Ok, this movie I watched as part of my science class. It is a 1980's-90's PBS Sci-fi mini series about light.
I think there was at least 6 episodes. It was a live action, and the show was about 4 kids.
If I remember right it was staged in a barren desert like place or planet.
The thing I remember most though is how they had to find this giant ruby pendant about the size of a person's palm to either make a laser, or fire a laser, at the bad guy destroying him.