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I have read the basics of how a digital camera works. As much as I have understood, the digital cameras have a device called a CCD on which photons coming from the lens are incident. The CCD then creates photoelectricity by gaining energy from the photons.

But then the cameras should not work at night (or other bad lighting conditions) since the photoelectric effect can only be seen for photons having higher than threshold energy. The only way I can think it works is that the CCD has a very low threshold. But that itself would require heavy quantizers for good lighting conditions (too much input) and would also be ultra sensitive to heat. I really think I am missing some key thing here. So how do digital cameras work?

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possibly helpful: – Carl Witthoft Jan 20 at 15:23
light intensity is like rate of fire, photon energy is like calibre – jk. Jan 20 at 17:46
you seem to assume that the same settings are used for low and high intensities. Adding noise or filtering the input are common in common usage. Scientists use preferably cooled cameras ( with bolometers ) , mainly efficient for a targeted frequency, which shows the variety of implementations. If not correct, please say why. – igael Jan 20 at 18:29
up vote 16 down vote accepted

The problem is that you are confusing light intensity with energy of a single photon. The photoelectric effect requires a certain energy per photon to work. But low light intensity just means fewer photons come - you can actually see the grain if the conditions are too dark: every pixel can get ~10 photons or less... and yet still, each photon that comes has the same energy (assuming it has the same wavelength). Well... you get a range of energies in the visible light spectrum, but all must be above threshold for the CCD to work (which they are by design of the sensor).

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