Several measures of light are commonly known as intensity. These are obtained by dividing either a power or a luminous flux by a solid angle, a planar area, or a combination of the two. The relationships are summarised in the table below:
| Radiometric | Photometric | |
|---|---|---|
| Angular | Radiant intensity, measured in watts per steradian (W/sr) | Luminous intensity, measured in lumens per steradian (lm/sr), or candela (cd) |
| Areal |
Irradiance, measured in watts per square meter (W/m2), called intensity in most branches of physics |
Several quantities measured in lumens per square meter (lm/m2), or lux (lx):
|
| Both | Radiance, commonly called intensity in astronomy and astrophysics (W·sr−1·m−2) | Luminance (lm·sr−1·m−2, or cd/m2) |
Famous quotes containing the words light and/or intensity:
“The light of her face falls from its flower,
as a hyacinth,
hidden in a far valley,
perishes upon burnt grass.”
—Hilda Doolittle (1886–1961)
“We may say that feelings have two kinds of intensity. One is the intensity of the feeling itself, by which loud sounds are distinguished from faint ones, luminous colors from dark ones, highly chromatic colors from almost neutral tints, etc. The other is the intensity of consciousness that lays hold of the feeling, which makes the ticking of a watch actually heard infinitely more vivid than a cannon shot remembered to have been heard a few minutes ago.”
—Charles Sanders Peirce (1839–1914)