If 1- Optically speaking, an image point (or pixel) is a light interference pattern

2- interference patterns require phase coherence


3- the source of the image point must emit coherent light


4- common image points (or pixel) represent a source larger than one atom


5- the coherent light must be emmited by a source bigger than one atom

My first question is do you find errors in the above logic ?

Then if the above is true, then let's imagine we take the picture of a bright light bulb in a dark room, how can you explain that the filament emits coherent light in areas big enough to create image points?

Furthermore let's imagine the picture taken from an object lighted by several bulbs, how could such object reflect light coherent enough for the image to be formed ?


2 Answers 2


1- Optically speaking, an image point (or pixel) is a light interference pattern

This is not true. Images are a phenomenon in ray optics.

  • $\begingroup$ no, ray optics are just an approximation of wave optics. here's a good lecture about this: youtube.com/watch?v=sTa-Hn_eisw $\endgroup$ May 3, 2019 at 21:49
  • $\begingroup$ @ManudeHanoi: Your comment is not in contradiction with my answer. $\endgroup$
    – user4552
    May 3, 2019 at 23:02
  • $\begingroup$ Perhaps you meant that images are strictly a ray phenomenon optic and not a wave optic phenomenon. Which you didnt clearly specify. But if you did, I would deny that too $\endgroup$ May 4, 2019 at 2:20

from wiki:

In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference.

My question resulted from a misunderstanding of the "coherent" meaning. Light can change frequency, shape, phase and still be spacially coherent. In the case considered: a point source is always spacially coherent with itself.

Unlike lasers, there is little to no temporal coherence (no change in phase & frequency over a period of time) in regular light point source .

In usual imaging conditions (human eye, regular cameras) the ability to form a static interference pattern and therefore an image depends on spacial coherence not temporal coherence (a change in frequency will alter the pattern but it has to be big to be noticeable)


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