Students love this demo!!!Assembled and tested. Requires 9-volt battery. A red and a green LED are packaged in the same bulb. First use the DC Source and demonstrate by switching polarities - current in one direction activates the red LED, current in the other direction activates the green LED. The bulb at the end of a 6-foot (1.8m) flexible cord, so it can be twirled in a circle. You get a nice, continuous red or green circle, depending on the current direction. So the question is this: what happens when you hook it up to the 9-volt AC source provided?!! Could it be the 'third color'? Instructions© included.