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 press is no substitute for institutions. It is like the beam of a searchlight that moves restlessly about, bringing one episode and then another out of darkness into vision. Men cannot do the work of the world by this light alone. They cannot govern society by episodes, incidents, and eruptions. It is only when they work by a steady light of their own, that the press, when it is turned upon them, reveals a situation intelligible enough for a popular decision.”
—Walter Lippmann (1889–1974)
“Many women are surprised by the intensity of their maternal pull and the conflict it brings to their competing roles. This is the precise point at which many women feel the stress of the work/family dilemma most keenly. They realize that they may have a price to pay for wanting to be both professionals and mothers. They feel guilty for not being at work, and angry for being manipulated into feeling this guilt. . . . They don’t quite fit at home. They don’t quite fit at work.”
—Deborah J. Swiss (20th century)