Diffraction at home

At home one evening I noticed a nice diffraction pattern caused by light from a neighbours light passing through a thin gauzy curtain which had a grid-like weave. A good topic for students - let them explain the effect.
Here is a photo at the right. You can see the coloured fringes speading out from the light in the vertical and horizontal directions, four sets in all. The bottom one is clearest. They are clearer in reality than they are in the photo.