22 August 2006
Mesopic Vision vision with fully adapted eyes at luminance conditions between those
of photopic and scotopic vision, that is, between about 3.4 and 0.034 cd/nr.
Metal Halide Lamp a high-intensity discharge (HID) lamp in which the major portion
of the light is produced by radiation of metal halides and their products of dissociation -
possibly in combination with metallic vapors such as mercury.
Orientation the relation of a building with respect to compass directions.
Overcast Sky one that has 100% cloud cover; the sun is not visible.
Overhang the distance between a vertical line passing through a specified point
(often the photometric center) of a luminaire and the curb or edge of a roadway.
PAR Lamp See pressed reflector lamp.
Partly Cloudy Sky a sky that has 30 to 70% cloud cover.
Pendant luminaire See suspended luminaire.
Peripheral Vision the seeing of objects displaced from the primary line of sight and
outside the central visual field.
Photometry the measurement of quantities associated with light.
Photopic Vision vision mediated essentially or exclusively by the cones. It is
generally associated with adaptation to a luminance of at least 3.4 cd/m.
Point-by-Point Method a method of lighting calculation, now called the point method.
Point Method a lighting design procedure for predetermining the illuminance at
various location in lighting installations by use of luminaire photometric data.
of radiation, whose dimensions are sufficiently small,
compared with the distance between the source and the irradiated surface, that these
dimensions can be neglected in calculations and measurements.
Pole (roadway lighting) a standard support generally used where overhead lighting
distribution circuits are employed.
Programmed Rapid Start a fluorescent starting method where the cathode is
preheated before the lamp is ignited. This softer ignition increases the number of starts
over the life of the lamp.
Quality of Lighting pertains to the distribution of luminance in a visual environment.
The term is used in a positive sense and implies that all luminances contribute favorably
to visual performance, visual comfort, ease of seeing, safety, and aesthetics for the
specific visual tasks involved.
Rapid-Start Fluorescent Lamp a fluorescent lamp designed for operation with a
ballast that provides a low-voltage winding for preheating the electrodes and initiating
the arc without a starting switch or the application of high voltage.
Rated Lamp Life the life value assigned to a particular type lamp. This is commonly a
statistically determined estimate of average or of median operational life.
Reflected Glare glare resulting from reflections
of high luminances