Question

Why are two electric bulbs not coherent?

Answer 1

Two electric bulbs are not coherent:

1. When the phase difference between two waves is constant then they are coherent.
2. Two electric bulbs' light can not be coherent, and the direction and time of the emission of photons by the two electric bulbs can not be controlled.
3. Two light bulb has different phase and frequency.

The diagram of the coherent light source is given below;