Hope you're all having a great summer, and hope this stirs the waters a bit.
I have been busy researching a third-gen bookscanner, probably incorporating LED lighting. I've read thousands of posts over at candlepowerforums
over the last few years, mostly because I love LED flashlights. I want to convert some of that wasted time into a usable lighting system, but things aren't looking good yet.
At the moment, I have 4 Cree Q5 LEDs
, and 4 1A drivers
. In principle, with that kind of power, I should have around 700 lumens at the emitters, and some fraction of that on the book surface.
It looks like things are not so simple, though. My first observation is that despite the ridiculous current these things are drawing, and the insane heat they are producing, they are not actually that bright. Now, if you put some kind of focusing lens on them, they are very bright, because the light is concentrated in a small area. However, for this application, that won't work, because we need diffuse, even light. Another potential problem is that the current draw rises with temperature, probably causing the luminous output to droop.
It would be possible to get relatively even light if you were using many, many LEDs and some optics, but that would be expensive. The cheapest you can do one LED&driver combo is about $8, and each one draws 1 amp, so you're looking at a 16 amp, 5V power supply, and the necessary heat dissipation, and so on. There might be a better, cheaper way to drive them. I will be consulting with my friend Wolfgang, the ELECTRONICS GENIUS, about this.
For now, I'm just going to post a bunch of pictures here. We have a very nice photometer at work (a Minolta LS-110), and I'm going to measure the actual luminous output of the halogens I'm so fond of and compare it to the luminous output of these LEDs.