Thursday, November 09, 2006

LED as a Light Sensor and more....

Recently got interested in the use of a normal LED as a light sensor. Its amazing, but there seems to be some conspiracy on the part of the electronics professionals, in keeping this interesting and wonderful physical phenomenon, hidden from public. Or is it ignorance?

Just take a normal voltmeter (or a digital multimeter) and connect the two terminals of any (say red) LED to the voltmeter. Cover the LED with your hands and note the voltage on the voltmeter. It should read close to 0. Now expose this LED to bright light. What do you observe?

The only book that talks about this is by Forrest Mims.

We just published a Design Idea in EDN on this topic.

The natural extension to the idea of LED as a touch sensor, is to use commonly available 5x7 or 8x8 LED matrix displays as a touch panel. We have been toying with this idea for some time now and have made some interesting progress. Its not very straight forward, but we are getting there...

Dhananjay Gadre


Anonymous Forrest M. Mims III said...


Glad to know you have learned about using LEDs as photodiodes. Very few articles discuss this, although I've covered it in some detail in various books and scientific papers. The GLOBE sun photometer is based on my original unit in which LEDs serve as spectrally-selective photodiodes. That unit was built in 1989 and is still in use. It is highly stable over time.

Please see my web sites ( and for publications related to this. I'll try to add a new section on the topic when time permits.

Forrest M. Mims III

8:53 AM, November 09, 2006  
Anonymous Anonymous said...

Dhananjay, using LED as light sensor is not a new thing ... this has been used by many projects throughout the world by many engineers and students ... if I remember I used the same thing when I was doing my diploma ...

One more thing, there are several such type of things where reverse process works ... such as using loudspeaker as microphone ... using transmit antenna as receiving one ... etc ...

Anyway, may be you are right, these are to a large extent hidden from general public ... good work done to post it on your blog site ...


5:21 AM, July 17, 2007  
Anonymous Anonymous said...

My friend and I were recently talking about technology, and how integrated it has become to our daily lives. Reading this post makes me think back to that debate we had, and just how inseparable from electronics we have all become.

I don't mean this in a bad way, of course! Ethical concerns aside... I just hope that as technology further advances, the possibility of transferring our brains onto a digital medium becomes a true reality. It's one of the things I really wish I could encounter in my lifetime.

(Posted on Nintendo DS running [url=]R4i SDHC[/url] DS scPost)

9:53 PM, January 31, 2010  

Post a Comment

<< Home