In photometry, illuminance is the total luminous flux incident on a surface, per unit area.[1] It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception.[2] Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance.[3][4]
In SI units illuminance is measured in lux (lx), or equivalently in lumens per square metre (lm·m−2).[2] Luminous exitance is measured in lm·m−2 only, not lux.[4] In the CGS system, the unit of illuminance is the phot, which is equal to 10000 lux. The foot-candle is a non-metric unit of illuminance that is used in photography.[5]
Illuminance was formerly often called brightness, but this leads to confusion with other uses of the word, such as to mean luminance. "Brightness" should never be used for quantitative description, but only for nonquantitative references to physiological sensations and perceptions of light.
The human eye is capable of seeing somewhat more than a 2 trillion-fold range. The presence of white objects is somewhat discernible under starlight, at 5×10−5 lux, while at the bright end, it is possible to read large text at 108 lux, or about 1000 times that of direct sunlight, although this can be very uncomfortable and cause long-lasting afterimages.[citation needed]
^"Illuminance, 17-21-060". CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition. CIE - International Commission on Illumination. 2020. Retrieved 20 April 2023.
In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates...
The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per...
The Kruithof curve describes a region of illuminance levels and color temperatures that are often viewed as comfortable or pleasing to an observer. The...
this area, illuminance at point r on d A , E v ( r ) = ∑ i | a ^ ⋅ ( r − r i ) | | r − r i | 3 I i . {\displaystyle {\text{illuminance at point }}\mathbf...
seconds) E is the image-plane illuminance (lux or lumens/m²) t is the exposure time ("shutter speed") (seconds) The illuminance E is controlled by the f-number...
The solar constant (GSC) measures the amount of energy received by a given area one astronomical unit away from the Sun. More specifically, it is a flux...
luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills...
slightly revised definition of illuminance, measurements with a hemispherical receptor indicate "effective scene illuminance." It is commonly stated that...
explanation of why it is not exactly half, see here). However, the outdoor illuminance can vary from 120,000 lux for direct sunlight at noon, which may cause...
Eo) x 100% where, Ei = illuminance due to daylight at a point on the indoors working plane, Eo = simultaneous outdoor illuminance on a horizontal plane...
task lighting refers to increasing illuminance to better accomplish a specific activity. However, the illuminance level is not the only factor governing...
approximately 0.935338. The solar illuminance constant (Esc), is equal to 128×103 lux. The direct normal illuminance (Edn), corrected for the attenuating...
Building Design engineers and architects to predict luminance and/or illuminance within buildings using standardised sun and sky condition climate data...
lighting applications that require minimal glare and uniform general illuminance levels. Uplighting (indirect) uses a diffuse surface to reflect light...
Nitric oxide (NO) Nitrogen dioxide (NO2) Nox (unit) (nx), a unit of illuminance Nox (platform), a piece of the software-defined networking ecosystem...
spectrum, and absorption spectrum. Starlight illuminance coincides with the human eye's minimum illuminance (~0.1 mlx) while moonlight coincides with the...
visible light measured by a luxmeter at a certain point. Central illuminance (Ec) Illuminance (measured in lux) at 1m distance from the light emitting surface...
information entropy, luminous intensity, luminance, luminous flux, illuminance, radiation. Notes: See Weight for detail of mass/weight distinction and...
which may vary with time and position." The wide spectrum of possible illuminances in the natural environment and the limited ability of the human eye to...
algorithm is integrating over all the illuminance arriving to a single point on the surface of an object. This illuminance is then reduced by a surface reflectance...
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