Subject: Why is film ruined when exposed to yellow light?

Out of curiosity I would like to understand why photographic film can be 
handled in a "dark room" lighted with red light but is ruined if it is 
exposed to the same intensity of yellow light. In a movie, I was watching, 
some people were looking at some film in a dark room. They kept 
saying, "Make sure no one opens the door." I don't understand why regular 
yellow light would harm a photo. 

Re: Why is film ruined when exposed to yellow light?