conditions for interference

1. The waves emitted from the two or more light sources are  coherent.  

 2. The distance between the two sources should be small.

3. The distance between the two sources and the screen should be large.

4. The background of the screen should be dark.

5.The amplitudes of the light waves should be equal or nearly equal.

6. The sources should be narrow.

7. The sources should be monochromatic.

8.The waves emitted from the two or more light sources have same amplitude,wavelength and frequency.