DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

ANSI/IESNA RP-16, Nomenclature
and Definitions for Illuminating
Engineering.
CIE N o 17 (E-1.1), International
Lighting Vocabulary (Vienna,
Austria: Commission Internationale
de L’Éclairage).
Differentiate
flux with
respect to
– radiant flux,
power (Φ, F, P)
area irradiance (E),
radiant exitance
(M)
Introduction to radiometry
and photometry B
The domain of radiometry involves optical power and
its spatial and angular distributions. Photometry is, in
essence, radiometry weighted by the spectral response
of vision. These fields involve several subtle concepts,
masked by a bewildering array of symbols and units.
I strive to sort out some of the confusion, and make
some suggestions concerning units and nomenclature.
Table B.1 below summarizes radiometric quantities,
symbols, and units (in the left columns) and the corresponding
photometric quantities, symbols, and units (to
the right). The symbol for a photometric quantity is just
the symbol for the corresponding radiometric quantity,
with the addition of the subscript v (for visual). Some
people add the subscript e to the radiometric symbols.
Radiometric (Radiant) Photometric (Luminous)
Quantity (Symbol) Unit Quantity (Symbol) Unit
watt, W luminous flux
(Φv , Fv , Pv )
W·m –2 illuminance (Ev )
luminous exitance
(Mv )
lumen, lm
lm·m –2
= lux, lx
solid angle radiant intensity (I) W·sr –1 luminous intensity lm·sr
(Iv )
–1
= candela, cd
area
and solid angle
radiance (L) W·m –2 ·sr –1 luminance (Lv , Y) cd·m –2
= nit
Table B.1 Quantities, symbols, and units of radiometry and photometry, In radiometry, the
symbol L v is used for luminance; however, luminance is denoted Y in color science and in video.
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