how can i automatically turn off the fluorescent lamp when i turn on an overhead projector?

Answer 1

There are wireless wall switches that replace the standard type. They retain the regular function, but have a remote you can keep at your projector. This would probably be the least complicated way. Check the home, hardware or better yet electrical supply store.

Answer 2

There are probably several ways to wire in a solution that could either react to the light in the projector or the current flow in the circuit going to the projector. But, you probably wouldn't want to have to run the wires to accomplish this task.

The simplest way I can think of would be to replace the existing switch with a switch that has remote capabilities. Then, place the remote next to the projector and use it as needed.

Without running new wiring, you might be able to get a wireless photo-eye that could be mounted behind the screen. It could be tweaked to only activate when the projector light was shining on the screen. You would have to replace the existing switch with a new switch that would react to the signal coming from the photo-eye. Again, something like that would be possible but probably more money or expense than you are willing to pay.

Of course, maybe someone else will have a real good idea that makes mine look stupid. I sure hope so.

Answer 3

Use an SCR power transistor circuit to control power to the fluorescent lamp and an amplified photocell to activate a relay (or another transistor) which would break the base current of the SCR and turn off the fluorescent light.
You could also use just the amplified photocell powering a relay, but it has to be a relay that can handle the fluorescent lamp transformer current.
There may be other simpler ways to do so.