Wow, I'm just feeling so useful this week
First off, it's a misnomer that LEDs don't dissipate heat. They do, but most people are used to single 20mA Radio Shack deals, so the heat is for all intents and purposes nonexistant. When you move up to the larger LEDs (1W, 5W, etc.), heat dissipation becomes a major issue.
Is this for close-up or distant camera work? Close-up is best, or distant within a tight area. For close-up work a large viewing angle LED will be best (60-90 degree), for distant spotlighting you'll want something much tighter(something in the 10-30 degree range would be best).
I do not know how much power those plug-in halogens suck down, but you need to be careful running this off of the same battery as the camera. That being said, you will more than likely get a higher efficiency out of the LED versus the halogen if the conditions in my last paragraph are met.
Keith's cost breakdown is a bit overpriced, IMO, so here's my breakdown. Luxeon 1W white LEDs (
, just do a Google search on Luxeon and you'll find plenty of resellers) can be had in qty. 1 for about $5, less in bulk (say 10). For a 12V battery, I'd say put three of these in series.
For a driver, stay away from resistors. You need current control, and voltage regulators already have that functionality built in. Pick up a 12V regulator, like the LM317 ($0.50?), and connect it up as a current regulator. To do this, instead of connecting the ground pin to ground, connect it to the output through a resistor (I'll leave the value calculation for later). Now, no matter what voltage your camera battery drops to (within the range of the LEDs), the LEDs will always get the same amoun of current, say 200mA.
For heat dissipation, mount the LEDs to a metal heatsink, but if you keep the current low enough the metal core board they come on will more than likely do enough cooling without any extra help.
Board layout is now a 30-60 minute job. Proto boards can be had cheap, if you know where to look. Try out
, it's a $10 setup fee + S/H and $2.50/square inch... for small boards, it doesn't get any cheaper than that. If the board comes up larger, but you can keep it one-sided, go to
and get their one-sided proto for $20 + S/H.
I imagine with two strings of 3 series LEDs, a PCB, and regulator, you're looking at well under $100. Let us know how this one turns out.
Oh, and my comments about LED spectra and CCD cameras from the thread Keith linked to still hold...
Dan - Owner