Filter
Optic element that can totally or partially select the wave lengths of a light source
spectrum. In case of a total selection (net cut of the wave lengths between certain
values), it is called a bandpass filter.
Flood
Term to identify a 2 ½ theta opening between 15 and 20° in a projector.
Fluorescent source
Discharge lamp of the low pressure mercury type in which most of the light is emitted
by a layer of fluorescent material excited by the ultraviolet radiation of the discharge.
Fresnel lens
Element allowing construction of large optics and small focal distance without the
obstruction, the thickness and the weight of the material used to produce a spheric
conventional lens of equivalent diottric power. The result is obtained dividing the
spheric lens into a series of concentric circular sections, called Fresnel rings. For each
zone the thickness of the lens is limited, while the continuous curve is transformed
into a series of surfaces of non-continuous with the same curvature.
G
General Lighting
Essentially uniform lighting of an area or a volume that does not take into account
specific local needs.
Glare
Visual condition in which there is discomfort or reduction of vision, caused by an
unsuitable distribution or degree of brightness or too much contrast in space
and time.
Goniophotometer
Instrument for the measurement of photometric magnitudes, for measuring the
angular distribution of a magnitude of brightness emitted by a light source, a lighting
fixture, a medium or a surface.
H
Halogen source
Lamp containing a tungsten filament and a small amount of one or more halogen
gases for the purposes of cyclic regeneration of the filament.
Hybrid optic
Optical system in which both mirrors and lenses are used. More generally, both reflec-
tive and refractive elements are employed.
