# 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

## 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).

## 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.

## 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.
References in periodicals archive ?
At each bin of the indoor illuminance on the ceiling, the number of occupied time steps when occupants turned on lights has been divided by the total occupied time steps at that bin when lights were off.
RECOMMENDED ILLUMINANCE RANGE FOR THE DIFFERENT TYPES OF ACTIVITY.
The effects of lighting conditions on productivity have been published in the several studies the earliest studies indicated that lighting conditions can improve performance by providing adequate illuminance for the visual tasks.
For a further characterization of illuminants and light sources, the light colour of fluorescent lamps is compared to the light colour and illuminance of light bulbs.
When Illuminance E is below 500 lux, the light is turned on; otherwise, it is turned off.
During illuminance characterization, results were gathered from all screen printed and basic airbrushed devices but only three out of the five in-mold made parts illuminated over the whole area of the EL device; and of those three, all failed at the highest operating conditions (the values recorded during the test were the highest illuminance achieved before failure).
Since walls are located in the main field of vision and illuminated walls contribute to a subjective sense of brightness, this type of lighting has particularly high relevance for perception-oriented and efficient illumination of rooms, although lighting guidelines are often limited to specifying horizontal illuminance values [Cuttle, 2010; Krautter and Schielke, 2009; Loe and Rowlands, 1996].
9 In science, illumination and illuminance means the intensity of what on a surface?
In addition, the Area Lighter's modular optical ring design produces superior vertical illuminance, efficiently delivering the required amount of light without wasteful or irritating light spill into neighbouring areas.
Littlefair (2001) provided a design tool that calculates where global horizontal radiation and illuminance reach the buildings envelopes.

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