coating a piece of glass with an extremely thin clear coating (1/2-wavelength
thick), one can keep light from reflecting from the surface. The
thickness of the coating is designed so that the reflections from
the front and rear surfaces destructively interfere, cancelling
the reflection. The disks in this exhibit only have a central spot
coated so that the difference can be observed. The anti-reflection
coating also makes the glass more transparent (less loss).