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| ability of the eye to change the shape of the lens to focus on near or distant objects. |
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| ability of the eye to adjust to different levels of light by change in size of the pupil and by chemical changes in the photosensitive pigments of the retina |
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| electrical devise which supplies proper voltage, current and wave form conditions to start and operate discharge lamps |
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| subjective impression of light reaching the eye. Subjective brightness does not vary directly with measured brightness. |
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| unit of luminous intensity equal to one candle power |
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| unit of luminous intensity equal to one candle power |
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| relative evaluation of color temperature (warmth or coolness) of a light source. |
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| relationship between brightness (or color) of an object and that of its immediate surrounding. |
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| having the property of scattering incident light over a wide range of angles (eg, materials like plaster, wood, brick have diffuse surfaces) see also matte. |
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| efficacy of light sources |
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| Luminous efficientcy (in lm/W) expressed by lumen output of lamps per power input in watts. |
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| two aspects of visual perception which influence each other: a figure which has good contour and is separate from the background, and a background which is relatively homogeneous and not clearly patterned. |
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| quantity of light on one square foot of surface area one foot away from light source of one candela |
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| quantity of light reflected from or transmitted through an objet. (Matric measure is cd/m(squared) or nit |
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| harsh, uncomfortably bright light source or reflection which interferes with visual perception. Light from the wrong place at greater brightness than that to which eyes are adapted. |
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| quality of light (in fc or lx) which reaches a surface. To convert lux to footcandles, multiply by 0.09 |
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| complete light source unit, usually consisting of light-generating element (arc tube or filament), support hardware, enclosing envelope (bulb) and base. |
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| device to provide mechanical support and electrical connections (base pins and contacts)for fluorescent lamps |
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| shielding or diffusing portion of fixture which controls luminance and directs light. Also. transparent oval body behind iris which adjusts eye's focus on retina for near and distant vision. |
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| unit of light energy to specify light output of sources. It is the rate at which light falls on one square foot of surface area one foot from a source of one candela. |
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| complete lighting unit consisting of lamp(s) together with parts to position and protect lamp, direct light, and connect lamp to a power supply. |
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| angle equal to zero degrees and oriented vertically downward. |
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| measurement of quantities associated with light. Physical properties of a luminaire light output |
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| percentage of incidence of light on a surface which is re-radiated. It depends on angle of incidence and other factors. |
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| device used to redirect light from a souce |
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| divice used to redirect light. light rays change direction when passing obliquely from one medium (air) to another (glass or plastic) |
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| three-dimensional angle formed by three or more planes meeting at a point (eg. apex of cone, pyramid) Unit of measure for solid angle is steradian |
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| having the reflective properties of a mirror where the angle of incidence is equal to the angle of reflection. Example finishes are polished aluminum, stainless steel and tin. Angles are usually measured between light ray and line perpendicular to surface as shown below. |
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| details and objects that must be seen for performance of a given activity, including immediate background for details or objects |
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| how well a scene or object can be seen |
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| capacity to discriminate fine details of objects |
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