LED as sensor

Using Arduino Sensors
1

Hi there

I am considering using LEDs as light sensors. I have seen this done in several cases, however, I do not know what frequency they respond to.

Does anyone know if I can use a red LED to specifically measure red light intensity? Could I use multiple coloured LEDs for colour detection?

Does anyone have any experience on this matter, or can anyone point me to a good source on the topic?

Thanks

p.

2

Frankly, it would be easier to use a sensor designed for this purpose (color sensing). Check out the TAOS TCS3210D-TR for example.

--
The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

3

Using an LED as a light sensor works but the method I used had two drawbacks:

  1. It's slow because you use the LED as a capacitor and wait for it to discharge
  2. it uses two data pins per LED.

If your LED's have tinted plastic lenses they will act as filters to limit the sensitivity to other colors. For LED's with clear lenses I have no idea if the color of LED has any significant effect on the color sensitivity of the LED.

4

When using an LED as a sensor, my experience has been that the LED will only respond to light from the same wavelength, and it actually has to be fairly close, so matched LEDs work best. A red LED can be triggered by another red LED of the same wavelength or reflections from its own light, but not from an LED of another wavelength. This causes problems if the LED acting as a sensor is in direct sunlight as it will produce sporadic results as the sun is full spectrum. Also as pointed out above steer clear from LEDs with a colored diffuser, you will want a clear LED.

Hope that helps,