Light is ultra-high frequency electromagnetic wave that travels at 3 × 108 m/s.
Light amplitude is measured in foot-candles (fc) or lux (lx). The wavelength
of visible light is from 4 to 7 × 10−7 m. Longer wavelengths of electromagnetic
waves are termed infrared and shorter wavelengths, ultraviolet. Light
wavelengths are sometimes expressed in terms of angstroms (Å) where 1 Å =
1 × 10−10 m.