I just purchased a Coleman 5310 lantern. It is a small lantern using 4 D cells with a flashlight type bulb. It has a dimmer that doesn't reduce the voltage. It appears perfect to convert to using leds. Help ! What resistors, leds, should I use. It puts our a little over 6 volts. Thanks !

-- reed moore (reed_moore@postmaster.co.uk), June 07, 1999

Answers

I don't have the formula handy, but I suggest that you trek down to your local Trash Shack (Radio Shack). The one think Trash Shack does that I like is sell lots of electronics components that you usually don't find in shopping-mall retail outlets.

Trash Shack sells the orange & yellow LEDs, but more importantly, has an "Engineer's Notebook", and lots of other similar "books" with lots of formulas and projects for doing this sort of thing. These "books" are only about 10-30 pages, made from very cheap paper, but cost very little, and "just what the doctor ordered"...

-- Anonymous99 (Anonymous99@Anonymous99.xxx), June 07, 1999.

Cory made a recent comment about led lights on an ongoing thread at csy2k. His idea of a set up with a few snakelight type flashlights is a good one.

Our led flash light sends the beam straight out, I'm not sure the Coleman lamp wouldn't waste alot of your light in the wrong direction.

The solar outdoor lamps have special prisms to distribute the beam.

-- flora (***@__._), June 07, 1999.

REED:

Your local Trash Shack DOES sell LEDs, but their "mcd" ratings are way too low, & their prices way too high.

Want to find out what mcd means & how to build your own? Two sources: Cory Hamasaki's project uses medium output white LEDs with high power drain. My design uses very high output (18,000 mcd) yellow LEDs with low power drain (20 mils.) (I wrote svl articles on them a year ago -- do a search for them with 'Schenker' and 'LED'in the archives of http//y2k.entrewave.com Tells you how to build them from scratch with sources for reasonably-priced LEDs, in single quantities. The design has got some weaknesses, but they work fine. Could use somebody else's input -- like a design engineer's ( :]= ).

Bill

-- William J. Schenker, MD (wjs@linkfast.net), June 07, 1999.

>>My design >> uses very high output (18,000 mcd) yellow LEDs with low power >> drain (20 mils.) (I

Doc,

I played with several kinds, including infrared for night vision use. It's true that some colored ones are rated at higher luminosity output, but they are not as 'bright'. Let me explain.

I found that a 6000MCD yellow was way 'brighter' than a 12000MCD orange LED. Well.... WHY??? Then I studied a bit and it seems that LED's are very tight spectrum light emitters. If the light frequency is not as efficient for the human eye then the higher output is wasted.

Personally, I have found that a 2000MCD blue/white LED is about 10 times more useful than a 12000MCD orange. I arrayed (4) 2000MCD blue/whites in a project box and drove them from a 9v battery through a 50 ohm resister. I used momentary contact buttons so they would not be left on. Can't tell you how long they last, I built two of them 3-4 months ago and they are still on the same batteries despite my letting the kids play with them as much as they want.

These shirt pocket lights are blinding if you look directly at the LED emitters. They provide enough light to walk around a room, find your way in the dark, and read COMFORTABLY at 12-14 inches. I use mine in our camper, going for stove wood, checking my chickens and gathering eggs, and by my bedside to tune the shortwave.

Happy Daze! Art

-- Art Welling (artw@lancnews.infi.net), June 07, 1999.

Voltage = Current (times) Resistance

V=IR

If your LED uses 20 milliamps you need a resistor

R=(4*1.5)/.02 (Four D Cell batteries at 1.5 Volts each)(20 milliamps)

R=300 ohms

Look at the rating on your LED's for the max current and use the equation above to compute the resistor... Have fun experimenting

Keep the faith

Helium

-- helium (heliumavid@yahoo.com), June 07, 1999.

HELIUM:

Tnx for filling in the Ohm's Law stuff -- newbies will appreciate it. My experience with the LED task lite project is that it's better to have the people drive a '20 milliamp' LED with something a bit less, for a margin of safety. I like 17 mills or so -- what do you think?

May your gas expand to Heaven,

Bill

-- William J. Schenker, MD (wjs@linkfast.net), June 08, 1999.

This company sells a white LED array flashlight that runs on 3-AA batteries for $34.95:

ccrane.com

There is also a nice article on making your own white LED flashlight in the current (June-July #71) issue of HomePower magazine.

You can get a copy at any big bookstore or download the current issue (with ads) for FREE at:

www.homepower.com

-- PLONK! (realaddress@hotmail.com), June 08, 1999.