It’s important to know how the sensors work if you want the best pictures from your digital camera. The lens of the camera focuses the light on a plan behind the rear element. This is what is known as the film in a 35mm. In a digital camera the plan is silicon or a chip. Chips come in two forms which are Change-Copied Device (CCD) or Complementary Metal Oxide (CMOS).
On the chip, which is the sensor, are rays of light-sensitive spots called photosites. They are square in shape and lay out in rows and columns. With some sensors the active light collects areas for only 25% of the total area. If you are wondering how large the individual photosites are, the original Nikon D1x camera, there were only 11.8 microns square which were pretty large at the time. The Coolpix 990 was 3.45 microns square which are much smaller. Making these squares smaller was to have photo diode efficiencies increase to cover more area in taking pictures.
When light is not gathered by these chips in the rage of taking the photo, it is referred to as a Dark Current. This Current increases by temperature due to small gaps between the valence and conduction bands within the silicon. This can eventually cause the electrons to cross a gap where it does not belong. It takes very high temperature to increase the Dark Current to be visible. Most times it takes about 90 degrees for this to happen. On the flip side of it, if a camera gets too much light it can spill over from on photosite to another. This will eventually corrupt the file making the picture too light or not visible at all.
You may be surprise, but digital cameras see in black and white only! The job of the already busy sensor is to translate the colors to each square so that the image is duplicated as seen through the lens.