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:
“Dark is the world, where your light shined never;
Well is he born, that may behold you ever.”
—Edmund Spenser (1552?–1599)
“As siblings we were inextricably bound, even though our connections were loose and frayed.... And each time we met, we discovered to our surprise and dismay how quickly the intensity of childhood feelings reappeared.... No matter how old we got or how often we tried to show another face, reality was filtered through yesterday’s memories.”
—Jane Mersky Leder (20th century)