Traffic lights

Years ago while I was at the Exploratorium Teacher Institute an employee came in and had managed to get a bunch of real life traffic lights. They had asked a city worker who was changing them out what they were going to do with them and ended up walking away with a lot. I took home two green and one red and unfortunately left them to sit in a box all these years. I finally managed to check with Zeke Kossover about wiring them up and was surprised to learn that they ran off only 120 V. I had it in my head that they would need much more and I would have to use a transformer. So I bought a heavy duty plug for each light and hooked them up. You can find traffic lights of all varieties on eBay. It was very easy and now I have three giant lights!

I'm not quite sure what I will do with them but I have some ideas:
- Use the red and green lights to indicate to students when to keep working and when to stop on an activity.
- Use the red and green for a giant Colored Shadows demo (I haven't tested if this works yet).
- Have students use light sensors to investigate the light intensity at different distances. I expect that this is bright enough students from all over the classroom will be able to take data off this one light source. 

What are some other ideas about what I could do?