By intrinsic brightness is meant the amount of light emitted per unit surface of the light source. Table XII gives the intrinsic brightness of several light sources.

Table XII. Intrinsic Brilliancies In Candle-Power Per Square Inch

Source

Brilliancy

NOTES>

Sun in zenith

G00,000

500,000

2,000

Rough equivalent values, taking account of absorption

Sun at 30 degrees elv.

Sun on horizon

Arc light

10,000) to

100,000

Maximum about 200,000 in crater

Calcium light

5,000

Nernst "glower"

1,000

Unshaded

Incandescent lamp

200-300

Depending on efficiency

Enclosed arc

75-100

Opalescent inner globe

Acetylene flame

75-100

Welsbach light

20 to 25

Kerosene light

4 to 8

Variable

Candle

3 to 4

Gas flame

3 to 8

Variable

Incandescent (frosted)

2 to 5

Opal shaded lamps, etc.

0.5 to 2