Use this device to identify energy inefficient light fixtures by their low frequency flickering! All you do is spin the top and look for a blinking bluish line to see if you could be using a better light fixture! Why This works: Fluorescent light bulbs flicker at twice the AC frequency because the magnetic ballast driving them is directly affected by the AC current peaks. So 60 Hz AC = 120 Hz flicker. Newer more efficient solid state fluorescent tube lights flicker at a much faster rate. This top has high contrasting colors spaced in such a way that when spun at low speed it will create a frame rate interference, just like when you look at your TV through a digital camera. The photos taken with the bluish lines are what you see with slow flickering light, the other two photos used sunlight which doesn't flicker and just makes a red white blur. NOTE: Some LED's have low flicker rates and will give you a false positive. Don't throw away your energy efficient LED's!