White LED light up red??

"james" wrote in news:_8IXl.141$ snipped-for-privacy@nwrddc02.gnilink.net:

Not heard of that, specially given the right current as you have (assuming the LED's are the same model, at least nominally, as supplied). If they had damaged phosphors they'd usually look bluish, not red, so it looks like an error in parts selection somewhere. Send one back and see what response you get, could be entertaining.

Was that the exact LED you ordered? It's not possible for a white one to show up red under any circumstance, so I can only assume that you've been sent the wrong ones. ____________________ Electronic Forums -

Turns out (scroll down to see the answer)....

I reversed the polarity! I guess these are dual color LED, red and white. I thought they were only white.

"james" wrote in news:fDQXl.1753$ snipped-for-privacy@nwrddc01.gnilink.net:

I bet they're not, exactly, though they might have put a reverse biased diode of lower Vf to protect the main one against supply reversals and ESD, and it might have been easier and cheaper for them to fit the cheapest LED-type diode they could in that position rather than go for something that didn't obviously emit light. (I think all semiconductor diodes emit and respond to light to some extent anyway).

I'd guess you've been shipped the wrong part. OSRAM make good LEDS, the TOPLEDs especially so.

They have some more advanced versions now btw.

Graham

-- due to the hugely increased level of spam please make the obvious adjustment to my email address

Maybe it's fire. If you have 4V across the LED, then 50 ohms gives you

140mA. Is that how much current you wanted?

--
Jim

That's ok, for my application I don't need blinding brightness -- I want something to replace my car's dome light (0.8W) but draw a lot less current so that accidentally leaving the dome light on for days won't kill the battery.

I wish they make a version of these LEDs that is easier for hobbyists to work with. The surface mount PLCC-6 package looks impossible to solder; I'm still searching for IC socket for this...

"james" wrote in news:j%7Yl.1889$ snipped-for-privacy@nwrddc01.gnilink.net:

A brighter one can be driven less hard to get decent output so it's still worth going for a brighter one. Also, for soldering, and good heatsinking, it's worth going for something particular. A Cree X-Lamp LED is good for both counts, and is cheap enough, and there are times you'll want the brightness, so you can switch between series resistors.. RS components sell X-Lamps singly at low cost, and it might even be worth using eBay. Ideally an X-Lamp needs the right shape of pad to solder too but it's just big enough that drawing it on copper clad PCB with a Staedtler 'Lumocolor' red permanent fine tip pen will give good results for direct etching (red works better than the other colours), and you can shape the main PCB to something easily fitted wherever you want. You can even make them dimmable if you have space..

Small extra idea: use indium based solder if you can, it has a lower melting point. A bit of liquid resin flux to wet the pads, dries making them sticky, and you lay the PCB flat and stick the LED to it with the resin, then trim a small bit of indium solder and lay it beside the LED on the track, a bit for each end contact and a bigger bit for the centre heatsinking pad. I used a

65% indium/35% bismuth solder from 'scientificos' on eBay. X-Lamps like to be baked a while at around 80°C before soldering anyway, and that solder melts at only 74°C, so hot enough that it isn't going to fall off in any normal use, and cool enough to be safe to solder no matter how long you have to heat it. Capilliary action draws the metal in, so you won't get gaps under the LED. For a hotplate, just use a metal sheet on a cooker ring and a meat thermometer to gauge temperature. The same trick, with practise will let you do lots of cool stuff with very tiny parts.

I can't figure the Op's .8 W statement. No sense. Typically a 350 ma constant current drive to a Cree star would be recommended for not too much heat and better efficiency. Thats 1.4 watt. A lamp is going to be at leat 10 watts. I have just orderedsome stuff from these guys. It rediculous to no just buy a "star" unless you want some special configuration. I love the warm light I received from a Cree star I ordered from Led Supply, but this site has a lot of neat stuff. Been having some loading problems...

greg

snipped-for-privacy@zekfrivolous.com (GregS) wrote in news:h0tk9l$4sa$ snipped-for-privacy@usenet01.srv.cis.pitt.edu:

Try amps.. It probably is anyway. I have a small glass lamp like a 1.25" fuse with a 12V filament in it, which draws 0.3mA or so. If most modern inside lamps for cars use the fatter glass envelope with the conical extensions on the end caps, they can probably draw 0.8A and be rated for 8 or 10 watts instead of 4 or 5 which the fuse-like ones are.

Exactly, nice low current to match many standard car lamps, and nice colour rendering too, although to save energy and match output, lower current is right, but I don't know how much.. I know X-Lamps still make nice light at lower currents. Not bought a star before though, I always thought they'd be a lot more expensive than the X-Lamp. But if the difference is worth it for easy mounting and heatsinking, then sure.. I had a specific design that warranted all the effort I described in another post, but for a one off in adequate space I'd reconsider.

I bought 3 of these. I burnt out 2 cause my supply caused a slight peak overcurrent for some reason. They don't seem a rugged as the Luxeons, but I would recommend them. I installed one in the bathroom at 50 ma. drive its bright for an under cabnet light/night light. I love the color.

greg