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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
In photography, light value has been used to refer to a "light level" for either incident or reflected light, often on a base-2 logarithmic scale. The term does not derive from a published standard, and has had several different meanings:
In APEX, 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.
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In photography, light value has been used to refer to a "light level" for either incident or reflected light, often on a base-2 logarithmic 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 'LV', in this sense. The Honeywell/Pentax 1°/21° spot meter indicated in "light level" ("LL"), with LL essentially exposure value (EV) for ISO 100 film speed. 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). Zakia and Stroebel (1993) and Stroebel, Compton, Current, and Zakia (2000) used the term in this sense. They used the APEX symbol B v {\displaystyle 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 {\displaystyle L_{v}} . The table at the end of the article used units of illuminance and the symbol B v {\displaystyle B_{v}} , as noted above. A synonym for exposure value (EV) (e.g., Kyoritsu calibrated light sources, 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". This usage appears on many web pages, usually without attribution of an authoritative source. Eads (2000) proposed a revised APEX 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 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 (EV) elsewhere. In APEX, 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.
The light reflectance value (LRV) is a value for the reflectance of light on a scale from 0 to 1, with zero indicating no reflected light and one indicating complete reflection of light. Reflectance is the proportion of the total electromagnetic energy (EM) that is reflected, making it not a measure of the absolute amount energy in the reflection, but a ratio of the reflected energy to the total energy. Light reflectance values are used in a variety of applications, from architecture to ecology to cartography, and can indicate how visible an interior is for those with visual impairments to being able to estimate the biomass of a forest from space.
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 have the same EV (for any fixed scene luminance). Exposure value is also used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop. The EV concept was developed by the German shutter manufacturer Friedrich Deckel in the 1950s. Its intent was to simplify choosing among equivalent camera exposure settings by replacing combinations of shutter speed and f-number (e.g., 1/125 s at f/16) with a single number (e.g., 15). On some lenses with leaf shutters, the process was further simplified by allowing the shutter and aperture controls to be linked such that, when one was changed, the other was automatically adjusted to maintain the same exposure. This was especially helpful to beginners with limited understanding of the effects of shutter speed and aperture and the relationship between them. But it was also useful for experienced photographers who might choose a shutter speed to stop motion or an f-number for depth of field, because it allowed for faster adjustment—without the need for mental calculations—and reduced the chance of error when making the adjustment. The concept became known as the Light Value System (LVS) in Europe; it was generally known as the Exposure Value System (EVS) when the features became available on cameras in the United States. Because of mechanical considerations, the coupling of shutter and aperture was limited to lenses with leaf shutters; however, various automatic exposure modes now work to somewhat the same effect in cameras with focal-plane shutters. The proper EV was determined by the scene luminance and film speed; it was intended that the system also include adjustment for filters, exposure compensation, and other variables. With all of these elements included, the camera would be set by transferring the single number thus determined. Exposure value has been indicated in various ways. The ASA and ANSI standards used the quantity symbol Ev, with the subscript v indicating the logarithmic value; this symbol continues to be used in ISO standards, but the acronym "EV" is more common elsewhere. The Exif standard uses "Ev". Although all camera settings with the same EV nominally give the same exposure, they do not necessarily give the same picture. The f-number (relative aperture) determines the depth of field, and the shutter speed (exposure time) determines the amount of motion blur, as illustrated by the two properly exposed images of the breaking wave.
Monochrome photography is photography in which each position on an image can record and show a different amount of light (value), but not a different color (hue). The majority of monochrome photographs produced today are black-and-white, either from a gelatin silver process, or as digital photography. Other hues besides grey can be used to create monochrome photography, but brown and sepia tones are the result of older processes like the albumen print, and cyan tones are the product of cyanotype prints. As monochrome photography provides an inherently less complete reproduction than color photography, it is mostly used for artistic purposes and certain technical imaging applications.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
