Skot (unit)

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Skot (symbol: sk) is an old and deprecated measurement unit of luminance, used for self-luminous objects (dark luminance). [1] [2] [3] The term comes from Greek skotos, meaning "darkness".

Contents

Overview

The skot to measure the dark luminance (Dunkelleuchtdichte) was introduced in 1940 by the German Lighting Society  [ de ] (Deutsche Lichttechnische Gesellschaft, LiTG) out of a necessity to describe the luminance of self-luminous objects, which differed so much from that of other objects that it was impractical to describe it using commonly used luminance values. [4] [2] [5] [1] Conversion factors for so called "scotopic stilb" (Skotopisches Stilb) depend on the spectral distribution of the light and were therefore redefined in 1948 by the International Commission on Illumination (Internationale Beleuchtungskommission, IBK) for a specific color temperature of 2042  K [6] [3] or 2046 K, [2] the temperature of solidification of platinum. Before 1948, the definition was based on a temperature of 2360 K [2] [3] as emitted by a wolfram-vacuum lamp. [7] [6] At this temperature, 1 sk = 10−3  asb. [3] The maximum allowed value is 10 skot to avoid the unit being used up into areas of mixed scotopic and photopic vision of the eye. [2]

Unit conversions

Units of luminance
 cd/m2 (SI unit)
≡ nit ≡ lm/m2/sr		 stilb (sb) (CGS unit)
≡ cd/cm2		 apostilb (asb)
≡ blondel		 bril skot (sk) lambert (L) foot-lambert (fL)
= 1 ⁄π cd/ft2
1 cd/m2=110−4π
≈ 3.142		107π
≈ 3.142×107		103π
≈ 3.142×103		10−4π
≈ 3.142×10−4		0.30482π
≈ 0.2919
1 sb=1041104π
≈ 3.142×104		1011π
≈ 3.142×1011		107π
≈ 3.142×107		π
≈ 3.142		30.482π
≈ 2919
1 asb=1 ⁄π
≈ 0.3183		10−4⁄π
≈ 3.183×10−5		110710310−40.30482
≈ 0.09290
1 bril=10−7⁄π
≈ 3.183×10−8		10−11⁄π
≈ 3.183×10−12		10−7110−410−110.30482×10−7
≈ 9.290×10−9
1 sk=10−3⁄π
≈ 3.183×10−4		10−7⁄π
≈ 3.183×10−8		10−3104110−70.30482×10−3
≈ 9.290×10−5
1 L=104⁄π
≈ 3183		1 ⁄π
≈ 0.3183		104101110710.30482×104
≈ 929.0
1 fL=1 ⁄ 0.30482⁄π
≈ 3.426		1 ⁄ 30.482⁄π
≈ 3.426×10−4		 1 ⁄ 0.30482
≈ 10.76		107⁄ 0.30482
≈ 1.076×108		103⁄ 0.30482
≈ 1.076×104		10−4⁄ 0.30482
≈ 1.076×10−3		1

