ABSTRACT
Radiation waves can be characterized as being electromagnetic since they are composed of two orthogonal oscillatory waves carrying electric and magnetic components. When electromagnetic radiation interacts with matter, it exhibits particle-like behavior since its interactions with molecules are restricted to discrete packets of energy called photons. The requirement that energy be transferred only through the absorption of specific photons is dictated by quantum mechanics, and this principle explains why only certain wavelengths of light can induce any given photo-biologic skin reaction, even though all light sources serve as sources of energy. For humans the correct balance of light exposure necessary for health maintenance varies dramatically between individuals based on skin phenotype, presence of pathologic photosensitivity, and genetic factors. In an incandescent light bulb, electric current is passed through a thin tungsten filament, which generates heat and light due to electrical resistance.
