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David, Surrey UK
08-29-2007 13:13:00
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Re: LED Trailer Lights in reply to JPatton, 08-24-2007 19:52:28
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I don't know much about trailer lights, but coming from an electronics background I can tell you a bit about the LED devices themselves.
There are a number of variables. First, the efficacy (lumens per watt) can vary; some devices are inherently brighter than others. This depends on how they're made.
Second, the emission angle varies. Incandescent bulbs emit light in all directions, but LEDs tend to beam it out in a narrow beam. The narrower the beam, the brighter the light appears, but if you go off beam the light intensity dies away quickly. In practice you want a reasonably wide beam so you can be seen from all angles. The LED itself is encased in a plastic lens, and sometimes these are clear, other times translucent. The translucent ones spread the light over a wider angle but this makes them look dimmer.
Third, in a practical application like trailer lights, the LED device will probably be behind some sort of protective plastic optics, which will further affect the way the light behaves.
Fourth, the amount of light put out depends on the current passing through the LEDs. But since the eye has a logarithmic response, doubling the current won't double the apparent brightness. Too much current and the LEDs will have a short life.
Fifth, a single LED is almost a point source, but to be visible from a distance you want a large illuminated area, hence lots of LEDs are needed.
I don't suppose that's very helpful, but it's background info! 
Even more about LEDs here: Link
David
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