troland
   HOME

TheInfoList



OR:

The troland (symbol Td), named after
Leonard T. Troland Leonard Thompson Troland (1889–1932) was an American physicist, psychologist and psychical researcher. Career Troland graduated in 1912 from the Massachusetts Institute of Technology with a degree in biochemistry. He then studied psychology at ...
, is a unit of ''conventional retinal illuminance''. It is meant as a method for correcting photometric measurements of
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, is emitted from, or is reflected from a particular area, and falls withi ...
values impinging on the
human eye The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. ...
by scaling them by the effective
pupil The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black ...
size. It is equal to retinal illuminance produced by a surface whose luminance is one nit when the apparent area of the entrance pupil of the eye is 1 square millimeter. The troland unit was proposed in 1916 by
Leonard T. Troland Leonard Thompson Troland (1889–1932) was an American physicist, psychologist and psychical researcher. Career Troland graduated in 1912 from the Massachusetts Institute of Technology with a degree in biochemistry. He then studied psychology at ...
, who called it a photon. The troland typically refers to the ordinary or
photopic Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108  cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visua ...
troland, which is defined in terms of the photopic luminance: : \mathrm = \mathrm \times \mathrm , where ''L'' is the photopic luminance in cd m−2 and ''p'' is pupil area in mm2. A
scotopic In the study of human visual perception, scotopic vision (or scotopia) is the vision of the eye under low-light conditions. The term comes from Greek ''skotos'', meaning "darkness", and ''-opia'', meaning "a condition of sight". In the human eye, ...
troland is also sometimes defined: : \mathrm = \mathrm \times \mathrm , where ''L′'' is the scotopic luminance in cd m−2 and ''p'' is pupil area in mm2. Although named "retinal illuminance" (and originally named "photon" by Troland), trolands do not measure the actual photon flux incident on the retina; that quantity depends on the specific wavelengths of light that constitute the luminance used in the calculation.


Units conversion

Troland does not directly convert to other units, being a retinal luminance per unit area of a pupil. However Troland is linked to retinal illuminance in as follows. Assuming the corneal luminance L from an extended source, the pupil diameter p and the focal length of the eye F, the retinal luminance is: Lr m / m^2 = pi * L / 4 / (f/#)^2 ~ pi * L * p^2 / 4 / F^2. Multiplying by the pupil area : Trolands d/m^2 \cdot mm^2=L \cdot \pi \cdot p^2/4 = F^2 \cdot Lr \approx 289 \cdot Lr. Alternatively, the retinal illuminance Lr m/m^2= Trolands / 289
m^2 The square metre ( international spelling as used by the International Bureau of Weights and Measures) or square meter (American spelling) is the unit of area in the International System of Units (SI) with symbol m2. It is the area of a square ...
/math> As provided by a more accurate optical calculations, the conversion factor is 278 rather than 289 as demonstrated by simplified considerations above. Sometimes (by convention only, although not rigorously accurate by definition), retinal luminance is expressed in d/m^2= m/sr /m^2/math>. Assuming a Lambertian surface, 1 cd/m^2 = pi lm/m^2 = pi lux. That is, 1 d/m^2= 289/pi
roland Roland (; frk, *Hrōþiland; lat-med, Hruodlandus or ''Rotholandus''; it, Orlando or ''Rolando''; died 15 August 778) was a Frankish military leader under Charlemagne who became one of the principal figures in the literary cycle known as the ...
~ 92
roland Roland (; frk, *Hrōþiland; lat-med, Hruodlandus or ''Rotholandus''; it, Orlando or ''Rolando''; died 15 August 778) was a Frankish military leader under Charlemagne who became one of the principal figures in the literary cycle known as the ...


Physical quantities

* luminance *equivalent luminance wolframalpha.com
/ref>


Unit system

centimeter-gram-second (cgs)


Basic unit dimensions

ength(-2) uminous intensity


Comparisons

* ≈ 0.8 × luminance of a kerosene candle (≈ 12000 cd/m^2 ) * ≈ luminance of a sperm candle (≈ 10000 cd/m^2 ) * ≈ luminance of an average daytime clear sky (≈ 8000 cd/m^2 )


See also

*
Leonard T. Troland Leonard Thompson Troland (1889–1932) was an American physicist, psychologist and psychical researcher. Career Troland graduated in 1912 from the Massachusetts Institute of Technology with a degree in biochemistry. He then studied psychology at ...
* Troland Research Awards


References

{{reflist Vision Non-SI metric units Units of illuminance