Thanks to authorization from the International Commission of Illumination (CIE),
some of the definitions have been reproduced from the CIE International
Lighting Vocabulary, publication 17.4-1987.
Access the CIE web site.

écart moyen (FR)
mittlere Abweichung (DE)
middelfeil (NO)

mean bias deviation

Unit: %

Quantity defined by the formula:

Used to characterize the bias of a model. Negative, if the model underpredicts, positive, if it overpredicts.

méridien (FR)
Meridian (DE)
meridiano (ES)
meridiano (IT)
meridian [NO]


Considering a great circle on the surface of the earth passing through the poles, a meridian is the half of this circle included between the poles.

 facteur de transmission normale (FR)
normale Tansmission (DE)
transmitancia normal (ES)
fattore di transmissione normale (IT)
vinkelrett transmittans;
vinkelrett transmisjonsfaktor (NO)

normal transmittance

Unit: 1

Ratio of the transmitted radiant or luminous flux to the incident flux striking the material in a direction perpendicular to its surface.

épaisseur optique
de l'atmosphère (FR)
Optische Dicke
der Atmosphäre (DE)
Espesor óptico
de la atmósfera (ES)
Spessore ottico
verticale dell'atmosfera (IT)
Optische dichtheid
van de atmosfeer (NL)
atmosfærens optiske tykkelse (NO)
Gestosé optyczna atmosfery (PL)
Atmosfärens optiska täthet (SE)

optical thickness of the atmosphere

Unit: 1

CIE. Quantity defined by the formula:

Where is the radiant flux of a collimated beam entering the upper limit layers of the atmosphere at an angle to the vertical, and the attenuated radiant flux of that beam reaching the surface of the Earth. (In English, the term optical depth is sometimes used instead of optical thickness).

observateur de référence
photométrique CIE (FR)
Normalbeobachter CIE (DE)
observador fotométrico
patron CIE (ES)
osservatore fotometrico CIE (IT)
(van der CIE) (NL)
CIE fotometriske
standardobservatør (NO)
obserwator fotometryczny
CIE normalny (PL)
CIE standardobservatör
för fotometri (SE)


photometric observer CIE standard

CIE. Ideal observer having a relative spectral responsivity curve that conforms to the for photopic vision and that complies with the summation law implied in the definition of luminous flux.

vision photopique (FR)
Tagessehen; photopisches
Sehen (DE)
visión fotópica (ES)
visione fotopica (IT)
fotopisch zien (NL)
fotopisk syn; dagssyn (NO)
widzenie fotopowe (PL)
fotopiskt seende; dagseende (SE)


photopic vision

CIE. Vision by the normal eye when it is adapted to levels of luminance of at least several candelas per square meter (i.e. under daylight).

pixel (FR)
Bildelement, Pixel (DE)
pixel (ES)
pixel (IT)
pixel (NO)



A small discrete element which with other elements, consitutes an image.

luminance énergétique;
radiance (FR)
Radianz; Strahldichte (DE)
radiancia (ES)
radianza (IT)
radiantie (NL)
radians (NO)
luminancja energetyczna (PL)
radians (SE)

radiance (in a given direction, at a given point of a real or imaginary surface)

Unit: W/(

CIE. Quantity defined by the formula:

Where is the radiant flux transmitted by an elementary beam passing through the given point and propagating in the solid angle containing the given direction: is the area of a section of that beam containing the given point: is the angle between the normal to that section and the direction of the beam.

flux énergétique (FR)
Strahlungsleistung (DE)
flujo radiante (ES)
flusso energetico (IT)
stralingsvermogen (NL)
strålingsfluks (NO)
strumien energetyczny;
strumien promienisty (PL)
stralningsflöde;stralningseffekt (SE)

radiant flux ; radiant power

Unit : W

CIE. Power emitted, transmitted or received in the form of radiation.

atmosphère de Rayleigh (FR)
Rayleigh Atmosphäre (DE)
atmósfera de Rayleigh (ES)
atmosfera di Rayleigh (IT)
atmosfeer de Rayleigh (NL)

Rayleigh atmosphere

An ideal atmosphere containing only air molecules (the earth atmosphere also contains aerosols, cloud droplets and ice crystals). Used by Rayleigh in 1871 to discover one of the most important example of a physical law of light scattering.

facteur de réflexion (FR)
Reflexionsgrad (DE)
reflectancia (ES)
fattore di riflessione (IT)
reflectiefactor (NL)
reflektans; refleksjonsfaktor (NO)
wspolczynnik odbicia (PL)
reflektans; reflexionsfaktor (SE)

reflectance (for incident radiation of given spectral composition, polarization and geometrical distribution)

Unit: 1

CIE. Ratio of the reflected radiant or luminous flux to the incident flux in the given conditions. The reflectance is also called the albedo for a radiant flux.

masse d’air optique
relative (FR)
relative optische
Luftmasse (DE)
masa optica del aire relativa (ES)
massa ottica relativa dell’aria (IT)
relatieve optische luchtmassa (NL)
relativ optisk luftmasse (NO)
gaestosv optyczna
atmosfery wzgledna (PL)
relativ optisk luftmassa (SE)

relative optical air mass

Unit: 1

CIE. Ratio of the slant optical thickness to the vertical optical thickness of the atmosphere . When the curvature of the atmosphere and atmospheric refraction are neglected, we have: .

écart quadratique moyen (FR)
Wurzel der mittleren
quadratischen Abweichung (DE)
roten av midlere kvadratfeil (NO)

root mean square deviation

Unit: %

Quantity defined by the formula:

Used to characterize the bias of a model in absolute terms.