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Solar Lighting


Louis Hom

Jan 1, 1970
I know it would be easier to buy a new one, but I want to learn about
this. We have a box that charges 2 AAs during the day with a little
photovoltaic cell, then illuminates our house numbers (yellow LEDs) at
night. It stopped working, and I found that jumping the wires across the
light sensor turns on the lights. So I'm guessing that's the flawed
component. The little circuit board is buried beneath some opaque epoxy
or silicone-like material.

So first, what is the name of the component I need to replace? Photocell?
Photodiode? I'm all mixed up because I read that photocells have low
resistance in light and high resistance in the dark . . . how do you turn
on current flow by increasing resistance?

My neighbor also gave me his failed solar-powered fluorescent light
(collector is about 6"x8", with a 6V sealed lead acid battery), that I'd
like to turn into a white LED system. Do I need more than the solar
panel, battery, LEDs, diode to prevent back current into the panel, and a
photocell to turn on the LEDs at the appropriate time?


Jan 1, 1970
It sounds like you're describing a cadmium sulphide Light Dependant Resistor
(LDR). They are usually the problem in failed light sensing switches. Have a
look at this web site for a sketch of one, and a descripition of how they
work. There's even a schematic showing how to use one to turn on an LED. It
should answer all of your questions.

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