25 - Lighting

Abstract

Light is a form of electromagnetic radiation similar in nature and behavior to radio waves at one end of the frequency spectrum and X-rays at the other. The human eye is more sensitive to frequencies in the middle of the spectrum than those at the ends. The average illumination on a surface will diminish as the square of its distance from the source. This is known as the inverse square law and is common to all forms of radiation. Light is reflected from a polished surface at the same angle as it strikes it. A matt surface will reflect it in a number of directions and a semi-matt surface will behave in a manner between the two. Refraction occurs when light passes through a surface between two media. The ray of light is bent and this property is used in the manufacture of lenses and prisms. The majority of light sources emit light in all directions. The function of most luminaires is to redirect the light of a bare electric lamp in a preferred direction with the minimum of loss, to reduce glare from the light source, to be acceptable in appearance, and, in some cases, make a contribution to the decor of the surroundings.