Why do they use different colored lights in theatre?
 

Just saw a Julius Ceaser production with my son and we had seats in the front row on the side and I noticed for the first time all the lights were different colors. Green. Red. Couple different purples. What's the philosophy behind this? Is this something big productions do in Hollywood?

With red, green, and blue colored lights on dimmers they can make any color they want. Dim the green and you get purple and any other combination you want. I'm not sure why they would have purple lights unless it was for a specific purpose in that production. Different colors convey different emotions and sometimes different areas of the stage are lit differently to create distance or change the tone of certain characters. I am no stage lighting expert but these are my observations. Actually, I think a class/book on stage lighting would be helpful to videographers since they really have worked out the emotional effects of lighting techniques.

Here's a page from Rosco on using colors on stage:
http://www.rosco.com/us/technotes/fi...technote_1.asp

Same page in pdf format:
http://groups.northwestern.edu/lovers/docs/Lights28.pdf

Here are more technotes pages from Rosco that give a lot of basic information:
http://www.rosco.com/us/technotes/filters/

In basic flat stage lighting, sometimes lights coming from one side will be a color different from light coming from the other side to create the a 3d illusion. The side with the bluer/lavender light bill look as in shadow and the amber/yellow side will look like the key side. It is setup so the effect is more subtle than obvious.

I knew there was a reason but I didn't realize it would be so intricate.

Jack, those links were fascinating. Thanks. I think I will order a few filters and mess around with different colored lights and see what happens.