photo cell or light activated switch

Of course it's possible, for some specified meaning of "exact same" (pico-, nano-, micro-, milli-second scale repeatability?).

However, for an arbitrary traffic light in an arbitrary location at an arbitrary intersection, for a vehicle at an arbitrary location in the line of an arbitrary mix of types and sizes of stopped vehicles, in arbitrary weather conditions, where there's a arbitrary number and type of potentially interfering light sources and reflections, it's a rather challenging problem. It's certainly solvable (most drivers manage it with some degree of success) but not trivial.

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Rich Webb     Norfolk, VA

Exactly the same,meaning to the .0001 of a second, the same. The light activated switch would only have one LED bulb about 30 ft. away. I was only using traffic light an an example of the type LED bulb that the Light activated swithch would be triggering off of. The light activated switch would need to trigger a ground circuit at exactly (.

0001) the same time every time a LED bulb is turned on. Any ideas to how this can be done?

Well, a photodiode with an appropriate filter on the front end, wired to a FET opamp set up in a transimpedance configuration would probably be a good start. That's basically what makes up the guts of the IR receiver section of devices with IR remote controls and they can work out to that distance (some of them, on a good day).

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Rich Webb     Norfolk, VA

thanks man thats at least a starting point for me to figure out how to make this project work.