Turn LED into light sensor?

Question

what is the cheapest way to turn a green led into a green light sensor?

Answer 1

The simplest way is to shine a light on it and measure the voltage produced at the leads.  You won't get much response, though, as the LED isn't designed to be a sensor.  It will work, but it will be extremely inefficient.

Normal photodiodes have *huge* surface areas to collect light, and solar cells have even larger surface areas to collect light.  The surface area of an LED is tiny compared with a photodiode, so that's why the output will be so small when you shine light on it.

As for the green color, the green plastic filter will work as a color filter.

.

Answer 2

Might take a look at this project and what I would have recommended for use as a light sensor:

http://www.robotroom.com/Comparator.html

Ron