<<<I'm guessing with variable contrast papers that until they are made for specific LED colors that VC won't be really feasible.Still I think LEDs will eventually replace fluorescent and incandescnet lighting in most applications.>>> The whole idea of using a panel made up of arrays of red, green and blue LEDs is that the output colour temperature can be smoothly adjusted to anything you want or need without problem. There are photos of array designs on one of the RIT websites, among other places. If I can find my bookmarks to them, I'll post them. Brightness (both overall and individual colours) can be controlled either by closed-loop current control or by duty cycle control with the advantage of duty cycle control being that you can hellaciously overdrive the LEDs for a few microseconds to get a lot more light than is possible in steady state operation. The lamps are pulsed for a few microseconds every few milliseconds so that both you and the photosensitive material see uninterrupted light. For an ophthalmic reseach instrument, I built a driver that hits an array of 12 "white" LEDs with 30 volts at 2 amps- for 1 microsecond at a time at anywhere from 10 to 1000 pulses per second. In either case, large, bright LED arrays are still nowhere near the low cost of a fluorescent lamp and proper diffuser. Want less light? Use more diffuser panels. bye, sid.
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