Nature of light
Light is transverse, electromagnetic wave motion that can be detected with the human eye.
Light is produced by one of two methods:
- Incandescence is the emission of light from "hot" matter (temperature T ≳ 800 Kelvins),
- Luminescence is the emission of light when excited electrons fall to lower energy levels
Like all electromagnetic waves, light can travel through vacuum. The speed of light in vacuum is represented by the letter c from the Latin celeritas — swiftness. The speed of light in vacuum is fixed at 299,792,458 m/s and this fundamental quantity is related, for instance, to the current definition of the meter. The speed of light in a medium is always slower than the speed of light in vacuum. The speed of light depends upon the medium through which it travels. The speed of anything with a mass is always less than the speed of light in vacuum.
Light and colours
The amplitude of a light wave is related to its intensity. Intensity is the absolute measure of a light wave's power density. Brightness is the relative intensity as perceived by a typical human eye.
The frequency of a light wave is related to its color. Monochromatic light is described by only one frequency. Laser light is effectively monochromatic. There are six colors each associated with a band of monochromatic light. In order of increasing frequency they are red, orange, yellow, green, blue, and violet. Polychromatic light is described by many different frequencies. Nearly every light source is polychromatic. For example, white light is polychromatic.
Adapted from //physics.info/light/