Why don’t we see interface in situations where there are two sources of light? Watch
Is it because the two lights cancel out the interface? I have no idea.
I hope you don't find it too frustrating to get a hint rather than the answer - the key issue is that the light sources are 'incoherent' - if that doesn't ring a bell in itself, you should be able to look up the keyword in the context of interference in your textbooks or online.