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illumination, in physics


in physics: see lightinglighting,
light produced by artificial means to allow visibility in enclosures and at night. For stage lighting, see scene design and stage lighting. Early Sources of Artificial Lighting
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; photometryphotometry
, branch of physics dealing with the measurement of the intensity of a source of light, such as an electric lamp, and with the intensity of light such a source may cast on a surface area.
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illumination, in art


in art, decoration of manuscripts and books with colored, gilded pictures, often referred to as miniatures (see miniature paintingminiature painting
[Ital.,=artwork, especially manuscript initial letters, done with the red lead pigment minium; the word originally had no implication as to size].
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); historiated and decorated initials; and ornamental border designs.

Early Illumination

The earliest known illustrated rolls come from Egypt; they include the oldest example, the Ramesseum Papyrus (c.1980 B.C.) and fragments from the Book of the Dead, found in tombs. Little or nothing survives of ancient Greek illumination, although scientific treatises and epic poetry are said to have contained pictures. It is thought that by the 2d cent. A.D. the long papyrus roll began to be replaced by the parchment codex (or leaved book). Thus a new, compact format was introduced as the framework for the picture. From the late classical period (probably 5th cent. A.D.) come the illustrations of Vergil (Vatican) and the Iliad (Ambrosian Library, Milan).

Illumination in Early Christendom

Most illuminations of the early Christian period, whose style was based on Hellenistic prototypes, are preserved only in medieval copies made in monasteries. Sumptuous Byzantine codices of the 6th and 7th cent., such as the Vienna Genesis, also show the adaptation of antique models to biblical subject matter.

In the 7th and 8th cent. the work of the Irish, Anglo-Saxons, Franks, and Lombards displayed rich decorative geometric designs with intricate human and animal interlacing, largely concentrated in initials and title pages. Among the masterpieces of Hiberno-Saxon illumination are the Book of Durrow, the Book of Kells (both: Trinity College Library, Dublin), and the Lindisfarne Gospels (British Mus.).

The chief works of the Carolingian period date from the beginning of the 9th cent. and were created for the court of Charlemagne, whose aim was to revive the art of antiquity. The existence of several local monastic schools led to a variety of styles; prominent were the Ada group, characterized by splendid coloring and figures full of movement and expression, e.g., The Gospel Book of Ada (Municipal Library, Trier), and the Reims school, known for vibrant pen drawings with little color, e.g., the Utrecht Psalter (9th cent.; University Library, Utrecht).

Works of the Reims school greatly influenced the English school of Winchester in the 10th and 11th cent. The Benedictional of St. Aethelwold (c.980) typifies this style, with sketchy drawings of elongated figures in fluttering drapery, enriched by foliated borders. Contemporary with the flowering of the Winchester school was the Ottonian renascence in Germany. Germanic illuminators used thick, luxurious colors with vigorous outlines and dynamic movement. Reichenau, Hildesheim, and Fulda were prominent centers of Ottonian art.

In Byzantine miniatures a more classical mode continued into the 13th cent. in such works as the Joshua Roll (10th cent.; Vatican), along with images of a hieratic austerity. Italy was important for the diffusion of the Byzantine style; the most original works are the Exultet rolls (Pisa), containing joyous hymns. Byzantine work declined after the capture of Constantinople in 1204.

In Spain, where there was a mixture of Christian and Arabic elements, a highly inventive work was the Commentary of Beatus on the Apocalypse (a 10th-century copy is in the Pierpont Morgan Library, New York City). The illumination of large books, Bibles and psalters, was fashionable in the Romanesque era. Richly decorated initials graced these books and, in the early 12th cent., stylized figures enhanced by complex garments and gestures were plentiful. Characteristic of mid-12th-century work is the Winchester Bible.

Before the 14th cent. illuminated manuscripts in the West were nearly always made of vellum. Both ink outline and full-color drawings were common. The color medium was usually temperatempera
, painting method in which finely ground pigment is mixed with a solidifying base such as albumen, fig sap, or thin glue. When used in mural painting it is also known as fresco secco (dry fresco) to distinguish it from the buon fresco
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, and the gilt was burnished to a high luster. Lavish illumination was most commonly applied to religious books, including early gospels, fashioned for rich patrons, then psalters and books of hoursbook of hours,
form of prayer book developed in the 14th cent. from the prayers of clerics appended to the main service. The subjects of the miniature illustrations (see miniature painting) were frequently derived from the appendix of the Psalter.
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. A few other sorts of manuscripts, such as the bestiarybestiary
, a type of medieval book that was widely popular, particularly from the 12th to 14th cent. The bestiary presumed to describe the animals of the world and to show what human traits they severally exemplify.
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, were, by tradition, profusely illustrated.

The Golden Age of Illumination

Paris was the birthplace of new ideas in book ornamentation at the beginning of the 13th cent. Picture and text were more closely integrated. The most striking quality of the Gothic miniatures was their parallel to stained glassstained glass,
in general, windows made of colored glass. To a large extent, the name is a misnomer, for staining is only one of the methods of coloring employed, and the best medieval glass made little use of it.
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 windows in the use of similar colors, drawing, and medallion frameworks. Book size decreased, initials were expanded, and grotesque little monsters and drolleries appeared in the margins.

