Traffic Fairies

On the corner of College Ave. and Allen Street, there hangs a traffic light. Observing the light rotate between cycles of green, yellow, and red I wonder: how does the light 'know' when to change? Intrigued and puzzled I went back to my room, logged onto Google, and looked up 'How a Traffic Light Works'. I came across a very reliable source: Dr. Kelsie Walsh of the Hawaiian Traffic Institution. Dr. Walsh's thesis describes exactly how traffic lights work, how they 'know' when to change colors and the secrets behind the three colored hanging light. "Fairies", Dr. Walsh explains, "Fairies are the magic behind the source of light. In each circle, there lives traffic fairies. Each fairy sprinkles red, yellow, and green dust on the lights. The dust reflects off the light and points at the oncoming traffic. There is a fairy leader that tells each fairy when to sprinkle their dust on the bulb. The green fairy is the highest ranked fairy and gets to sprinkle the light for 30 seconds. Then, following behind him is the red fairy for 25 seconds and the yellow fairy's shift is only 7 seconds". So, Dr. Walsh answered my question; however, now I want to know: where do the fairies come from?