# illuminance

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## illuminance:

see photometryphotometry
, branch of physics dealing with the measurement of the intensity of a source of light, such as an electric lamp, and with the intensity of light such a source may cast on a surface area.
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## Illuminance

A term expressing the density of luminous flux incident on a surface. This word has been proposed by the Colorimetry Committee of the Optical Society of America to replace the term illumination. The definitions are the same. The symbol of illumination is E, and the equation is E = dF/dA, where A is the area of the illuminated surface and F is the luminous flux. See Luminous flux, Photometry

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

## Illuminance

Commonly called light level, illuminance refers to the light intensity arriving on a surface, measured in foot-candles (fc). It is the standard international unit that is used to measure the amount of light per unit of surface area, also known as lux (lx). Measurements of illuminance are used to select lighting fixtures and to evaluate a lighting design. The photometric data to be considered include the luminous-intensity distribution curve (LIDC), the coefficient of utilization (CU), and the light loss factor (LLF).
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Illuminance

(at a point of a surface), a unit of light, equal to the ratio of the luminous flux incident upon a small surface element ΔS containing the point being considered to the area of ΔS. Stated differently, illuminance is the surface density of the luminous flux. If the dimensions of the source of light are small in comparison with the distance l of the source from ΔS, then the illuminance E = I cos α/l2, where I is the luminous intensity of the source and α is the angle of incidence of the light upon ΔS, that is, the angle between the direction of the luminous flux and a line perpendicular to ΔS. Units of illuminance are the lux and the phot: 1 phot = 104 lux.

## illuminance

[ə′lü·mə·nəns]
(optics)
The density of the luminous flux on a surface. Also known as illumination; luminous flux density.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## illuminance

The density of luminous power, also called illumination. One lumen of luminous flux, uniformly incident on 1 square foot of area, produces an illuminance of 1 footcandle; in SI units, one lumen of luminous flux, uniformly incident on 1 square meter of area, produces an illuminance of 1 lux.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
Existing LED control systems focus on energy consumption by way of automatically turning lights on or off and adjusting illuminance by sensing the user's location without considering motions and behaviors.
Average illuminance results mad standard deviation of in-mold devices.
Linear light sources and luminaires that can be directly sequenced in installation are most suitable for creating even illuminance. Recessed illuminant positioning that prevents visibility of the luminaire from below is recommended for optimal glare protection.
The illuminance was measured at four points on the middle axis of the test room, and the backward raytracing software Radiance was used to simulate the interior space illuminance (Ward and Shakespeare 1998).
Several attempts have been made to describe mathematically the dependence of sine-wave contrast sensitivity on spatial frequency and illuminance simultaneously (e.g., Daly, 1993; Rovamo, Mustonen, & Nasanen, 1994).
The experimental luminous intensities were 0 (control), 350, 690, and 1380 cd per headlamp, corresponding to glare illuminance of, respectively, 0, 0.28, 0.55, and 1.1 lx at the observer's eye.
Thus, indirect lighting provides satisfactory illumination with a lower ambient illuminance level.
A direct reading provides a relatively accurate measurement of illuminance. Since the meter is color- and cosine-corrected, it mimics the color sensitivity of the human eye and can accurately measure light intensity from various directions.
In general, the security manager should provide an average horizontal illuminance - the amount of light that falls on a horizontal surface like a parking lot - of at least three foot-candles.
The various sensor configurations allow for measurement of luminous flux, illuminance, luminous intensity and luminance.
The number of possible activities is defined in the activity recognition block, and it must be related to the list of activities in the SRI (Standards of Recommended Illuminance) document, because the final decision depends on two components: value of light sensor (VLS) and SRI for the CA.

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