White leds for backlight

Can't offer any application-specific advice, but I can tell you that I've found some REALLY bright (just received some 7500mcd green 5mm LEDs, myself) at

Hope that helps,

-Drew

Michael wrote:

You might want to look here:

It's a flashlight forum and the guys and gals there are well up to speed on high-power LEDs. They're a friendly bunch too. You might have to search around a bit, but there are links to places which sell high-power LEDs in small quantities and discussion of all the latest and greatest.

Promise yourself you won't buy a new flashlight before you go. I'm not joking. Repeat after me: I do not need 80 lumens on my keychain. I do not need 500 lumens by my bed. One brightness level is fine. My Maglite is fine. I just want info on LEDs.

Tim

The Luxeon III will produce 65 lumens at 700 mA, 80 lumens at 1000 mA. Partnumber for a white Lambertian pattern Luxeon III star is LXHL-LW3C.

Google on "Luxeon" for sources. One source

snipped-for-privacy@uton.groupSexWithoutTheY (Tim Auton) wrote in news:1hlpy4i.1tp3opy1kzipikN% snipped-for-privacy@uton.groupSexWithoutTheY:

I believe a 1W Luxeon LED has 25 lumens,a 3W ought to do better. They only use ~3.5VDC,so some sort of circuit to lower line V to that level and regulate the current is necessary.

FYI,I've seen a 3W(advertised) LuxeonLED replacement "bulb" for Maglites for sale at Wal-Mart for $20 USD. There's a different model for 2,3,or 4 cell Maglites.

I also have a 3 LED replacement assembly for my Mini-Maglite that I like much better then the standard bulb.That cost less than $5 USD.at W-M.

Wow....thanks....great info.

Luxeon looks like the winner and the prices are very reasonable....you can even order on the their site.

Like that star configuration, looks like it may not require an external heat sink (although probably a good idea anyway).

I'll have to get a variety to play with.....I may want to do 2 or 3 across rather than one 3 watt......I'm curious about how well the light diffuses......can't stand those "hot spots".

I'd just get a whole bunch of the smallest cheapest ones I could find, and see what they add up to in a dense matrix. ;-)

Although, you could get a page-sized plastic Fresnel lens - just look up "full-page magnifier" with the quotes - it'd make a nifty diffuser for one very bright one, I'd think.

Have Fun! Rich

Dollar store.

That's Future -- they'll sock you with about 9 bux shipping and a $5 handling charge for orders under $25. There are other sources with higher nominal prices that will net less for a couple of devices.

I'd use four 1-watt (45 lumen) Luxeons. You don't have to run them at wide open throttle, and I think four of them might be quite acceptable for your application. They are infinitely dimmable with no noticable color change.

It is a good idea anyway, but it doesn't take much. A 7x7 sheet of aluminum would be way plenty ample. You could even use the emitters (not stars) on a sink like that, but it's more trouble than it's worth. Then you must epoxy the emitters to the sink, and connect wires to rather fragile leads. Might be OK on a PC board with the emitters in holes in the board so the backs could be heatsunk to a plate either directly or with little aluminum posts. I've done this even with 3 watt Luxeon emitters. Works fine.

The Lambertian pattern Luxeon isn't greatly different from a bare lighbulb. It isn't quite as uniform as a bare bulb, but it spreads its radiation over most of a hemisphere with intensity about proportional to the cosine of the zenith angle. (That's why they call it Lambertian!) The "batwing" model spreads the light out even more. The more common 5mm white LEDs have much narrower beamwidths. They're very cheap in significant volume, but you'd need a lot of them to avoid hotspots over a 7x7 area and in small qty you get a lot more lumens per buck with Luxeons.

Luxeon isn't the only show in town, they're just the easiest to get in small qty. Osram and others also offer similar parts. I've never played with any but Luxeons.

Example:

Another approach migh be to mount two Lambertian Luxeons on the sides of the box near the viewing surface but aimed backwards at a bright white backdrop -- or even a textured mirror backdrop like crinkled aluminum foil or peened bright aluminum, polished stainless, etc. You'd lose a little luminous efficacy that way, but you'd probably still have lumens to spare and you certainly wouldn't have any hotspots.

Have fun!

The 3W Luxeons put out significantly more heat and will require some type of "real" heat sinking. They may also be too difficult to diffuse depending on the distance between the LEDs and the object being backlit.

I second the input to go browsing through the Candle Power forums. Lots of good information on the high-intensity LEDs there.

Ordering on the lumileds site actually redirects you to Future Electronics. So far that's where I've bought all my Luxeons and have had no complaints.

I'm experimenting with the various Luxeons for auto lights.

I think you're on the right track getting a variety of them to play with and also agree that you will do better with a couple of 1W lamps instead of a single 3W for use as a diffused light source.

Some images of how well various Luxeons diffuse can be found here (yeah - they're mine and this week I'll build an illumination target to get better objective comparisons):

Distance from LED to diffuser is about 2" - less distance diffuses less, more distance diffuses better.

The stars are very easy to work with but you may find they require additional heat sinking for long-term use depending on how well your enclosure dissipates heat. For my testing, I'm mounting them on strips of

The page-sized Fresnel won't diffuse a Luxeon - it was the first thing I tried. The Fresnel lenses used to diffuse Luxeons are scaled down to capture the rays in the range of an inch from the LED. The page-sized Fresnels are not a fine enough pattern to act as a diffuser - the LEDs retain their point source appearance.

You can get some neat projections of the LEDs themselves on your ceiling, however :-)