Troland
Encyclopedia
The troland named after Leonard T. Troland
, is a unit of conventional retinal illuminance. It is meant as a method for correcting photometric
measurements of luminance
values impinging on the human eye
by scaling them by the effective pupil
size.
The troland typically refers to the ordinary or photopic troland, which is defined in terms of the photopic luminance:
where L is the photopic luminance in cd
/m2
and p is pupil area in mm2
A scotopic troland is also sometimes defined:
Leonard T. Troland
Leonard T. Troland was an American physicist.He graduated in 1912 from the Massachusetts Institute of Technology with a degree in biochemistry. He then studied psychology at Harvard, where he obtained a Ph.D. in 1915. He worked for a year as a Harvard Travelling fellow at the General Electric...
, is a unit of conventional retinal illuminance. It is meant as a method for correcting photometric
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...
measurements of luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
values impinging on the human eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
by scaling them by the effective pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
size.
The troland typically refers to the ordinary or photopic troland, which is defined in terms of the photopic luminance:
- T = L·p
where L is the photopic luminance in cd
Candela
The candela is the SI base unit of luminous intensity; that is, power emitted by a light source in a particular direction, weighted by the luminosity function . A common candle emits light with a luminous intensity of roughly one candela...
/m2
Square metre
The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...
and p is pupil area in mm2
A scotopic troland is also sometimes defined:
- T′ = L′·p