Light sensors

[Bush]

Hi, I want to make a simple circuit to power an LED. I want the led to turn on when a light sensor detects the absence of light. I'm wondering if anyone knows of a small light sensor I could use for this, one similar to those found in night lights. Thanks!

[Pkmnjunky7]

You could possibly apart a night light and use that in combination of one of the night light bulbs that have leds in them. They sell bulbs that have like 3 white leds in them.

[jdmlight]

It's a really simple voltage divider circuit.

If you do the second of those circuits (the one with the photoresistor as R2), the voltage out the middle pin will increase as the amount of light decreases.

I would grab a random photoresistor then use a potentiometer for R1, so that you can adjust the sensitivity.

[Mario]

A dark sensor? EMSL has a great simple one:
http://www.evilmadscientist.com/article.php/nightlight" onclick="window.open(this.href);return false;

This circuit also works with a photoresistor (CDS cell) but it's best with a phototransistor.