The latest buzz in energy efficient lighting has been focused on LEDs, or light emitting diodes. LEDs are being touted as the next big thing in the lighting industry.

There are many advantages associated with LEDs .They are solid state lighting (SSL.)  An LED produces light energy as a byproduct of passing an electrical current through semi-conducting material. Because they use a solid- rather than gas-based process and rarely contain any glass, LEDs are significantly more durable than traditional lamps. There are no filaments or other similar “loose” parts, so they are also resistant to vibration. 

With all of these advantages, the question remains why aren’t LEDs more readily available for general lighting applications?

There are some technology issues to be worked out.  One has to do with the quality of light produced and the other addresses the removal of waste heat. LEDs also have an input power limit. For high power applications, LEDs efficacy is indistinguishable from CFLs (compact florescent lamps).

The big advantage of inefficient, heat-producing incandescent lamps is that they emit light that is most similar to natural light.  This is important because it affects the way that we perceive color. The quality of light is evaluated based on its color rendering index (CRI), which describes how well the light renders color on a scale of 0 to 100, and its correlated color temperature (CCT), which describes the apparent color of a white light source.  A standard incandescent lamp has a CRI of 100 and a CCT of 2700 Kelvin (K), indicating that its light appears yellow/gold, similar to sunlight.  Energy efficient CFLs have a CRI of at least 80 and a CCT of 2700-3000 K.

Unlike traditional light sources, LEDs do not emit white light, so their light must be converted for use in general lighting applications.  This inherent difference makes it difficult to judge the color rendering capacity of LED lights because CRI scores do not accurately depict their color rendering quality.  In addition, LEDs are most energy efficient with high CCTs, producing a bluish rather than yellow/gold light.  LEDs with the same CCT range as CFLs are often less energy efficient.  The goal is to provide a high-quality light source with comparable or better energy efficiency.

The other is effectively dealing with waste heat.  Unlike other light sources that radiate heat, LEDs conduct heat, although minimal in comparison, it can significantly reduce longevity if not removed from the device.  Effectively moving the heat away from the device becomes an issue in applications where space is at a premium, which describes many lighting applications traditionally served by incandescent lamps.

Recent developments in LED technology, however, have been addressing these issues.

Eng.Benard Makaa,PE

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