Since on the topic of Led light, I heve been trying to make a diy pocket torch, but the latest available (white) Led will not work below
3v.With 9v dc, it flashed briefly and stopped.
Anyone know of good led specs, please provide.
Thanks.
Steve.
The magic smoke probably got away.
Read the topic over at
Briefly, LEDs have a (very) roughly constant forward voltage drop, around 2 V for red/yellow/green LEDs and 3.5 to 4.5 for blue and white. They also have specs for normal and min/max operating currents, usually in the range of 5 to 20 mA.
With your 9 V battery and assuming a 4 V forward voltage drop, for a usually safe 10 mA through the LED you would want a resistor that's about (9 - 4) / .01, or 500 ohms in series with the LED. A 470 ohm is a common standard value and would probably work okay.
Without that, your current through the LED is limited only by the internal resistance of the battery and the LED itself. Thus the brief flash (the equivalent of an LED screaming).
LEDs are really happier with a constant current source, which can be approximated by the battery + resistor. It's not a terribly efficient method (more power would be used in the resistor here than the LED) but it's the simplest.
-- Rich Webb Norfolk, VA
Go back and read the archives of this newsgroup at google.
About a decade ago, maybe not even that long, various people were posting about their work on making their own LED flashlights. Often, they used upconverters to get the needed voltage, from AAA or AA batteries that had better current capacity than 9v batteries. They went through various iterations.
Note that nobody talks about making their own LED flashlights anymore. At the time, the LEDs were available, but still expensive, and LED flashlights were even more expensive. Then the prices started falling. About December of 2004 or 2005, I bought an LED bike light because it was cheaper than most LED flashlights at the time, and I wondered if it was any worse. It wasn't. But another wave came along, I replaced the lightbulb in my 2AA maglite with an LED adapter kit.
Now, I have them all over the place, each time they add more LEDs the price is the same as the last time I bought an LED flashlight (with fewer LEDs). My LED flashlight with the hand crank has already expired, the battery needs replacing. Meanwhile, for Christmas, I was given a tiny and cheap solar powered LED flashlight.
The only reason for making your own LED flashlight at this point is to put it into a custom enclosure or situation. And even then, one comes out ahead starting with a cheap LED flashlight and repackaging it. Gee, I wanted to replace some tiny bulbs in a shortwave radio, and I'm better off buying a cheap LED flashlight and extracting the LEDs from that for the purpose.
Michael
Well, that and curiosity / learning / "play."
-- Rich Webb Norfolk, VA
Roger that.
Leds still seem like miracle devices to those of us who grew up with incandescent's for ALL lighting. I can't wait to get my hands on the "latest and greatest" Leds then find a place for them.
A lot like that first transistor amp - here was a stereo amplifier with no toobs - and it worked!
Led flashlight ... ~1992 (first kid on my block to have one).
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