An arc or flash lamp is a lamp that uses a luminous and heat emission of plasma bridge formed in a gap between two conductors or terminals when they are separated. A mercury arc lamp is a discharge arc lamp filled with mercury vapor at high pressure; it gives out a very bright UV and […]

A halogen lamp has an iodine-cycle tungsten incandescent lamp as the visible/near infra­red (360 nm to >1 pm) light source for spectrophotometry and phototherapy, and recently it has also been used in IR phototherapy. As it is gas-filled, the tungsten electrode can be heated up to 4000 K. At this temperature, the maximum spectra of […]

All bodies emit electromagnetic radiation in the wavelength spectral range and with intensities that correspond to their temperature. This is called heat radiation or blackbody radiation. Spontaneous and stimulated emission by atoms are the basis for the Planck curve (function), which gives the intensity radiated by a blackbody as a function of wavelength for a […]

3.1.2 Spontaneous and Stimulated Emission Light is emitted by atoms (molecules) of the light source material that can be a gas, a liquid, or a solid. Atoms can be in different excited states when electrons possess energy according to their position in relation to the nucleus of an atom. The closer the electron is to […]

Polarization of light is a state in which rays of light exhibit different properties in differ­ent directions. When the electric field vector of the EMR oscillates in a single, fixed plane all along the beam, the light is said to be linearly (plane) polarized; when the plane of the electric field rotates, the light is […]

Light refraction is the change in direction of a ray of light when passing obliquely from one medium into another in which the light speed is different. Light refraction is character­ized by the index of refraction-a number (n) indicating the speed of light in a given medium, as either the ratio of the speed of […]

Coherent light that is typically produced by lasers is light in which the electromagnetic waves maintain a fixed phase relationship over a period of time, and in which the phase relationship remains constant for various points in the plane that is perpendicular to the direction of propagation. Coherence length of a light source characterizes the […]

Evidently, light-tissue interaction depends on temporal parameters of the light, whether it is continuous wave (CW) or pulsed. A CW mode means that emitted waves are not intermittent or broken up into damped wave trains, but unless intentionally interrupted, follow one another without any interval of time between them. Pulsed light can be pro­duced as […]

In general, a light beam is a slender stream of light. Light is an electromagnetic wave. Electromagnetic waves can be characterized by wave fronts. A wave front is a surface where the electromagnetic field of light is oscillating in the same phase. In the geometric optics approximation, light can be presented as a family of […]