The nature of white LED lighting

idleprocess · #1 10-03-2004, 05:08 PM

IS it just me, or is the light from a white LED just prone to more attenuation than the more yellow light from a typical incadescent bulb?

There was a blackout while I was at a friend's house in a semi-rural area last night, and it seemed that the beam from my 3W LED light (VIP) just sort of petered out past 100-150 feet or so with the ~25mm reflector installed.

There's also some backscatter from the beam - possibly due to the humid climate here in DFW, pollution, and dust in the air from the gravel roads around.

Of course, 3W isn't a great deal of power to throw a long ways compared to some of the hotwire and HID monsters others are playing with.

jtr1962 · #2 10-03-2004, 06:12 PM

It's true that yellow light carries further under fog conditions. Pollution and dust are somewhat similar to fog in the way they scatter light. Of course, you need to compare apples to apples here. LEDs can't be as strongly focused as incandescents, at least not yet, so of course the hot spot in an incandescent will carry further. On the other hand, the whiter LED light does provide greater constrast which partially makes up for the increased scatter. Overall, I would probably say that except under very foggy conditions yellow incandescent light will give no advantage over LED light, all other things being equal of course.

idleprocess · #3 10-03-2004, 06:29 PM

The average incadescent flashlight filament seems to have greater difficulty focusing than the flat surface of a Luxeon emitter, which is closer to a point source than all but the shortest of incadescent filaments that often occupy space long the Z-axis, posing greater challenges to proper fousing.

I could be wrong, but parabolic reflectors are optomized for point sources...

jtr1962 · #4 10-03-2004, 07:27 PM

A true parabolic reflector is optimized for a point source, and would probably work better with an LED than with most incandescents. Many flashlights these days have computer-designed reflectors optimized for a particular type of bulb and filament. These seem pretty close to parabolic along the filament axis, but not perpendicular to it. If I'm not mistaken a true parabolic reflector would give a magnified image of the filament (unless it was very small), rather than a hot spot like a computer optimized reflector.

idleprocess · #5 10-03-2004, 09:16 PM

As a resident of the Dallas area, I can say that it is fairly humid here, and the pollution level is somewhat high for most urban areas in the US.

Maybe I just need a larger reflector...

kakster · #6 10-03-2004, 09:34 PM

Even an overdriven LuxeonV in a 2.5" reflector will get washed out if there is any ambient light. This subject has been brought up before, a few ideas were kicked around, but no-one had a definitive answer. The most likely theory IMHO is the lack of full spectrum light from LEDs.

Lumen for lumen, an incan lightsource will be more useful at a distance than even the most tightly focussed LED (unless we're talking pitch black conditions). Maybe once the warm white range gets up to speed, things will even out a bit.