I was just looking out of window at night when i saw a tower with a light on top. It had a red light . When i looked at it through my curtains with net on i saw an interference fringe , one is the main light itself and band of lights on either side of it(like interference of waves). Although there was no screen why did i see it . Did the air acted like screen so i saw it ? Was it because nets of curtain acted like slits , which produced that pattern ?Or is it some other simple diffraction or anything of light . I dont think its because of other simple reason because interference pattern was clear . Any process that can explain this phenomenon?
What you are seeing is an interference pattern, similar to double slits or diffraction gratings. You can confirm this comparing the light pattern when you are looking straight through the curtain (when the curtain is perpendicular to the line from you to the light) and when the curtain is at an angle. Angling the curtain makes the threads appear closer together, so the interference fringes will spread out more.
The pattern is easier to see when the source in monochromatic (LEDs and the like).