G
gas-filled
lamp
an incandescent lamp in which the filament operates in a bulb filled with one
or more inert gases.
gaseous
discharge the emission of light from gas atoms excited by an
electric current.
general
color rendering index, Ra Measure of the average shift of eight
standardized colors chosen to be of intermediate saturation and spread
throughout the range of hues. If the color rendering index is not qualified as
to the color samples used, Ra is assumed.
general
diffuse lighting lighting involving luminaires that distribute 40
to 60% of the emitted light downward and the balance upward, sometimes with a
strong component at 90° (horizontal). See directindirect lighting.
general
lighting designed to provide a substantially uniform level of
illuminance throughout an area, exclusive of any provision for special local
requirements. See ceiling area lighting,
direct lighting, direct-indirect lighting, general diffuse lighting, indirect
lighting, localized general lighting, semidirect lighting, and semi-indirect
lighting.
general-purpose
floodlight (GP) a weatherproof unit so constructed that the
housing forms the reflecting surface. The assembly is enclosed by a cover
glass.
glare the
sensation produced by luminances within the visual field that are sufficiently
greater than the luminance to which the eyes are adapted, which causes
annoyance, discomfort, or loss in visual performance and visibility. See
blinding glare, direct glare, disability glare, and discomfort glare.
Note The magnitude of the
sensation of glare depends on such factors as the size, position, and luminance
of a source; the number of sources; and the luminance to which the eyes are
adapted.
globe
a transparent or diffusing enclosure intended to protect a
lamp, to diffuse and redirect its light, or to change the color of the
light.
glossometer an
instrument for measuring gloss as a function of the directionally selective
reflecting properties of a material in angles near to and including the
direction giving specular reflection.
glow
discharge an electric discharge characterized by a low,
approximately constant current density at the cathode (on the order of 10
µA/mm2) at low cathode temperature and a high voltage drop (typically 50 V or
more). Secondary emission from the cathode is much greater than the thermionic
emission.
goniophotometer a
photometer for measuring the directional light distribution characteristics of
sources, luminaires, media, and surfaces.
graybody a
temperature radiator whose spectral emissivity is less than unity and the same
at all wavelengths.
ground-area
open floodlight (O) a unit providing a weatherproof
enclosure for the lamp socket and housing. No cover glass is required.
ground-area
open floodlight with reflector insert (OI) a weatherproof
unit so constructed that the housing forms only part of the reflecting surface.
An auxiliary reflector is used to modify the distribution of light. No cover
glass is required.
ground light visible radiation from the sun and sky
reflected by surfaces below the plane of the horizon.
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