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__NOTOC__ In
photography Photography is the visual arts, art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is empl ...
, light value has been used to refer to a "light level" for either incident or reflected light, often on a base-2
logarithm In mathematics, the logarithm of a number is the exponent by which another fixed value, the base, must be raised to produce that number. For example, the logarithm of to base is , because is to the rd power: . More generally, if , the ...
ic scale. The term does not derive from a published standard, and has had several different meanings: # An arbitrary value indicated by an exposure meter such as the Weston Master V, discussed in Adams (1948, 14–18). This may have been the origin of the term. The indicated light value was transferred to the meter's exposure calculator, which then was used to determine camera settings. Ray (2000) uses the term, with the
acronym An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial Letter (alphabet), letter of each wor ...
'LV', in this sense. The
Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building automation, industrial automa ...
/
Pentax was a Japanese camera and optical equipment manufacturer. Currently, it exists as the Pentax Life Care Business Division of Hoya's medical endoscope business, as well as the digital camera brand of Ricoh Imaging, a subsidiary of Ricoh. Penta ...
1°/21° spot meter indicated in "light level" ("LL"), with LL essentially
exposure value In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure (photography), exposure have the same EV (for any fixed scene luminanc ...
(EV) for ISO 100
film speed Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in 1974. A closely related system, also known as IS ...
. The later Pentax Spotmeter V and Digital Spotmeter indicated directly in EV for ISO 100, but they made no mention of "light level", "light value", or LV. # A synonym for incident light value, from the Additive system of Photographic EXposure (
APEX The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...
). Zakia and Stroebel (1993) and Stroebel, Compton, Current, and Zakia (2000) used the term in this sense. They used the APEX symbol B_v, normally used for luminance value. # An apparent synonym for luminance value, from APEX. Stroebel, Compton, Current, and Zakia (2000) referred to "scene illuminance" in the text of the article, but the example used units of luminance. The defining equation used the symbol L_v. The table at the end of the article used units of illuminance and the symbol B_v, as noted above. # A synonym for exposure value (EV) (e.g., Kyoritsu calibrated light sources,Specifications for Kyoritsu testers and calibrated light sources are available on th
C.R.I.S. Camera Services
web site under "kyoritsu test equipment".
for which the luminance ranges are specified in terms of "LV at ISO 100". Kyoritsu specify the luminance ranges of their multi-function camera testers in EV, presumably at ISO 100). # A synonym for "EV at ISO 100
film speed Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in 1974. A closely related system, also known as IS ...
". This usage appears on many web pages, usually without attribution of an authoritative source. Eads (2000) proposed a revised
APEX The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...
in which luminance value was equal to EV for ISO 100 speed, but he did not use the term ''light value''. # Literally speaking, the English term ''light value'' could be translated as "Lichtwert" in German language, however, this is ''not'' what the term ''Lichtwert'', as it was introduced by the German shutter manufacturer
Friedrich Deckel Friedrich Deckel GmbH, also known as F.Deckel, was a German company founded by Friedrich Deckel and Christian Bruns in Munich as Bruns & Deckel in 1903. Its most famous product is the ''Compur'' line of leaf shutters used on many photographic lense ...
in 1954 and defined as ''Belichtungswert'' in DIN 19010, is used for in German-speaking countries. Instead, the established term ''Lichtwert'' (abbreviated as "LW") describes what became known as
exposure value In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure (photography), exposure have the same EV (for any fixed scene luminanc ...
(EV) elsewhere. In
APEX The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...
, luminance value and incident light value are numerically equal, so that for a given "light value", either meaning 2 or 3 would result in the same camera settings.


Notes


See also

*
APEX system APEX stands for Additive System of Photographic Exposure, which was proposed in the 1960 ASA standard for monochrome film speed, ASA PH2.5-1960, as a means of simplifying exposure computation. Exposure equation Until the late 1960s, cameras di ...
*
Exposure value In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure (photography), exposure have the same EV (for any fixed scene luminanc ...
* Sunny 16 rule


References

* Adams, Ansel. 1948. ''The Negative: Exposure and Development''. Boston: New York Graphic Society. * Eads, Andrew C. 2000. "Simplifying and Understanding Photographic Exposure with the APEx System", ''PHOTO Techniques'', Jan/Feb 2000, 54–59. * Ray, Sidney F. 2000. "Camera Exposure Determination". In ''The Manual of Photography,'' 9th ed. Oxford: Focal Press. * Stroebel, Leslie, John Compton, Ira Current, and Richard D. Zakia. 2000. ''Basic Photographic Materials and Processes,'' 2nd ed. Boston: Focal Press. * Zakia, Richard D. and Leslie Stroebel, eds. 1993. ''Focal Encyclopedia of Photography,'' 3rd ed. Boston: Focal Press. Science of photography