I did the following -- I took a small pocket laser (cost USD5) and covered the aperture with a piece of paper and taped the paper to the laser. With a small pin I poked two holes side by side into the paper over the aperture. Then I taped the power button down so it stayed on, and positioned it to point at a wall about 8 feet away in a pitch black room.
When I looked at the 1/4th inch spot on the wall, there were many bands of bright and dark. I then hooked the laser up to a 6 volt lantern battery and proceeded to repeat the experiment. This time the intereference patterns were a total of 1 inch across and each band was atleast 1 or 2 16ths of an inch thick, and it was bright enough to be seen without turning off any lights.
Try it! Its great!
