PIXEL SIZE: NOISE LEVELS & DYNAMIC RANGE
Larger sensors generally also have larger pixels (although this is not always the case), which give them the potential to produce lower image noise and have a higher dynamic range. Dynamic range describes the range of tones which a sensor can capture below when a pixel becomes completely white, but yet above when texture is indiscernible from background noise (near black). Since larger pixels have a greater volume and thus a greater range of photon capacity these generally have a higher dynamic range.
digital sensor pixels
Note: cavities shown without color filters present
Further, larger pixels receive a greater flux of photons during a given exposure time (at the same f-stop), so their light signal is much stronger. For a given amount of background noise, this produces a higher signal to noise ratio and thus a smoother looking photo.
Larger Pixels (with a Larger Sensor)
Smaller Pixels (with a Smaller Sensor)
This is not always the case however, because the amount of background noise also depends on sensor manufacturing process and how efficiently the camera extracts tonal information from each pixel (without introducing additional noise). In general though, the above trend holds true. Another aspect to consider is that even if two sensors have the same apparent noise when viewed at 100%, the sensor with the higher pixel count will produce a cleaner looking final print. This is because the noise gets enlarged less for the higher pixel count sensor (for a given print size), therefore this noise has a higher frequency and thus appears finer grained.
