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Guide to Light Measurement Units

Light Measurement Units

The table below lists the quantities, units and notation used in radiometry and photometry.

Quantity

Notation

Unit

Solid Angle

W

steradian (sr)

Wavelength

l

nanometer (nm) = 10-9 meters

Radiant Flux

Fe

Watt (W)

Radiance

Le

Watt per steradian per sq. meter (W/sr.m2)

Radiant Intensity

Ie

Watt per steradian (W/sr)

Irradiance

Ee

Watt per sq. meter (W/m2)

Radiant Exitance

 Me

Watt per sq. meter (W/m2)

Luminous Flux

 Fv

lumen (lm)
1 Watt of monochromatic light at 555nm equals 683 lumens 

Luminance

 Lv

candela per sq. meter (cd/m2)
1 cd/m2 = 1 lumen per steradian per sq. meter (lm/sr.m2) = 1 nit
 

Luminous Intensity

Iv

 candela (cd)
1 cd = 1
lumen per steradian (lm/sr)

Illuminance

 Ev

lux
1 lux = 1 lumen per sq. meter (lm/m2)
 

Luminous Exitance

 Mv

 lumen per sq. meter (lm/m2)

Luminous Energy

 Qv

 lumen second (lm.s) = Talbot

Luminous Exposure

 Hv

 lux second (lx.s)

 

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