Page 295 - Modern Optical Engineering The Design of Optical Systems

274 Chapter Twelve

Flux (Symbol F )
lumen defined in text, Eq. 12.18

Intensity (Symbol I) (also luminous pointance)
candela (colloq: “candle”) one lumen per steradian emitted from a point source.
2
1/60 of the intensity of one cm of a blackbody at 2042 K.
“old candle” 1.02 candela
carcel 9.6 candles
hefner 0.9 candles
Illumination (Symbol E) (also illuminance, luminous incidance, lum. areance)
2
footcandle one lumen per ft incident on a surface 10.76 lux
1/929 phot
2
4
phot (centimeter-candle) one lumen per cm 10 lux 929 ft cd
2
lux (meter-candle) one lumen per m .0929 ft cd
nox 0.001 lux
Brightness (Symbol B) (also luminance, luminous sterance)
2
candle per sq. cm. one lumen emitted per steradian per cm projected area
normal to direction
2
2
stilb one cd/cm 929 cd/ft lamberts 929 ft lamberts
lambert (1/ ) candles per cm 2
2
foot-lambert (1/ ) candles per m (1/929) lambert (1/ 929) stilb
meter-lambert apostilb 1000 skot 10 4 lamberts
nit one lux per ster .0001 stilb candel/m 2
skot 3.18 10 8 stilb 9.29 10 5 ft lamberts 2.957
10 5 cd/ft 2
The Troland is an annoying unit of retinal illumination produced by viewing a surface of
2
2
2
one cd/m brightnass when the pupil area is one mm . It equals 0.0035 lumens/m ; It equals
2
3.5 nano-lumens per cm ; It equals the number of nits times the pupil area in mm 2
Figure 12.10 Photometric quantities.

Radiant Intensity: J P/ Luminous Intensity: I F/
J is radiant intensity I is luminous intensity
P is the radiant power emitted F is the luminous flux emitted into
into solid angle solid angle

Irradiance: H J/S J Illumination (illuminance):
2
2
E I/S
H is the irradiance incident on a E is the illumination incident on a
surface a distance S from a point surface a distance S from a point
source of intensity J. is the solid source of intensity I. is the solid