As visual perception varies logarithmically, it is helpful to have an appreciation of both illuminance and luminance by orders of magnitude.
Illuminance To help compare different orders of magnitude, the following list describes various source in lux, which is a lumen per square metre.
Factor(lux) Multiple Value Item00 lux0 luxAbsolute darkness 10−4 100 microlux 100 microlux Starlight overcast moonless night sky 140 microlux Venus at brightest 200 microlux Starlight clear moonless night sky excluding airglow 10−3 1 millilux 2 millilux Starlight clear moonless night sky including airglow 10−2 1 centilux 1 centilux Quarter Moon 10−1 1 decilux 2.5 decilux Full Moon on a clear nightPaul Schlyter, Radiometry and photometry in astronomy FAQ (2006) 100 1 lux < 1 lux Extreme of darkest storm clouds, sunset or sunrise 101 1 decalux 40 lux Fully overcast, sunset or sunrise 102 1 hectolux < 200 lux Extreme of darkest storm clouds, midday 400 lux Sunrise or sunset on a clear day (ambient illumination) 104 10 kilolux 10–25 kilolux Typical overcast day, midday 20 kilolux Shade illuminated by entire clear blue sky, midday 105 100 kilolux 110 kilolux Bright sunlight 120 kilolux Brightest sunlight
Luminance This section lists examples of luminances, measured in candelas per square metre and grouped by order of magnitude.
Factor(cd/m2) Multiple Value Item 10−6 μcd/m2 Absolute threshold of vision 10−5 10−4 10−3 mcd/m2 Cloudy night sky without moon "Darkest sky" Night sky Typical photographic scene lit by full moon 10−2 Approximate scotopic/mesopic threshold 10−1 100 cd/m2 Floodlit buildings, monuments, and fountains 101 Approximate mesopic/photopic threshold Typical photographic scene at sunrise or sunset Green electroluminescent source 102 Standard SMPTE cinema screen luminance Monitor white in the sRGB reference viewing environment Peak luminance of a typical LCD monitor Typical photographic scene on overcast day 103 kcd/m2 Cloudy sky at noon Average cloudy sky Moon surface Clear sky 104 Typical photographic scene in full sunlight Average clear sky Clear sky at noon White illuminated cloud Fluorescent lamp 105 Low pressure sodium-vapor lamp Frosted incandescent light bulb 106 Mcd/m2 Solar disk at horizon 107 Filament of a clear incandescent lamp 108 Possible retinal damage 109 Gcd/m2 Solar disk at noon
See also Photometry (optics) Extraterrestrial sky
Notes and references
(see http://retina.anatomy.upenn.edu/~rob/lance/articles.html for the references within)
based on Orders of magnitude (illuminance), assuming a typical photographic scene has the same reflectance as an 18% gray card
based on this table of exposure values, assuming a reflected-light meter calibration constant of 12.5 cd·s/m2
When sources quote wide ranges of possible values, a (rounded) geometric mean of those values is reported here. The luminance of the sky in particular, varies by location, season, weather, time of day and part of the sky. The sky near the horizon is often about half as bright as at zenith, which in turn is often about half as bright as the sky near the Sun. Dr. Andrew J. Marsh has created an interactive web application that can be used to visualise different sky conditions.