Video Encyclopedia :Sodium flame looks dark when illuminated with sodium light.

Video Encyclopedia :A collection of fluorescent materials in black light.

A sinusoidal wave is printed on transparent material that can be wound up. As the radius of the windings gets bigger the waves add constructively (line up) or destructively (not lined up) like the De Broglie wavelengths in the Bohr orbit of the hydrogen atom.

Two diffraction gratings are oriented at right angles and a small lecture laser projects a pattern of dots similar to x-ray diffraction.