The rechargeable battery is replenished by the solar cell which creates electricity when the ceiling fan's lamp is on. When the lamp is off the photoresistor detects the darkness and signals the control circuit to turn the LED on.Here's a close-up video of the light-up handle in action.Here's a video showing how easy the handle is to find in a dark room.Final Thoughts
I was afraid that putting the circuit board in the diffuser bowl so close to the hot lamps would create a fire hazard, but after replacing the lamps with CFLs and measuring the temperature in the bowl I concluded that it was probably safe. I was also worried about some part of the circuit accidentally contacting mains and electrifying the pull chain or starting a fire. However, there seems to be enough room in the bowl and the pull switch is constructed such that accidentally contacting mains appears unlikely. However, these risks are real possibilities and you follow this instructable at your own peril. You are responsible for your own safety. The reason I've left the original instructable intact is because I feel it is much safer and its installation step is both easier and depends less on having a specific type of lighting fixture.
If I were to redesign this as a product to be sold, I would look into making a new pull chain switch that has an integrated AC to DC converter and a new pull cord that can deliver power to the LED in the pull handle while standing up to the wear of being pulled on many times a day for years. The idea of a lighted pull chain handle has been patented since at least 2001. Maybe the engineering challenges of designing it to be safe while still being economical aren't realizable.
Oddly, after a period of time the LED cuts off even if the battery still holds a good charge. Since the intent of the original garden light was for decorative purposes and not providing illumination, I'm guessing that there is a timer that controls how long the LED stays on so that it doesn't shine late at night when no one is around to appreciate it, but this is only a guess. Additionally, given that the LED puts out more light than needed and changes colors constantly it may disrupt sleep. A solar garden light meant to provide illumination throughout the night paired with a high efficiency red LED, which will help preserve night vision, may be a better solution.Bonus Hack
: In the planning stages of this project I considered using the pull chain as part of the return leg of the LED's circuit. So I connected the pull chain to a multimeter and selected the continuity test; it showed an open circuit. However, when I pulled the chain tight the resistance drop to only a few ohms. Therefore, if you need a simple on/off stretch sensor, then using a pull chain might not be a bad option.LinksHow a Solar Garden Light WorksPortfolio Stainless Steel Solar-Powered LED Path Light (Item #: 329346 | Model #: 00942)Harbor Breeze Brushed Nickel Ceiling Fan Pull Chain (Item #: 101858 | Model #: FP5)