There is an article in the new Nuts & Volts that describes using LEDs as photometers. It is based on a Forrest Mims article that states that the LED will produce a current if the wavelength of light incident on it is in the narrow band that the LED emits at. I made two photometers, one with a red LED and one with a green LED. When I shine red light on the green LED I get no current, but when I shine green light on the red LED I do get current, inconsistent with Forrest Mims.
I would expect that if the incident photons have an energy equal to or greater than the detector LED band gap I will get electrons getting kicked across and giving a current, consistent with my observation. Doing a Google search, I find a lot of people post that the detector response is in a narrow band, and others, one from Analog Devices, saying the detector LED will respond to light at wavelengths equal to or less than the wavelength it emits at.
Do you guys have any comments on this. I have to believe my observations and I trust Analog Devices to be a reputable source. All I know about Forrest Mims is he seems to be quite the self promoter.