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Why would any smartphone (e.g. the Samsung Galaxy S5) need an ambient light sensor if it already has a front-facing camera?

Surely it requires time and money for the engineers to design an ambient light sensors into a phone's motherboard.

When light sensing is needed (e.g. for automatic screen-brightness adjustment), why doesn't the phone simply do the following every ten or twenty seconds?:

  • Power up the front-facing camera.
  • Capture an ultra-low-resolution photo.
  • Analyze it in order to see how light or dark the room is.

This could all be done automatically by the phone's operating system.

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    \$\begingroup\$ You want to perform 3 expensive operations in order to save 25 cents? \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 19 '15 at 18:19
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    \$\begingroup\$ @IgnacioVazquez-Abrams: surely nobody has ever moved a problem to software to cut down on a BOM. That's why 555 circuits are still so prevalent in modern designs and microcontrollers haven't really caught on :) \$\endgroup\$ – Bryan Boettcher Feb 19 '15 at 18:26
  • \$\begingroup\$ Why are you considering the development cost to integrate the sensor, but not the cost to do all the analysis of the image? software isn't free to make. \$\endgroup\$ – Gorloth Feb 19 '15 at 18:27
  • \$\begingroup\$ @insta: Phones have moved from NiCad to NiMH to Li-ion and they still don't stay charged long enough. \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 19 '15 at 18:37
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    \$\begingroup\$ @SpehroPefhany: In America, you look at smartphone. In communist country, smartphone looks at you! :) \$\endgroup\$ – unforgettableid Feb 19 '15 at 19:12
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The answer is simply that keying the camera uses more power and takes longer. Solve that problem, and make cmos cameras cheaper than light sensors, the light sensor would go away.

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  • \$\begingroup\$ Thank you for the quick and good answer. +1 and accepted. What does "keying" mean? \$\endgroup\$ – unforgettableid Feb 19 '15 at 18:56
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    \$\begingroup\$ The sensor has to be started up and interfaced with the systems bus. You know, like keying a microphone - starting it up. \$\endgroup\$ – Sean Boddy Feb 19 '15 at 18:59

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