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Lighting Units
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There are four basic concepts of practical light measurement: Luminous Flux, Luminous Intensity, Illuminance, Luminance. |
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The angle of direction of light incidence with the perpendicular to a plane |
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Illuminance is the quantity of light, or luminous flux, falling on unit area of a surface (Fig). It is designated by the symbol E. |
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Luminance is the concept for the luminous intensity emitted per unit of area of a surface in a specific direction. |
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Luminous flux is the concept for the total quantity of light emitted per second by a light source. It is designated by the symbol f. The unit is lumen (lm). |
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Luminous intensity is the concept for the concentration of light in a specific direction, radiated per second. It is designated by the symbol 1. |
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Relation between luminous intensity (I) and illuminance (E) |
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The luminous intensity in any direction of light source whose light distribution is uniform in all directions. |
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