The third lesson I learned was that angle affects reflection. We're all taught in middle school science class that light bounces off of objects at the same angle that it hits, but for me at least, I had never really thought about how that rule applied to objects that didn't have a mirror surface. Unsurprisingly, it holds there as well.
For this show, I used a light yellow-green color (Straw Tint, I think) from one angle and a pinkish color (I don't remember the name) from the other angle. The pink and the green combined to create white, and the end result was a warm, comforting light that brought out the warmth of the actors' skin tones. The set, which was mainly a warm yellow, looked very good. However, there was one wall of the stage that didn't look like there was any of the pink color hitting it at all; it had kind of a radioactive green glow to it, even though I was certain that there were two colors of light shining on it.
I finally figured out that the wall looked radioactive because it was slanted. It was at about a 45-degree angle to the audience, so when I shined two lights onto it from 45-degree angles, one light was perpendicular to the wall surface, while the other was barely skimming along that surface. The yellow-green light was the one perpendicular to the wall surface, so its color reflected more toward the audience, while the pink light reflected into the back stage area.
The solution? Switch the gels between the two lights hitting the wall. Then any actors standing in front of the wall were still illuminated by both colors, but now the pink light was hitting the wall straight on, while the yellow-green was reflecting backstage. The pink light looked much less garish than the yellow-green, so this toned down the wall while keeping the acting space colored the same way as everything else.