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The troland (symbol Td), 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. 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 milimeter. [1]

The troland typically refers to the ordinary or photopic troland, which is defined in terms of the photopic luminance:

 \mathrm{T} =  \mathrm{L} \times \mathrm{p}

where L is the photopic luminance in cd m-2 and p is pupil area in mm2

A scotopic troland is also sometimes defined:

 \mathrm{T'} =  \mathrm{L'} \times \mathrm{p}

where L′ is the scotopic luminance in cd m-2 and p is pupil area in mm2

Conversions to other units[edit]

1 troland 10 kcd/m^2 (kilocandelas per square meter)
10000 cd/m^2 (candelas per square meter)
1×10^7 mcd/m^2 (millicandelas per square meter)
1×10^10 mucd/m^2 (microcandelas per square meter)
1 cd/cm^2 (candela per square centimeter)
3.142 La (lamberts) (unit officially deprecated)
2919 footlamberts (unit officially deprecated)
2919 equivalent foot-candles (unit officially deprecated)
31416 blondels (unit officially deprecated)
10000 nit (nits) (unit officially deprecated)
3.142×10^7 skots (unit officially deprecated)
1 stilb (unit officially deprecated)


Conversions from Other Units[edit]

1 kcd/m^2 0.1 trolands
1 cd/m^2 1×10^-4 trolands
1 mcd/m^2 1×10^-7 trolands
1 mucd/m^2 1×10^-10 trolands
1 cd/cm^2 1 troland
1 La 0.3183 trolands
1 footlambert 3.426×10^-4 trolands
1 equivalent foot-candle 3.426×10^-4 trolands
1 blondel 3.183×10^-5 trolands
1 nit 1×10^-4 trolands
1 skot 3.183×10^-8 trolands
1 stilb 1 troland


Physical quantities[edit]

  • luminance
  • equivalent luminance [2]

Unit system[edit]

centimeter-gram-second (cgs) [2]

Basic unit dimensions[edit]

[length]^(-2) [luminous intensity] [2]


  • ≈ 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 )[2]

See also[edit]