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.
Infrared
Abbreviated IR. The region of the electromagnetic spectrum between the long-wavelength extreme of the visible spectrum (~700nm) and the shortest microwaves (~1mm).
[box]Note: the International Commission on Illumination (CIE) recommended the following division:
IR-A: 700nm – 1400nm
IR-B: 1400nm – 3000nm
IR-C: 3000nm – 1mm[/box]
Intensity
The magnitude of radiant energy (light) per unit, such as time or reflecting surface.
Intrabeam Viewing
The viewing condition within which the eye is exposed to all or part of a laser beam.