cant figure out leds...

ShaolinDrunkard · Post by **ShaolinDrunkard** » Sun Jan 08, 2006 3:34 pm

I've seen many different sizes and brightnesses of leds around, and I gotta say, I dont really understand them. For instance.

How do I figure out which resistor to use with a particular led, I mean do larger brighter leds, require less of a resistor?

Also, resistors go by OHMs, how do i know that a particular size resitor is going to work with my particular nattery voltage?

and lastly, I hear it doesnt matter if you put the resistor in the positve line or the negative, question is, do I need a resistor for each led or just one hooked up between the battery and all of them?

I ask this because I've recently become interested in modifying regular flashlights with leds. The power was out at my house recently for a week, and all I had was a crappy basic style flashlight, I had to shake the thing to get it to work half the time. I hear leds are a lot brighter, last longer and have much better battery life then standard flashlight bulbs... there are a lot of different ones out there and I think i want to use the brightest I can find and I'm not sure how to figure out which resitor to pick up for them because I might be using different types of batteries on each one.

Thanks ahead of time.

Post by **Gamelver** » Sun Jan 08, 2006 3:46 pm

first, you gotta get the specs for whatever LEDs you're using. Vf is voltage that the LEDs use, and If is the current that they use. To know which resistor to use (in series with the LEDs) use this LED resistor calculator

. use the parallel LED one (at the bottom) and simply insert the Vf, If, and amount of LEDs you want to use. Then wire it as they show there.

timmeh87 · Post by **timmeh87** » Sun Jan 08, 2006 4:51 pm

it would be cool to use a variable resistor (potentiometer) to control the brightness. that way you could use it at a dimmer brightness for longer, if you needed to.

this might be useful to you:

http://members.misty.com/don/led.html

Post by **Gamelver** » Sun Jan 08, 2006 9:00 pm

as long as you had some way to stop the resitance from getting too low, then that'd be pretty cool, yeah

.

timmeh87 · Post by **timmeh87** » Sun Jan 08, 2006 10:14 pm

a normal resistor in series with it

Post by **Gamelver** » Sun Jan 08, 2006 10:20 pm

oh yeah

...

ShaolinDrunkard · Post by **ShaolinDrunkard** » Mon Jan 09, 2006 10:18 am

Thanks guys.

daguuy · Post by **daguuy** » Mon Jan 09, 2006 5:00 pm

what if the LED has a very low volatge rating. would a resistor get the voltage low enough for it?