human eye cannot be relied on to measure the point at which the bulbs should be replaced. This means that the measurement of light output with a quality illuminance meter must be incorporated into the maintenance program.

Dissipate Heat to Extend Life
Knowing how LEDs die makes it easier to understand how their life can be extended.  As mentioned, heat is the greatest factor in determining life expectancy. Hot climates shorten life, efficient heat dissipation extends life. Operating the lights at less than full capacity also extends bulb life.

This leads to another area of potential cost savings. Light controllers can be used to lower light output during off-peak hours. A 50% reduction in light output can increase the life of an LED from 60,000 hours to 160,000 hours. Controllers can also be programmed to reduce light output during periods of high temperature. They can even turn off every other light fixture in a string. Wireless light fixtures are now available that can do all of these things without having to dig trenches for the control wiring circuits. Controllers can also be used to raise all light levels to maximum during an emergency, which can be a powerful crime deterrent.

LED lighting systems when combined with a quality light controller offer a great combination for reducing light cost while increasing system versatility. They have reached the point where their cost and benefit make them a hard act to beat.

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The Evolution of LEDs

It all began when photons started popping unexpectedly out of someone’s diode. Diodes are those little lumps of glass that form the backbone of all modern electronics from transistors to microchips. The phenomenon, called electroluminescence, was discovered in Great Britain way back in 1908. It took another 60 years before the price dropped enough for lighting applications to develop.

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