See also

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References

  1. 1 2 Keplinger, Thomas (2021-03-29). "1939 bis 1945 – Im Keller glüht das Lumogen". Worte im Dunkel (in Austrian German). Vienna, Austria. Archived from the original on 2023-03-16. Retrieved 2023-03-16. Skot und Nox […] Interessant ist in diesem Zusammenhang die Einführung neuer Messeinheiten. Die Voraussetzungen der Forschung beziehungsweise die Erfordernisse an die Leuchtfarben unterschieden sich so stark von allen bis dahin erforschten Gebieten, dass die Deutsche Lichttechnische Gesellschaft  [ de ] 1940 eigene Einheiten ins Leben rief: Die Dunkelleuchtdichte wurde in Skot und die Dunkelbeleuchtungsstärke in Nox gemessen. [A] Diese Einheiten grenzten an die bereits bestehenden Größen der Leuchtdichte und Beleuchtungsstärke an und dienten der zahlenmäßigen Erfassung geringster Lichtwerte. So entsprach etwa ein Nox 10−3  Lux.
  2. 1 2 3 4 5 Westphal, Wilhelm Heinrich (1952). "Nox, Dunkelleuchtdichte, Skot". Physikalisches Wörterbuch (in German) (1 ed.). Berlin / Göttingen / Heidelberg, Germany: Springer-Verlag OHG. pp. 125, 271, 389. doi:10.1007/978-3-662-12706-3. ISBN   978-3-662-12707-0 . Retrieved 2023-03-16. pp. 271, 389: Dunkelleuchtdichte. […] Ist das Auge dunkeladaptiert, d.h. einer Leuchtdichte von weniger als 0,01  asb ausgesetzt, so gilt infolge des Purkinje-Phänomens eine von der spektralen Hellempfindlichkeitskurve abweichende, nach dem kurzwelligen Ende des Spektrums hin verschobene Empfindlichkeitskurve des Auges, die Stäbchenkurve des Dämmerungssehens. Unter Zugrundelegung dieser Empfindlichkeitskurve hat man 1940 in Deutschland die Dunkelleuchtdichte mit der Einheit Skot (sk) so festgesetzt, daß bei einem Licht der Farbtemperatur 2360  °K 1 sk = 10−3 asb gilt. 1948 ist von der Internationalen Beleuchtungskommission (IBK) die Bezugstemperatur auf 2046 °K, die Erstarrungstemperatur des Platins, festgesetzt worden. Die Bezeichnung Skot wurde von der IBK nicht übernommen, dafür soll "skotopisches Stilb" gesagt werden. Als höchstzulässiger Grenzwert für die Dunkelleuchtdichte ist in Deutschland 10 Skot festgesetzt worden, um eine Verwendung der Dunkelleuchtdichte im Gebiet des gemischten Zapfen- und Stäbchensehens zu vermeiden, da in diesem Bereich die photometrischen Maßgrößen wegen der allmählich gleitenden Augenempfindlichkeitskurve ihren Sinn verlieren. […] Skot, abgek[ürzt] sk, Einheit für die Dunkelleuchtdichte, welche für zahlenmäßige Angaben und zum Anschluß der Dunkelleuchtdichte an die normale Leuchtdichte 1940 von der Deutschen Lichttechnischen Gesellschaft  [ de ] geschaffen wurde. Für diesen Anschluß wurde die Strahlung des schwarzen Körpers bei T = 2360 °K, d.h. eine Strahlung der Farbtemperatur T1 = 2360 °K vereinbart. Eine Lichtquelle strahlt mit der Dunkelleuchtdichte 1 sk, wenn sie photometrisch gleich einer Strahlung der Farbtemperatur T2 = 2360 °K und der Leuchtdichte von 10−3 asb (Apostilb) ist. Bei der Farbtemperatur T1 = 2360 °K gilt also die Relation: 1 sk = 10−3 asb = 10−7/π sb. Ist die physikalische Strahlungsleistung Sλ einer beliebigen Lichtquelle als Funktion der Wellenlänge bekannt, so läßt sich zwischen den Zahlenwerten ihrer Leuchtdichte B gemessen in 10−3 asb, und ihrer Dunkelleuchtdichte B, gemessen in sk, die Verknüpfungsbeziehung {B}sk = (2,161 ± 0,001) {B}10−3 asb ∫ SλVλ,Wdλ / ∫ SλVλdλ angeben, wobei Vλ die relative spektrale Hellempfindlichkeit und Vλ,W die relative spektrale Dämmerungsempfindlichkeit nach Weaver [B] [C] bedeuten.
  3. 1 2 3 4 Grimsehl, Ernst [in German]; Schallreuter, Walter [in German] (1988) [1976]. "1. Licht: 1.4. Photometrie: 1.4.1. Grundbegriffe". In Haferkorn, Heinz (ed.). Lehrbuch der Physik: Optik (in German). Vol. 3 (19 ed.). Leipzig, Germany: BSB BG Teubner Verlagsgesellschaft. pp. 33–38 [37–38]. doi:10.1007/978-3-322-96431-1. ISBN   978-3-322-96432-8. Order No. 6666211, VLN 294-375/84/88, LSV 1164. Retrieved 2023-03-16. pp. 37–38: Dunkelsehen […] Für das Dunkelsehen, bei dem nur die Stäbchen angeregt werden, definiert man die Dunkelleuchtdichte mit der Einheit Skot (sk) und die Dunkelbeleuchtungsstärke mit der Einheit Nox (nx). Die Umrechnungsfaktoren zwischen den Hell- und Dunkelgrößen hängen von der spektralen Zusammensetzung des Lichtes ab. Sie werden deshalb für die Farbtemperatur 2042  K (früher 2360 K) festgelegt. Bei dieser ist 1 sk = 10−3  asb und 1 nx = 10−3  lx.
  4. ↑ Dresler, Albert [in German] (1940) [February 1940, June 1940, July 1940]. Written at Berlin, Germany. "Messung und Berechnung von "Dunkelleuchtdichte" und "Dunkelbeleuchtungsstärke"". Das Licht (in German). Vol. 10, no. 2, 6, 7. Munich, Germany: Deutsche Lichttechnische Gesellschaft  [ de ] / Richard Pflaum Verlag GmbH & Co. KG. pp. 37, 103, 112, 118–120, 145–146. ISSN   0024-2861.
  5. ↑ Trendelenburg, Wilhelm; Monjé, Manfred [in German]; Schmidt, Ingeborg; Schütz, Erich [in German] (1961) [1943]. "II. Die Gesichtsempfindungen F. Das Nachtsehen und seine Beziehungen zum Tagessehen 5. Tageswerte der Spektralstrahlungen - Technische Lichtmessung b) Technische Lichtmessung". In Trendelenburg, Wilhelm; Schütz, Erich [in German] (eds.). Der Gesichtssinn - Grundzüge der Physiologischen Optik [The sense of sight - Principles of physiological optics]. Lehrbuch der Physiologie (in German) (2nd illustrated ed.). Springer-Verlag Berlin Heidelberg GmbH. p. 139–147 [144]. doi:10.1007/978-3-662-22085-6. ISBN   978-3-662-22086-3 . Retrieved 2023-03-25. p. 144: […] Die physiologischen (psychophysischen) Begriffe und Einheiten werden auf Grund der physikalisch meßbaren Strahlungsleistung auf den Gesichtssinn aufgestellt. Mit Ausnahme der Einheiten Skot und Nox beziehen sich alle auf das helladaptierte Auge. […] (xii+440 pages)
  6. 1 2 Stille, Ulrich [in German] (1965). "Fünfter Teil: Akustik und Phonometrie - optische Strahlung und Photometrie; Kapitel II: Größenarten der optischen Strahlung und Photometrie; 2. Spezielle Lichteinheiten / 3. Photometrisches Strahlungsäquivalent und (mechanisches) Lichtäquivalent". Messen und Rechnen in der Physik: Grundlagen der Grösseneinführung und Einheitenfestlegung (in German) (2nd improved and expanded ed.). Wiesbaden, Germany: Springer Fachmedien Wiesbaden GmbH. pp. 261–262 [262], 274–275 [275], 421. doi:10.1007/978-3-322-98458-6. ISBN   978-3-322-97920-9 . Retrieved 2023-03-20. (xii+471 pages)
  7. ↑ Lohse, Bernhard; Stille, Ulrich [in German] (January 1948) [1947-08-19]. Written at Braunschweig, Germany. Deutsche Physikalische Gesellschaft (ed.). "Einführung und Bestimmung des Lichtäquivalents". Zeitschrift für Physik (in German). 125 (1–3). Berlin / Göttingen / Heidelberg, Germany: Springer-Verlag: 133–158. Bibcode:1948ZPhy..125..133L. doi:10.1007/BF01337623. ISSN   0044-3328. S2CID   125512557 . Retrieved 2023-03-19.

