DaveNagy
Newly Enlightened
I think this sounds like a really interesting idea. Put me down for two! 
Some random thoughts:
No optics, so we're talking a total flood "beam", right? In that sort of configuration, I'd say, "The more lumens, the better." (Within reason.) My Zebralight has a 120 degree beam, and running flat out, it does 70 lumens or so on high. That's a pleasing and ample amount of light for working on a car, or cooking a meal, but it's certainly not "excessive" seeming. (It would be excessive for something like map reading.) My Zebralight does about 12 lumens on medium, and frankly, that seems barely adequate for doing things at arm's length. 20 lumens might be better. (Basically, I'm trying to say that you shouldn't try to compare a focused beam to a an unfocused one of the same "strength".)
Some of the switch ideas be bandied about in this thread sound waaaaay too clever for their own good. Just put a plain old fashioned mechanical switch on the thing and call it done. Something tiny that you could operate with a fingernail would be fine. Seems like you'd want to put it on the edge of the card somewhere, so it could stick out a bit and yet not add any thickness. (Notch the edge of the card where the switch is if you don't the switch to extend beyond the "footprint" of a normal credit card.) Some sort of thumbwheel would be neat and would fit well with the circular theme you've got going. Ooo, and you could possibly do some sort of variable brightness that way!
(I'm talking about the sort of switch like old transistor radios had. You could adjust the volume continuously, but they also "clicked" off when rotated all the way "down". The rotating part of the switch was probably about the size of a US nickle, but only a tiny fraction of it stuck out of the case. You know, kinda like an inline lamp-cord switch?)
I have no idea whether such a switch exists in a sufficiently thin form-factor, regrettably.
Some random thoughts:
No optics, so we're talking a total flood "beam", right? In that sort of configuration, I'd say, "The more lumens, the better." (Within reason.) My Zebralight has a 120 degree beam, and running flat out, it does 70 lumens or so on high. That's a pleasing and ample amount of light for working on a car, or cooking a meal, but it's certainly not "excessive" seeming. (It would be excessive for something like map reading.) My Zebralight does about 12 lumens on medium, and frankly, that seems barely adequate for doing things at arm's length. 20 lumens might be better. (Basically, I'm trying to say that you shouldn't try to compare a focused beam to a an unfocused one of the same "strength".)
Some of the switch ideas be bandied about in this thread sound waaaaay too clever for their own good. Just put a plain old fashioned mechanical switch on the thing and call it done.
Something tiny that you could operate with a fingernail would be fine. Seems like you'd want to put it on the edge of the card somewhere, so it could stick out a bit and yet not add any thickness. (Notch the edge of the card where the switch is if you don't the switch to extend beyond the "footprint" of a normal credit card.) Some sort of thumbwheel would be neat and would fit well with the circular theme you've got going. Ooo, and you could possibly do some sort of variable brightness that way!(I'm talking about the sort of switch like old transistor radios had. You could adjust the volume continuously, but they also "clicked" off when rotated all the way "down". The rotating part of the switch was probably about the size of a US nickle, but only a tiny fraction of it stuck out of the case. You know, kinda like an inline lamp-cord switch?)
I have no idea whether such a switch exists in a sufficiently thin form-factor, regrettably.
