A

area

A ₁, A ₂, A _s, A _d

area of surface 1, surface 2, a source, a detector, respectively

A _r

area of an image on the retina of a human eye

A _p

area of the pupil of a human eye

A _in, A _out, A _sph

area of an input port, output port, and sphere surface, respectively

b

distance from optic axis

c

the speed of light in a vacuum

C _e

photon-to-electron conversion efficiency , i.e., quantum efficiency of a photodetector

D

diameter

dA

infinitesimal element of area

dA ₁, dA ₂, dA _s, dA _d

infinitesimal element of area of surface 1, surface 2, a source, a detector, respectively

dL _?

infinitesimal change in radiance per wavelength interval

dT

infinitesimal change in temperature

d ? _l2

infinitesimal amount of radiant power transferred from point 1 to point 2

d ?

infinitesimal wavelength interval

d ?

infinitesimal frequency interval

d ?

infinitesimal change in solid angle

E

irradiance, the incident radiant power per the projected area of a surface

E _?

illuminance, the photometric equivalent of irradiance

E _r

average illuminance in an image on the retina of a human eye

E _T

retinal illuminance in units of trolands

E _T( ?)

photopic retinal illuminance from a monochromatic source in trolands

scotoptic retinal illuminance from a monochromatic source...