18 May 2008

Evolving view points for an evolving technology

To me a great majority of blog posts talking about LEDs are frankly disappointing. Although some try to take an exhaustive approach at presenting the technology in terms that can be understood by anyone, their content often remains static and academic, often copied from the same source. As these blogs are likely to come on top of the search engines responses, the casual reader may end up drawing the wrong conclusions with regards to the usability of the LEDs technology. Obviously at this point in time it would be biased to present LEDs as “the” perfect, “do-it-all” technology for general lighting. But this is a fast evolving technology, and, as for computer hardware, Moore’s law is applicable: today’s “truth” may become obsolete within a year or two. As a result, one has to remain cautious when presenting LEDs technology strengths and weaknesses.

In general lighting applications LEDs have advantages and disadvantages when compared with other light sources such as incandescent or fluorescent lamps. When looking at the positive side, the most significant advantages are fast turn-on, lower heat generation, lower power consumption, higher operating life, and high resistance to shock or vibration.

On the negative side, many blog have not been updated and retain obsolete information which may induce the casual reader into drawing hasty conclusions. Amongst the recurring limitations these blogs describe are the narrow viewing angle, and the need for electronic driver circuits to operate.

Starting by the later, LEDs need to be driven properly to ensure optimal performance and long life. An effective driver is key in obtaining all the benefits of LEDs. If early driver's implementations made of discrete components were not cost effective, this is not the case anymore. Pushed by the fast adoption of LEDs in the automotive and aeronautical industries, today almost every integrated circuit manufacturer proposes a vast array of LED drivers to suit almost every aspect of general lighting requirements. Furthermore, the leading manufacturers’ constant current sources, which until recently were only able to drive a limited number (usually 3 to 6) of power LEDs have recently been superseded by new affordable sources with 3 to 4 times more capacity.

Let’s now look at the viewing angle. First of all, light emissions from LEDs are inherently directional, thus reducing the need for reflectors and diffusers that can trap light. As a result, general lighting LEDs fixtures can potentially deliver light more efficiently to an intended location, leading to potentially higher application efficiency than other light sources in certain lighting applications. By comparison, fluorescent and incandescent lamps emit light in all directions. In their case, much of the light produced by the lamp is lost within the lighting fixture, reabsorbed by the lamp, or escapes from the fixture in a direction that is not useful for the application. For many fixture types, it is not uncommon for 40-50% of the total light to be lost before it exits the fixture.
Now, if the early generations of power LEDs were exhibiting narrow light emission angles (from 30º to 50º), the latest generations emit light at much larger angles, between 120º and 160º. This cannot be qualified as “narrow” anymore, and opens up new general lighting applications to the use of power LEDs.

Once again, as in too many cases of emerging technologies, the information for the public tends to remain far behind the actual technical advance...

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Form is the visual shape of mass and volume. Light makes form legible. There is no form without light.


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