Light and Color

Coloured gold alloys

“…The CIELAB method expresses the colour as three-dimensional co-ordinates: L*, a*, and b*, where L* is the luminance (brightness) (10). An L* value of 0 means that no light is reflected by the sample, and an L* value of 100 means that all incident light is reflected.…”

“…The spectrophotometer has a resolving power between five and ten times greater than the human eye (7,10). As the colour of a sample depends on the illuminant, the sample itself and the observer, the spectrophotometer uses an artificial light source that simulates natural light, an array of photodiodes, and the computer as the observer.…”

Light, Electromagnetic Spectrum

“…For example, white light can be produced by superimposing red, blue, and green lights in certain proportions. This was first demonstrated by Thomas Young [3] who used this experimental finding to theorize that the human eye contained three different types of color receptors, which is known as the trichromatic theory of human color vision.…”

“…The energy of a photon is given by E = hn where h is Planck's constant (6.62606 Â 10 À34 J s). Light can then be described as a stream of individual photons, each with a definite energy and that can interfere with each other like waves and diffract around corners [3]. The motion of these photons is controlled by these same set of Maxwell wave equations [2,3].…”

“…1). The British physicist James Clerk Maxwell [3] was the first to discover that these electric and magnetic waves always occurred together, i.e., were coupled, giving rise to the name, electromagnetic waves. It was also found that the lines of force of these electric and magnetic waves were always perpendicular to each other and perpendicular to the direction of wave propagation, i.e., transverse, never longitudinal.…”