Radiation It was discovered that normal objects actually emit radiation, or "glow". At room temperatures, this light that is emitted is usually not visible. But as has been seen on television, the use of night goggles permits the wearer to see infrared light. Warmer objects (like human bodies) appear to glow brighter. This is called black body radiation.

When a wave is confined to a specific place, only certain wavelengths--those that can fit the space available--are allowed. These allowed waves reflect from the boundaries of the space and the reflection reinforces the original wave (constructive interference). All other wavelengths cancel each other out by destructive interference.

As the wave frequency is increased, the wavelength decreases.