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GLOSSARY
Opposite arrangement
A road-lighting arrangement in which the luminaires are placed on either
side of the carriage way(s) opposite to one another.
Optical light
output ratio
Of a luminaire. The ratio of the total flux of the luminaire, measured
under specified practical conditions, to the sum of the individual luminous
fluxes of the lamps when inside the luminaire.
Note
For luminaires using incandescent lamps only, the optical light output
ratio and the light output ratio are in practice the same.
Optical radiation
Electromagnetic radiation at wavelengths between the region of transition
to Xrays (l» 1nm) and the region of transition to radio waves (l» 1 mm).
Photometry
Measurement of quantities referring to radiation as evaluated according
to a given luminous efficiency function, e.g. V(l) or V'(l).
Power factor
In an electric circuit. The ratio of the power in watts to the product
of the r. m. s. values of voltage and current. For sinusoidal waveforms,
it is equal to the cosine of the angle of phase difference between voltage
and current.
Preheat (or
rapid-start) lamp
Hot cathode lamp designed to start with preheating of the electrodes.
Radiation
1. Emission or transfer of energy in the form of electromagnetic waves
or particles.
2. These electromagnetic waves or particles
Radiant power,
( Fe, F)/ Radiant Flux
Power emitted, transferred, or received in the form of radiation. Unit:
watt, W
Rainproof
luminaire
Luminaire so constructed as to withstand the penetration of rain, and
for use out of doors.
Recessed luminaire
Luminaire mounted above the ceiling or behind a wall or other surface
so that any visible projection is insignificant.
Reference surface
Surface on which illuminance is measured or specified.
Reflection
Return of
radiation by a surface or medium without change of frequency of its monochromatic
components.
Reflector
Device in which the phenomenon of reflection is used to alter the spatial
distribution of the luminous flux from a source.
Reflector lamp
Lamp in which part of the bulb is coated with a reflecting material, either
diffuse or specular, so as to control the light.
Regular (or
specular) reflection
Reflection, without diffusion, in accordance with the laws of geometrical
optics; as in a mirror.
Retina
Membrane at the back of the eye, which is sensitive to light stimuli and
containing photoreceptors (cones and rods) and nerve cells that transmit
the stimulation to the optic nerve.
Room index
(K)
Code number, representative of the geometry of a room, used in calculation
of the utilization factor or the utilance.
Note 1
Unless otherwise indicated, the room index is given by the formula K =
(l x b)/h(l + b) where: l is the length of the room, b is the width and
h is the distance of the luminaires above the working plane.
Note 2
The 'ceiling cavity index' is calculated from the same formula except
that h is the distance from ceiling to luminaires.
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