How do solar garden lights work

asks PDTV:
A. Solar garden lights generate and store their individual power during the day and release that power at night. They can be placed in any site that get direct sunlight.

Q. What are they made of
A. A solar light contains a solar cell, a single battery, a small controller board, an LED light source and a photoresistor to detect darkness.

Q. How does it work
A. A single solar cell produces a maximum of 0.45 volts. A garden light would usually use four cells, producing a total of 1.8 volts and a maximum of about 100 milliamps after full sunlight. The solar cells are wired directly to the battery through a diode (which prevents the battery's current from flowing back through the solar cell at night). The battery is a standard AA Nicad battery, which can supply about 1.2 volts and can store a maximum of about 700 milliamp-hours.

Q. What happens at night
A. The solar cells stop producing power and the photoresistor turns on the LED, which produces about half as much light as a candle. A fully charged battery can operate the LED for about 15 hours.

Q. That's not very much light, is it
A. No. You wouldn't expect to be able to read by these lights. They are designed more to indicate a path or drive than illuminate any area.

Q. But they're so expensive...
A. That's because the solar cells, which are made from silicon crystals, are costly. It's possible to buy even more expensive solar lights which use a combination of LED and a halogen flashlight bulb which comes on for a minute when a motion sensor detects movement.

However, solar garden lights have the distinct advantage of needing no wiring, and can be used in fairly inaccessible place - it only takes a few seconds to put one in place.

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By Sheena Miller