Finding specifications

I've been toying with the idea of getting a whole lot of bright yellow LEDs, and setting them up in a strip mounted under the front bumper of my car to use as fog lights. They are low power, don't put out a lot of heat and are a lot less susceptible to catastrophic failure from a rock than are glass lens halogens.

The problem that I'm having is finding out how many LEDs it would take to equal the light output of a conventional foglight. I can find specs for LEDs, but not for the halogens.

To make sure that I'm comparing apples and oranges, I assume that there are two measuremnets, light output (photos per second) and intensity (photons per second per square cm).

It being over 20 years since my last physics class, I don't remember what all the various units are.

Can someone point me to a good description of what the various units of measurement, and also, to some actual specifications, or ideally comparisons for the various lights?

[highlandsun]

All the relevant specs you could ever hope for are at the Philips Lighting web site:

http://www.lighting.philips.com/nam/.../mini_seal.pdf

It will take around 300-500 5mm LEDs to equal one 27W incandescent bulb. See my web site for more links and info:

http://home.attbi.com/~hyc_sub1/signal/

Your best bet is to use a number of 1W amber Luxeon Stars, as I did. A 55W H3 bulb (typically used in fog lights) produces 1050 lumens. Each amber Luxeon driven at normal specs produces 36 lumens. Assuming that you were replacing a tinted fog light, let's say that the 1050 lumens is reduced 20% by the tint, so you're shooting for around 800 lumens for a single fog lamp, 1600 lumens total. That would take about 44 Luxeon Stars. Still quite a lot, lots of soldering and mounting issues...

I've considered doing this myself, just haven't gotten motivated enough yet. 44W in LEDs vs 110W in two H3 bulbs, I dunno. About 2000 5mm LEDs if you go that route. Very expensive, no matter what.

If I were doing this, I would use 8 parallel strings of 6 Luxeons in series. The Vf for each string would then be right around 14.4V, which is what the car's electrical system delivers when the engine and alternator is running. They would be noticably dimmer with the engine off, but would still provide a good amount of light.

Thanks a bunch, this was exactly the information I was looking for. I was guessing that it would take 50-100 LEDs, I guess we aren't quite there yet.

[highlandsun]

Definitely, there's a ways to go still. I think the auto manufacturers using 5W white Luxeons for headlights have their heads up their asses. LEDs aren't ready to displace halogen or HID main lighting yet. For signal lighting, yes. Primary illumination, no...