I've got one of those heat lamps that produce a lot of infrared light and I've noticed the light sensor on my phone seems to be sensitive to that wavelength.

The lamp is 250 watts and aimed at the ceiling in a dimly lit room and it doesn't shine in any horizontal direction. However, the screen on my phone goes to very bright when ever the heat lamp is on. The phone is also about 15 feet away from the lamp and the screen is laying horizontal not toward the lamp. The part of the room where the phone is located is very dimly lit.

I've also got a CFL lamp tuned on in the same room, but the phone screen doesn't seem to light up unless the heat lamp is on. So I suspect the phone's light sensor is especially sensitive to infrared, but not sensitive to the light from a CFL bulb.

 

It seems likely that the phone's light sensor is it, but without knowing much about how they work I would expect the phone to dim with the heat lamp on, not get brighter. I guess that suggest that the sensor might trying to use spectral content somehow but its not working in this case.

 

Silicon photo sensors are very sensitive to IR (better than visible probably). The phone camera will have an IR filter fitted between the lens and the camera IC. Seems they have forgotten to put one over the light sensor used for the screen brightness control.

I have one of those wildlife cameras. The IR filter on the camera is automatically moved away for night vision.

 

hi,
Most mobile phone cameras will detect IR, useful when testing IR TV and other remote controls.
E