Lighting Technology, 2nd Edition

3

Theory of light

 

3.1 Electromagnetic spectrum

The narrow band of electromagnetic radiation which lies between UV and infrared with wavelengths from 0.0004 mm (400 nm) to 0.0007 mm (700 nm) is detectable by the human eye and is known as light (see Figure 3.1).

Figure 3.1 Electromagnetic spectrum

When an object is heated it radiates energy in the form of electromagnetic waves. These waves go from the radio wave end of the electromagnetic spectrum through the infrared, the visible, the UV, X-ray and gamma ray. Ultraviolet is invisible to human beings, but unfortunately, in significant amounts is extremely harmful. Infrared is also invisible ...