Start with this circuit pictured in the image gallery.
Walk around and find different sources of energy. For example: Hold your circuit to the sun or light bulbs or in the dark. Record your findings in table. If you have trouble seeing the numbers change, adjust sensitivity with screwdriver.
Move the sensor closer or farther from the energy source. Record your observations in a table.
Can you see any energy coming from a TV remote control? What happens if you point it at the energy meter and press a button? (hint: most remotes have IR LEDs)