Further reading

SI photometry quantities
QuantityUnitDimension
[nb 1] 		Notes
NameSymbol [nb 2] NameSymbol
Luminous energy Qv [nb 3] lumen second lm⋅sT⋅JThe lumen second is sometimes called the talbot.
Luminous flux, luminous powerΦ v [nb 3] lumen (= candela steradian)lm (= cd⋅sr)JLuminous energy per unit time
Luminous intensity Iv candela (= lumen per steradian) cd (= lm/sr)JLuminous flux per unit solid angle
Luminance Lv candela per square metre cd/m2 (= lm/(sr⋅m2))L−2⋅JLuminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit .
Illuminance Ev lux (= lumen per square metre) lx (= lm/m2)L−2⋅JLuminous flux incident on a surface
Luminous exitance, luminous emittanceMvlumen per square metrelm/m2L−2⋅JLuminous flux emitted from a surface
Luminous exposure Hv lux second lx⋅sL−2⋅T⋅JTime-integrated illuminance
Luminous energy densityωvlumen second per cubic metrelm⋅s/m3L−3⋅T⋅J
Luminous efficacy (of radiation)Klumen per watt lm/W M−1⋅L−2⋅T3⋅JRatio of luminous flux to radiant flux
Luminous efficacy (of a source)η [nb 3] lumen per watt lm/W M−1⋅L−2⋅T3⋅JRatio of luminous flux to power consumption
Luminous efficiency, luminous coefficientV1Luminous efficacy normalized by the maximum possible efficacy
See also:
  1. ↑ The symbols in this column denote dimensions; "L", "T" and "J" are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule.
  2. ↑ Standards organizations recommend that photometric quantities be denoted with a subscript "v" (for "visual") to avoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967
  3. 1 2 3 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.
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