LED bulbs and interference fringes in soap bubbles

We've probably all seen the rainbows you get as soap bubbles thin out to the point where their thickness is only a few multiples of the wavelengths of light. They're quite pretty. Light reflected from the back of the film and light reflected from the front interferes, and when the distance is right some colors can cancel or can be made brighter.

Since an LED bulb only uses a few frequencies/wavelengths, the resulting "rainbow" is much sharper and more dramatic. Tilt a ring or hoop with a soap film across it so that it reflects the light from an LED bulb, and watch as it thins out. Near the top you'll see several narrow bands of "rainbows", and as the bubble thins they'll get wider.