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Light Sensor identification? Answered

Hello all,
I've just started a project and found a spare light sensor in a Megabrite LED Color Changing Night Light. However I am a complete novice and do not know how I use this specific light sensor.
So here's the question: Are all light sensors the same? Can i just use any lightsensor 'ible or do I need specifics for this sensor? And if so, does anyone know how I can figure out what the light sensor is?
Thanks for any help.


Not all light sensors are the same.  So part of this game is figuring out what kind of light sensor you've got there.

I don't know for sure, but I am going to guess that this sensor is a photoresistor. Sometimes this is called a CdS cell, where Cd-S stands for cadmium sulfide, a material whose electrical resistance changes in response to light. 

This type of light sensor has a certain appearance, with wire traces that look kind of like two combs stuck together, like the one in the picture here:

If your light sensor looks like that one, then it's probably a photoresistor, aka CdS cell, aka light dependent resistor (LDR).

Oh wow, that's fantastic! Thank you.
So next question is, is there any specific way i should handle this? How would i know how much resistance i should put to powering it? etc

Try connecting it to a multimeter on the resistance setting, i.e. as an ohmmeter, and then measuring the resistance through it, in response to different amounts of light.

I think these things typically have a resistance of around a few Kohm, in light bright enough to see by, and around a few Mohm in darkness.  Some pictures of this are attached. I was using the cap from a Sharpie(r) pen to block out light for the darkness-test.  For that picture, I do not have the cap completely on the LDR, so I'm letting a little bit of light in, but that's because I wanted the meter to say something.  The highest resistance it can measure is 2000 Kohm = 2 Mohm.  When the cap was completely on, the LDR was offering resistance higher than 2 Mohm; i.e. out of range.

Assuming you want to connect device to an external circuit, one way to do this...

...is to make this LDR be one side of a voltage divider. You pick the other resistor in the voltage divider so that it has a resistance in the middle of the range in which you are interested. As a guess, maybe this other resistor would have a value of about 10K.  The point of doing this is so that the output from the divider is a voltage signal.  Then you have some other circuit that watches that voltage, and I sort of drew a circuit diagram of how I imagine this might work.