I

Image

The optical reproduction of an object, produced by a lens or mirror. A typical positive lens converges rays to form a “real” image that can be photographed. A negative lens spreads rays to form a “virtual” image that cannot be projected.

Incident light

A ray of light that falls on the surface of a lens or any other object. The “angle of incidence” is the angle made by the ray with a perpendicular to the surface.

Incoherence

Pertains to two or more waves that do not have a fixed phase relationship with respect to one another.

Infrared (IR) radiation

Invisible electromagnetic radiation with wavelengths that lie within the range of 0.70 to 1000 micrometers. This region is often broken up into IR-A, IR-B, and IR-C.

Integrated radiance

Product of the exposure duration and radiance. Also known as pulsed radiance.

Intensity

The magnitude of radiant energy.

Interferometer

A device that uses the principle of interference of electromagnetic waves for measurement purposes (e.g., to measure wavelength or temperature).

Intrabeam viewing

The viewing condition whereby the eye is exposed to all or part of a direct laser beam or a specular reflection.

Ion laser

A type of laser employing a very high discharge current, passing down a small bore to ionize a noble gas such as argon or krypton.

Ionizing radiation

Radiation commonly associated with X-ray or other high energy electro-magnetic radiation that will cause DNA damage with no direct, immediate thermal effect. Contrasts with non-ionizing radiation of lasers.

Iris diaphragm

Device that uses thin overlapping plates to change the diameter of a central opening and, therefore, to control the amount of light allowed through it. Enables users to adjust the diameter of a beam.

Irradiance (E)

Radiant flux (radiant power) per unit area incident upon a given surface. Units

Watts per square centimeter. (Sometimes referred to as power density, although not exactly correct.)

Irradiation

Exposure to radiant energy, such as heat, X-rays, or light.