Led light new

[steve]

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.

 

[Rich Webb]

On Thu, 30 Dec 2010 06:41:31 -0800 (PST), steve <kvsteve@gmail.com>
wrote:

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.

The magic smoke probably got away.

Anyone know of good led specs, please provide.

Read the topic over at http://www.cappels.org/dproj/ledpage/leddrv.htm
It's geared to the experimenter and should give you some ideas about
where to go with this.

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

 

[Michael Black]

On Thu, 30 Dec 2010, steve wrote:

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.

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

 

[Rich Webb]

On Thu, 30 Dec 2010 11:42:24 -0500, Michael Black <et472@ncf.ca> wrote:

The only reason for making your own LED flashlight at this point is to
put it into a custom enclosure or situation.

Well, that and curiosity / learning / "play."

--
Rich Webb Norfolk, VA

 

On Thu, 30 Dec 2010 13:30:57 -0500, Rich Webb
<bbew.ar@mapson.nozirev.ten> wrote:

On Thu, 30 Dec 2010 11:42:24 -0500, Michael Black <et472@ncf.ca> wrote:

The only reason for making your own LED flashlight at this point is to
put it into a custom enclosure or situation.

Well, that and curiosity / learning / "play."

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).