On Wed, 15 Oct 2003 14:52:10 -0500, Bob Robinson
wrote:

AL A. wrote:
Hi all,
I know this is not strictly on topic, but this crew seems to know something
about everythig, so here goes:

I am looking to build a "task" lamp (think dentist-type light) that uses
high output white LEDs for a friend who often does
work for extended periods of time in very remote places. I was looking at
the NTE electronics "lightwave" flashlights
http://www.nteinc.com/lightwave/ and they claim that they have circuitry
that makes it possible to run one of the 10
led lights for 24 days, continuously, on 3 D cells.

Any idea how they accomplish that? Most of the high output LEDs I have seen
seem to want to run between 20 and 40 mA
current draw. Given the amp-hour ratings I find for D cells, I don't see how
that would work out. Do they modulate the power to the LEDs
in some way that helps extend the battery life so dramatically?

I looked at just modifing a lightwave flashlight for the task at hand, but
the beam is a bit too wide for what he needs. So I am hoping to
build something with maybe 3 LEDs and appropriate optics to give a fairly
narrow, even beam, mounted on a gooseneck type thing,
with a remote battery pack on a cord.

Any thoughts on the electronics involved? I can handle that part of it, if
I know what I am trying to accomplish.Of course the body
of the thing will be METAL, nicely turned, naturally. (obligatory
metalworking content...)

Thanks for any ideas you can offer.
-AL


AL,

I'm working on a similar project at the moment. Here's what my research
has yielded so far. The majority of ultra bright leds do operate in the
20-40ma range, and the forward voltage is around 1.5-1.7V. If you
arrange the 3 LEDs in series with at least enough cells to provide 4.5V
and an appropriate current-limiting resistor, your current draw will be
20-40ma. If the NTE light is using 7 LEDs with 3 D cells, they are
wiring them in parallel, so the current draw is at least 140ma and the
24 hr figure is highly suspect. If you connect yours in parallel, you
could get by with 2 1.5V cells, but your current draw would triple.

Hope this helps,

Bob

If you folks come up with decent LED flashlights, or plans..the people
over on misc.survivalism would love to have some, as this is a regular
topic of discussion.

Gunner

"You cannot invade the mainland United States. There would be a rifle
behind each blade of grass." --Japanese Admiral Isoroku Yamamoto