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LED as ambient light sensor

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Mosaic

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Hi, i want to adc sample an LED to use it as a light sensor as opposed to a CDs cell.
Any advice on this approach?
 
You can use a led as a proximity switch, pulse the led on and then look for a light reflection.
The capacitance of a led is changed by ambient light, what I'm getting at is that you can measure ambient with a led by measuring its capacitance, I cant remmeber if you forward or reverse bias the led, but if you charge its capacitance via a high value resistor you'll be able to measure the charge time, and therfore the capacitance, ie ambient light.
If you google it you'll find some applications, adapting one shouldnt be difficult.
If you have a capacitance bridge have a play around.
 
Hi,

Probably better off using a light sensor or photo cell because they will have more sensitivity.
 
An ordinary diode in a clear glass case like a 1N4148 senses light. I had a circuit that messed up when it was not enclosed due to it picking up light.
 
So an led generates a current from light too.
 
I can't find it now but.....EDN magazine had a project where a night light, put light out through a LED. Then about 100 times a second the light was interrupted and the LED was used as a light sensor. I think they used a 6 or 8 pin PIC.
 
So an led generates a current from light too.
Take a green LED and connect it to a DMM, then shine a light at the LED. Under bright light, it will generate a couple of volts, similar to a photovoltaic cell. Green LED's seem to work best. I expect the actual current will be in the microamp range, since the die is often the size of a grain of sand.
 
I've done a solar tracker, but it used cds photocells.
 
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