What are the conditions for sustained interference of light?

The conditions to produce Interference

1. The two interfering sources must be coherent.
2. The two interfering waves must have the same amplitude or nearly equal amplitude.
3. The waves should have a certain path difference.
4. The light source used must be monochromatic.
5. The two sources must be very close to each other.
6. The two sources should be very narrow.
7. For consecutive interference, path difference = nλ, and for destructive interference, path difference = \(\left(n+\frac12\right)\lambda\), where n is the integer and λ is the wavelength of light is used.