> the only light I had was green and red. I can't explain how the 2 made white.

> It's digital (Canon 30D), the exposure was 5 minutes 49 seconds with auto-white balance.


Given that there was no light present except that coming from the signal; and being a signal engineer, I would venture to guess you got white because the "green" really isn't a true green at all.

While the red is pure red, standard yellow and green signal colors were ergonomically designed by the A.A.R. around the actual spectral response of the normal human eye; to minimize the chance of confusing yellow for green, or red for yellow. Thus the green is actually a specified mixture of green with blue mixed in.

You actually had green and blue from the top head, and red from the lower head. Thus you had all three primary colors present, and since the scattered light mixed, white was in the ambient light. Your magical camera, with its "auto white balance" did the rest.

I hope this helps. Aren't digital cameras truly amazing!

OPB