LEDs as light sensors

LEDs are great for making light, but they can sense light too!

I recently stumbled upon this site which mentions, "In 1977, Forrest M. Mims reminds us in one of his "Engineer's Notebooks" that LEDs can also be used as photodiodes... " The page features a LED matrix being used as a multi-touch input but offers very little information. I still have no idea how to make his project, but I did learn how to use LEDs as light sensors.

This instructable goes over my experimenting with different kinds of LEDs as light sensors and making a dark activated night light using LEDs as sensors.

Step 1 What You Will Need

• random assortment of LEDs
• current limiting resistors for LEDs
• multimeter
• breadboard
• bright flashlight
• microcontroller (I used Arduino)

Comments

[T-Urn]

Nice experiment! I came across this about 20 years ago - my then Boss pointed me at it as a sensor for a low level light meter - there wasn't enough output :-( Don't think I've never seen it used in a product. Out of the companys collection of LEDs I remember the high bright red LEDs ( clear case ) worked best. It also got a mention in the April copy of Elektor Mag this year I believe - there was a follow up letter asking if it was an "April Fool". There was no consensus as to which type of LED gave the best output. I've just tried it with a Hyper brite red LED in a water clear case - its about a year old, and I'm sorry I can't tell the Manu or Model. I stuck it under a halogen desk lamp, 20 Watt, not diffused, about 1 foot / 300mm above. Got about 600mV or about 0.7uA peak on a cheap DVM. Readings dithered a bit. Not sure why - may have been poor contact with crock clips etc.

[Electorials]

Oh 1.381V, that's a lot!
I knew they could be used as light sensors, but I didn't know they could produce a voltage that high.

Can you light another LED with the generated voltage from the first LED?
haha

and also, I thought your name was Zornik, a Belgian band, but it's Zorink :D
Do you know Zornik?

[Zorink]

I have not been able to light up another LED, but I'm sure you could if you string enough together. The voltage is great for an analog input pin on an IC, but the current isn't enough to drive an LED.

I am unfamiliar with the band, I'll have to look them up!

[munymuny200]

r those black leds if so where can i get them

[micobanff]

They are infrared LEDs... they are more commonly clear cases.
Most online LED suppliers will have infrared LEDs, not sure which ones will have coloured casings.

[wild_blaze]

btw i got 0.33 volts from a green LED........

[wild_blaze]

just watchd d video......i think...u really don't need an arduino...or any microcontroller for that........btw nice concept............

[lukeD]

I've got a question:
can I use a normal LED to make a security system?

my plan was to make it in my room. a laser light pointing at the LED and if the laser beam is interrupted (if the door is open, or if somebody walks by) that I can see that somebody was in my room.
would this whole plan be possible with a normal LED?

[Zorink]

It would work okay, but I'd use a component that is actually made to be a photo-detector. I've seen it done with IR or lasers depending on the distance you need. For just a door an IR LED with an IR detector would work as long as there are no other large sources of IR near it (certain lights, the sun, etc shining on the sensor).

Here is one I found with a bit of google
http://hackaday.com/2011/04/19/laser-trip-wire-the-bare-essentials/

[lukeD]

can you find a IR detector in household stuff?

[Zorink]

They are pretty cheap. I think Radio Shack has them for a few bucks.

[lukeD]

rated *5

[kcd12321]

Really interesting and cool. The straw had a great effect.

[beehard44]

i was wondering if i can make an earpiece out of this (passive receiver) but i doubt if the LEDs can supply enough power. i'll try it tho

[Electronics Blurred]

Because , like diodes ,
diodes were able to be turned into electricity generating stuff .
Now , if you are worried about it not producing enough voltage , use a op-amp , this site , is so freaking clever .
http://www.wikihow.com/Make-a-Motion-Detector
i didn't say it's the best , there might be more ,

[Zorink]

opamps are magic

[Chowmix12]

LED solar panel FTW!!

[strmrnnr]

I may have to play with this idea some day. The current may show up if a load is introduced.

I wonder how many LEDs it would take collecting light to power 1 LED emitting light at full power.

[Ender2007]

Very nice!
Thanks.

[billbillt]

This is great! Could you maybe provide a simple hook up diagram or schematic?
                                   Thanks!

[scratchr]

This only uses 2 leds, 2 transistors, and a 9v.

[billbillt]

Thanks for this!

[madepablo]

Great tutorial!

However, could you post the wiring diagram? I can´t see the resistors in the pictures, or the used voltage... jut to have an idea....
By the way, i suppose that the selected resistances values could  change the analog input, and the readed value, is it right?
Thanks!

[scratchr]

This only uses 2 leds, 2 transistors, and a 9v.

[madepablo]

Thanks scratchr,

I will try it!

Cheers, 

[Zorink]

You only need the resistors and power for lighting an LED, not for sensing. If you need help lighting an led you can use this calculator. When using LEDs as just sensors you only need an LED (see the very first pic with the LED hooked up to a multimeter).

[madepablo]

  Great!

The problem was that i didn´t see any resistance in the picture of step 5, neither for lighting or sense. This is why i asked... So thanks for the reply.

However, how did you connected a sensor led to to arduino?  i see something like this in the picture:

analog pin -------- (+)LED(-) ----------- GND pin
is it correct?

Thanks!

[madepablo]

  I reply myself:

It seems to be incorrect. So the inverse mode of the led should be connected in that way:

analog pin ---------- (-) LED (+) ------------ GND
                                          \\
                                      ---|<|----

Thanks!

[Jeters]

I wonder i you can build something using this method to be close to what http://www.youtube.com/watch?v=xahQ6BMvri4 can do, those are some wicked sensors

[Zorink]

You could make a very basic one, but I doubt you could get that kind of accuracy

[ReCreate]

How much Current do the LED's output under light?

[Zorink]

My multimeter read .000, so not a lot. I knew I forgot something, thanks. I'll put in step 4.

[AndyCSWu]

I connect 30 green LEDs in parallel. They generate 1.3V under a lamp. The current I get is 1.1 uA or 0.0011 mA. But the connection test of my multimeter doesn't beep when I test them.

[ReCreate]

Wow. Some mad efficiency we got here. :P

[ReCreate]

Hmm...That is Unusual.

[scratchr]

leds use silicon, also used in solar cells

[Jodex]

I always knew that LEDs can sense light, but I didn't have any other recources than my head : D

[A-Nony-Mus]

could you use a picaxe instead of an arduino?

[Zorink]

You can use anything, I included the Arduino program just as a proof of concept. The instructable is more about how LEDs can be used as light sensors for any application.

[matstermind]

so you put the + to + and - to -? instead of + to - and - to -.