BulbCollector Forums
BULB DISCUSSION BOARDS => Christmas Lighting => Topic started by: Derek R on October 31, 2003, 08:10:00 am
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Hi folks! This is more of a Halloween query rather than Christmas which makes it a) probably in the wrong forum, but b) topical.
I was working in the lab late one night waiting for a laser tube to warm up so had an hour or so to spare. I started messing around with a bog-standard 5mm diam green LED (25mA max, about 5mcd at 10mA, running at about 2.5V)and happened to dunk it into a dewer of liquid nitrogen. With all the other lighting off this looked quite spooky as clouds of gas and vapour were being boiled off,reflecting the light as they billowed about. I got to wondering just how dramatic this could become so upped the current limit on the bench supply (the LED had no series resistor fitted). The max available was 3A, but the ambient temp at the business end was -77deg C (equiv to -106degF or 196K).
This was bright enough to illuminate the faces huddled over the turbulant cauldron chanting "when shall we three meet again?"
Of course the interesting part was when the connecting wires were pulled to remove the LED from the N2. It actually lasted about a second before expiring with narry a whimper let alone a satisfying bang.
So... what is the brightest a "standard" LED of this size can acheive? What is the max current attainable? Is there any commercial use for very bright, very cold, high current, illumination devices?
(I'm assuming liquid helium is beyond the scope of most us)
Of course, if you've nothing better to do this evening...
Happy Halloween.
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Oops! Brain is not quite working.
You will have noticed that liquid N2 is at -196degC, 77K or -320degF. The numbers look about the same, hence my complete confusion.
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Hi Derek,
The LN2 trick makes an excellent demo of how sensitive LEDs really are to temperature! Try it with an AlInGaP red LED and you'll be amazed how bright it goes.
The brightest LED on the market at the present time is a 700mA device from Philips. In the white version (blue chip + yellow phosphor) it produces about 120 lumens and draws 5 watts. Thats producing the same amount of light as a 10W halogen bulb. Check out www.luxeon.com (http://www.luxeon.com) for the specs if you're interested.
James