Back in my misspent youth, I was a stage lighting geek. Lots of time on ladders with a speed wrench, hours poring over swatches of filters with names like “Surprise Pink” and “1/4 CT Blue”. So years later, when I saw an old 6″ Fresnel in a junk shop I had to have it. And it hung there in the basement ever after, reproaching me for not doing something with it.
Until I saw a high-power RGB LED at Adafruit. After a few false starts (should have read the detailed triple-LED-driver specs and discovered before I bought it that it doesn’t do common anode) I rolled my own way-too-simple driver from three MOSFETs and some 5-ohm resistors and mounted the whole thing where the fresnel’s mirror used to go (LEDs already point all their light forward).
For control, I’ve got an arduino clone that claims to supply two amps of spare power and a little proto-board with three potentiometers. So it’s just like an old-fashioned stage light: set the color and forget.
Does it cast enough photons to be useful? Maybe. I haven’t cranked it up to full power yet; I’m a bit scared. But at least it’s one less project cluttering up the workshop and my brain.