Cutoff classifications define the luminous intensity limits Cutoff classifications define the luminous intensity limits in two illumination zones that occur within the range of 80° to 180° above nadir.Īmerica (IESNA) that describes the light distribution of an outdoor cutoff classification - The classification system of the Illuminating Engineering Society of North America (IESNA) that describes the light distribution of anoutdoor luminiare. direct uplight - Light emitted upward by a luminaire. cutoff angle - The angle of light distribution from a luminaire, measured upward from nadir, between the vertical axis and the first line at which the bare source (lamp) is not visible. The source of uplight can be from a combination of direct uplight and reflected light. uplight - Light directed upward at greater than 90° above nadir. steradian (sr) - A unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere equal to the square of the sphere radius. spill light - Light that falls outside of the area intended to be lighted. sky glow - Brightening of the sky caused by outdoor lighting and natural atmospheric and celestial factors. This applies to all lateral angles around the luminaire. semicutoff luminaire - IESNA classification that describes a luminaire light distribution in which the candela per 1000 lamp lumens does not numerically exceed 50 (5%) at or above an angle of 90° above nadir, and 200 (20%) at or above a vertical angle of 80° above nadir. The overall light output of a lamp or luminaire. Luminous flux - Luminous radiant power, measured in lumens. 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. One footcandle equals 10.76 lux, although for convenience 10 lux commonly is used as the equivalent. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). illuminance - The amount of light (luminous flux) incident on a surface area. discomfort glare - The sensation of annoyance or even pain induced by overly bright sources.
disability glare - A type of glare that causes a loss of visibility from stray light being scattered within the eye. Ratings of initial light output provided by manufacturers express the total light output after 100 hours of operation.
A lamp's light output rating expresses the total amount of light emitted in all directions per unit time. lumen (lm) - A unit measurement of the rate at which a lamp produces light. Candela - The Systeme International d'Unities (SI) of luminous intensity.
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