Need help designing an LED light

Hello all. I'm new to this forum. Very cool-
Unfortunately my computer won't run the designer program. I'm designing a LED light with either 3, or more preferably 5 or 7 leds. I'd prefer a 6V input but could use 9 or 12 volts. I need to know what size resistors to use.

Also do I wire the LEDs in series or in parallel? I'm planning on using cr123's (3V w/ 1300 to 1500 mAh). I'm shooting for a runtime of 16 to 20 hours. Longer runtimes are not necessary and I need to maximize brightness. I would be willing to accept runtimes of 8 to 10 hours, if its not bright enough.

I'm not sure (newbie), but I was considering using 30 mA 3.4 to 4.0 V LEDs, 6000 mcd.

I'm trying to make an area light (bright enought to light up a small room). What should the viewing angle be? I was thinking 30 to 50 degrees. How do I wire them and what type of resistors do I use?

Any help or suggestions would be greatly appreciated.

Thanks

there are some great little drivers for low-power LEDs that will run up to 4 'banks' of LEDs at 30mA... they will give you constant brightness.. there is about 7.5WH of energy in a 123 if you drain them slow enough (more like 3 the way we typical cpfers over drive them)...

quick bit o math says a 30mA 3.5Vf LED is about 1/10th of a Watt.. means.. you can run 7 for just about 10 hrs on (1) 123 cell.. so you are right in the zone on your runtime desire i think.

I would look on microchip's website and linear's website for 'white LED driver' or just start with 'white led'.... in the process of searching for 'high power' drivers (not much luck there).. found several very nice driver ckts that will do exactly what you want.. often you can acquire samples at no cost, else they are cheap with a shipping caveat.

In any event.. i personally would definitely work out some ckt that will run them in series or banks of a couple in series.. LEDs like that will be noticeably different brightness if run in parallel.

.75W will not be mind-blowing bright.. so what amt. of light are you looking for in a room? It will be a nice amt of ambient light, but probably not the amt. you'd want for working. (of course i'm spoiled with at 12W worklight I built and a 1.8W AAA light)

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andrewwynn said:
.. there is about 7.5WH of energy in a 123 if you drain them slow enough (more like 3 the way we typical cpfers over drive them)...


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Andrew, I dunno about that 7.5 Whr figure. It appears that 4 Whr is a better low rate figure for a good CR123 cell.
Checkout the datasheet for the Duracell 123 below
123 Datasheet

oops.. thanks for the correction.. i've always just thought that due to over driving. that as typical.. 1/2 the energy was lost from heating the battery with internal resistance.. i found the error..

I used this page as my reference and it mistakenly uses 6V for the voltage on the 123 cell so there is an error of 2x... so.. how about.. 3.9WH in a 123 cell.. guess you need two cells... you might want a brightness dial on that light /ubbthreads/images/graemlins/wink.gif

-awr

ps.. dang do i really only have 471 posts... where do you guys in the 1000s have the time /ubbthreads/images/graemlins/wink.gif cpf is awesome for people checking up on you, thanks Doug for helping me find that error.