For those techies that want to make their own white LED flashlights:

Hosfelt Electronics (no web site) at 1-800-524-6464 has the Nichia bright white LEDs as part # 25-353 for $3.99 each. Connect 3 in series with no series resistor directly to a 12V lead-acid battery for maximum efficiency, or 2 plus a 25 mA current limiter for best brightness control. I found that 2 were as bright as a good bright penlight, and hat even 1 was good enough to read by. Cold white light, slightly bluish, since these LEDs are actually blue with a white phosphoroverlay.

An earlier thread on this is at:

previous thread

-- Anonymous99 (Anonymous99@anonymous.com), February 16, 1999

Answers

I called and ordered 10 to play with.

Specs I was quoted: 3.6-4.0 volts operating range, 20mA current usage, and 2000 mcd luminosity. 2000 seems kinda mild. The Rat Shack so called orange are 12,000. Best luck I've had so far is one rat shack 12K orange (red) and one 6K Rat Shack yellow. Makes a usable light that you can reasonably read with, runs easily on 2 AA's, and all fits in a 1x2x4 project box.

First build used one 12,000 mcd Orange (red). It was suitable to find your way around in a dark room and you could read if you HAD to. Good news is I left it on for 212 hours stright. Didn't kill batteries, just got tired of waiting and wanted to tear it down and play. That's when I took out the pot I had soldered in and replaced it with 50ohm resisters going to TWO LEDS, one red and one yellow. Much better light. Replaced batteries and turned it on Saturday at 11am. Still going strong as of Tue 7am. I expect at least a week solid use.

The yellow is half the brightness of the red, but is a much better spectrum to read by or see with.

I'll play with the whites (blues) to see what I can do with them. Next project after I get this worked out to my satisfaction is a LED stand light to light my HAM work station, then a IR light to suplement my night vision.

-- Art Welling (artw@lancnews.infi.net), February 16, 1999.

If you want to have fingertip brightness control and the ability to REALLY stretch the battery life, especially when using multiple LEDs in a circuit, build a PWM driver.

It's a simple circuit using a CMOS 555 timer chip (Make sure to get the CMOS version of the 555 as it draws a LOT less current to run...) to drive a power FET (IRF511 or similar with a small heatsink) which in turn pulses current through the LED(s). If properly built with a fast enough frequency (+50 KHz) and low enough duty cycle (10-30%) you can drive an LED array with much more power than its maximum without torching the LEDs.

I used a similar circuit to drop ten-amp pulses through a laser diode that was rated to draw about 100 mA max. Kept the duty cycle really short and got into the tens of watts from a half-watt IR laser diode. (Side note: The IR was detectable for several miles! It was pretty much line-of-sight detection range.)

In fact, with such a goodie to drive it, you could probably build your own pseudo-white light using one of those Radio Slack 12,000 mcd orange LEDs, a couple of their brightest green LEDs, and another couple of their blue LEDs. (Better yet, find a few decent colors and brightnesses by experimentation or buy a fistful of those white LEDs if you can.)

A driver circuit for this can be found in that little 555 experimenter's handbook Radio Slack sells for a couple bucks. Should cost less than $10 for the parts and if you use a pot to vary the duty cycle/rate you can dial-a-brightness. The whole circuit can be built as small as two square inches if you're decent at dense- population circuit design and can solder well in tight spots.

OddOne, who's built many a thing with a 555 chip...

-- OddOne (mocklamer@geocities.com), February 16, 1999.

There are two parts to an LED brightness specification: the brightness (in mcd) and the angle of illumination (angle of the cone in front of the device that gets illuminated).

For example, a fraction of a dollar gets you an HP amber ultrabright LED, and you can choose from

9300mcd into 6 degrees 3100mcd into 15 degrees 1800mcd into 23 degrees 1300mcd into 30 degrees

Which sort you want depends on what you want to do: a spotlight or an area light? In efficiency terms, the last puts out the most light, but in a less concentrated way.

Beware of this if you buy purely on mcd rating; it may be a rather small patch that gets lit!

White LEDs are somewhat less efficient than amber ones, and also cost about 10x as much. It's an easier light to work with, though.

-- Nigel Arnot (nra@maxwell.ph.kcl.ac.uk), February 17, 1999.

Anyone willing to give a parts list and some specific assembly instructions?

Close is okay if you know what to do and what to expect but bunches of us don't have that background knowledge.

Thanks.

-- j (sandpine@juno.com), February 17, 1999.

There are a few more specifics at:

previous thread

Look for my post near the bottom starting off something like:

"For the non-soldering-iron-impaired..."

While it does not have specific instructions, it tells you where to find them...

-- Anonymous99 (Anonymous99@anonymous.com), February 17, 1999.

"Beware of this if you buy purely on mcd rating; it may be a rather small patch that gets lit!

Absolutely! The 12,000 MCD oranges I got from Radio Shaft are rather narrowly focused. Good for small flashlight in the 5-15 foot range. Rather narrow for reading, unless you suspend the light about 3 feet from the reading material.

-- Anonymous99 (Anonymous99@anonymous.com), February 17, 1999.