What is the difference between a proximity sensor and a light sensor? I've run across the specifications for this Android device, the HTC One V. On the PhoneArena site, the specs have it that the phone has both a proximity sensor and a light sensor. I thought a proximity sensor uses light to detect proximity. What is the difference between these two?
If the proximity sensor worked by simply measuring received light, it would be useless at night :) There are various methods this sensor can work, but the main idea is to decide if the phone is being held up at a person's ear. This is a yes or no question so the sensor doesn't have to be able to measure the distance, there just has to be a designated treshold, which, when crossed, triggers the output value from 0 to 1 (and thus, it turns off the screen).

The light sensor, however, needs to measure the brightness the phone is exposed to, usually to be able to adjust the screen's brightness. This way, for example, it can turn up the brightness in sunlight and reduce it at night.