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?
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1Related: Whats the use case of proximity sensor? Also see: Wikipedia: Proximity sensor and Proximity Sensor on Android Gingerbread . The latter article gives you a close insight in proximity sensors and how they're used on Android devices. – Izzy Dec 08 '14 at 16:57
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Thank you for your answer. The website you linked shows that while in general a proximity sensor can be implemented with various technologies such as electrical (inductive, capacitive), optical (IR, laser), magnetic, and sonar, the cheapest solution is the one implemented in mobile phones and makes use of optical (light) sensors. Thanks. – John Sonderson Dec 08 '14 at 17:25
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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.
csapdani
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Thank you for your answer. However, I think that the proximity sensor is not useless at night, and can still use light to detect proximity. At night light is reflected from the screen against the user's face and back to the proximity sensor, which by comparing light entering the two separate openings somehow can determine the amount of proximity of the deive to the user's face. Correct me if I'm wrong. Perhaps not all proximity sensors on all devices work the same way. – John Sonderson Dec 08 '14 at 17:09
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@JohnSonderson That still wouldn't work, because the screen turns off when you trigger the proximity sensor. It would never know when to turn the screen back on again. Typically there's an infrared light next to the sensor, and it measures the reflection of that light. That's why the proximity sensor often has two adjacent apertures. – Dan Hulme Dec 08 '14 at 18:05
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OK. I tried locking myself in the closet in complete darkness, called my mobile phone from my cordless home phone, answered my mobile phone, and placed it near my ear (phone went blank), then away from my ear (phone lit up again). So you are right here. But what I noticed is that as soon as I answer my phone the proximity sensor activates itself by displaying a red light in the LED on the left while no light is displayed in the LED on the right. – John Sonderson Dec 08 '14 at 19:12
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When I bring my finger within less than a centimeter of this light it blinks and the screen turns off, then when I move my finger away from it the light blinks again and the screen turns on. So, perhaps my theory was wrong, but it works pretty well despite the fact I still haven't figured out how it works. Comments welcome. Thanks. – John Sonderson Dec 08 '14 at 19:13
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@DanHulme, I think it is not the light of the screen which bounces off the user's face and activates the proximity sensor, but the intensity of the red light from the proximity sensor (or perhaps the infrared component of this light which is more likely), that bounces off the user's face and creates a reading on the proximity sensor itself. Regards. – John Sonderson Dec 08 '14 at 19:59
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Feel free to correct me if I'm wrong, but as I understand it, the proximity sensor is what's used in call to stop your face from providing unwanted touch input. It usually glows red while activated and emits infrared.
The light sensor is what is used to measure light levels for things like adaptive brightness.
1990clb
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I just checked the Samsung Galaxy SIII Manual which can be downloaded form this site. According to the manual, at least on this mobile phone, the proximity and light sensor are the same physical device. This device is used as a light sensor to increase the screen brightness at night and decrease it during the day, and as a proximity sensor to make sure the screen turns blank when the phone is placed next to the earpiece when receiving a phone call to ensure non of the buttons get accidentally pressed against the user's face.
Despite the two sensors use the same hardware device, two separate software algorithms are used to make it behave as two separate sensors.
Other manuals such as the one for the Samsung Galaxy S Plus which can be downloaded here list the light sensor and the proximity sensor separately, although the appearance of these is always the two small adjacent circles that let light into the hardware behind those two light entrances.
John Sonderson
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