[emersont49]

You might consider using a photo sensor connected to an analog port. Radio Shack used to have an assortment of them for a few bucks. It's been a while but I think I connected one side to the red (+5volts) and one side to the white. The resistance of the sensor should vary with light and that will, in turn, vary the voltage you see on the analog port (white lead).

Prior to connecting this to your expensive cRIO, you would want to do some bench testing on it. Connect the solar cell to a multimeter and read its resistance. Shine a light on it and see how that changes. See how much it changes if you block the sensor from ambient light.

This approach is cheap but it requires someone with some basic electrical skills (a knowledge of Ohm's law).

The problem will be that fact that the "balls" won't entirely total block the light.