| Illuminance |
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The Illuminating Engineering Society of North America (IESNA) established seven illuminance categories based on descriptions of various visual tasks. These are the recommended levels of light for various tasks.
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| Common visual tasks |
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Visual performance is important. These tasks are found in commercial, industrial and residential applications. A desktop work space is normally lit to 30 to 50 footcandles. Recommended illuminance levels differ because of the characteristics of the visual task being illuminated. Higher levels are recommended for visual tasks with critical elements of low contrast or small size.
Category
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Space
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Illuminance
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D
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Performance of visual tasks of high contrast and large size
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30 footcandle (300 lux)
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E
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Performance of visual tasks of high contrast and small size, or visual tasks of low contrast and large size
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50 footcandle (500 lux)
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F
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Performance of visual tasks of low contrast and small size
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100 footcandle (1000 lux)
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| Orientation & simple visual |
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Visual performance is largely unimportant for this level of task. These tasks are found in public spaces where reading and visual inspection are only occasionally performed. Parking lots are normally lit to 5 footcandles. Higher levels are recommended for tasks where visual performance is occasionally important.
Category
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Space
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Illuminance
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A
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Public spaces
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3 footcandle (30 lux)
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B
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Simple orientation for short visits
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5 footcandle (50 lux)
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C
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Working spaces where simple visual tasks are performed
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10 footcandle (100 lux)
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| Special visual tasks |
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Visual performance is of critical importance. These tasks are very specialized, including those with very small or very low contrast critical elements. Medical surgical rooms are lit to 1000 footcandle. Recommended illuminance levels should be achieved with supplementary task lighting. Higher recommended levels are often achieved by moving the light source closer to the task.
Category
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Space
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Illuminance
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G
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Performance of visual tasks near threshold
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300 to 1000 footcandles
(3,000 to 10,000 lux)
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