[oc]

I've used the beep test in PE classes that I teach before, it's a great test. Sorry Welsh there is no light. This Wikipedia article listed looks spot on.
I also coach CC and have used it with my runners. As you progress through the levels it moves past an endurance test to a speed test. I am in pretty good shape and can run for quite a while-but at the higher levels of this test you might have the endurance to keep jogging at a comfortable pace for miles on end-but if you don't have the foot speed to keep up this test will spit you out.