Lay schools emerged in the 14th cent., directed by individual artists, such as Maître Honoré and Jean PucellePucelle, Jean
, c.1300–1355, French manuscript illuminator. Master of a celebrated workshop in Paris during the 1320s, Pucelle produced a masterpiece of illumination and a stylistic landmark in his Hours of Jeanne d'Évreux (c.1325; Cloisters, New York City).
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. Gold fields were replaced by colored and landscape backgrounds, although colors were sometimes abandoned for grisaillegrisaille
, a monochrome painting and drawing technique executed in tones of gray. Such works were often produced in the Renaissance to simulate sculpture, as in Uccello's equestrian portrait of Sir John Hawkswood (Cathedral of Florence).
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, as in the Hours of Jeanne d'Evreux (c.1325; Metropolitan Mus.) by Jean Pucelle.

Greater realism and a wealth of ornament in the margins can be seen in the works done in the early 15th cent. for the duc de Berry by the Burgundian court artists André Beauneveu, Jacquemart de HesdinHesdin, Jacquemart de
, fl. c.1384–1411, Franco-Flemish manuscript illuminator. Jacquemart illustrated numerous books of hours, including a number of manuscripts for Jean, duc de Berry.
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, and the Limbourg brothersLimbourg brothers
, fl. 1380–1416, family of Franco-Flemish manuscript illuminators. The Limbourg brothers, Pol, Jan, and Herman, were trained as goldsmiths. They succeeded Jacquemart de Hesdin in 1411 as court painters to Jean, duc de Berry.
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. The epitome of elegance was reached in the Très riches heures du duc de Berry (Chantilly) by the Limbourg brothers, showing a fusion of the refined Parisian style with the more realistic art of Flanders and also the influence of Italian panel painting.

Other notable works of the 15th cent. include the Hours of Catherine of Cleves (c.1428–45; Morgan Library) and illuminations of the Master of Mary of Burgundy (Bodleian, Oxford). The Boucicaut Master also made notable contributions. From the region of Tours came the highly accomplished Hours of Étienne Chevalier (Chantilly) by Jean FouquetFouquet or Foucquet, Jean or Jehan
, c.1420–c.1480, French painter and illuminator.
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 and the work of his pupil Jean Bourdichon. In England the early 14th-century art of illumination was nearly indistinguishable from that of France, e.g. Queen Mary's Psalter (British Mus.).

Italy was an important center of illumination in the 15th and 16th cent. Among those who worked as illuminators were Fra Angelico, Mantegna (briefly), Liberale da Verona, and Giulio Clovio. In general, illuminations were no longer closely related to the text but became little paintings in Renaissance frames. The decline of the art of the miniature was made inevitable by the invention of the printing press, and toward the end of the 15th cent. wood-block prints began to replace painted illumination.

Illumination in the Middle East and India

For information on the art of illumination in the Middle East and in India see Persian art and architecturePersian art and architecture,
works of art and structures produced in the region of Asia traditionally known as Persia and now called Iran. Bounded by fierce mountains and deserts, the high plateau of Iran has seen the flow of many migrations and the development of many
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; Islamic art and architectureIslamic art and architecture,
works of art and architecture created in countries where Islam has been dominant and embodying Muslim precepts in its themes. Background

In the century after the death (A.D.
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; Mughal art and architectureMughal art and architecture,
a characteristic Indo-Islamic-Persian style that flourished on the Indian subcontinent during the Mughal empire (1526–1857). This new style combined elements of Islamic art and architecture, which had been introduced to India during the Delhi
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; Indian art and architectureIndian art and architecture,
works of art and architecture produced on the Indian subcontinent, which is now divided among India, Pakistan, and Bangladesh. In the Western world, notable collections of Indian art can be seen in the British Museum, in the Victoria and Albert
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Since the mid-1960s many illuminated books have been published in relatively inexpensive facsimile editions. See S. Mitchell, Medieval Manuscript Painting (1965); D. Diringer, The Illuminated Book (rev. ed. 1967); D. M. Robb, The Art of the Illuminated Manuscript (1972); O. Pacht, Book Illumination in the Middle Ages (1987); J. J. G. Alexander, The Painted Page (1995); T. B. Husband, The Art of Illumination (museum catalog, 2009).



(or lighting), the illuminating of the surfaces of objects in order to make the objects visible or discernible to light-sensitive substances or devices. Man obtains most of his information about the outside world by means of sight, a fact that explains the importance of illumination. Illumination is also beneficial to a person’s general physiology, inducing a psychological state that is favorable for work or relaxation and is, therefore, of major importance to good health. Good illumination generally improves the productivity of labor (sometimes quite significantly, by 15 percent or more) and the quality of work and reduces occupational injuries and the incidence of traffic accidents.

The economics of improved illumination are such that in most cases the expenses are justified. Illumination that satisfies requirements of both health and economics is called rational. Health requirements are based on the study of the most important characteristics of human vision, such as visual acuity, sensitivity of the eye to contrast and color, rapidity of visual perception, and clarity of vision. In designing illumination for industrial premises or for workplaces, it is necessary to take into account the degree of precision required for the work, the contrast between the object that is to be discerned and the background, the necessity of discerning distant or rapidly moving details, the duration of the visual work, and, in a number of cases, the danger of traumatism. Illumination should provide a surface illuminance that is both adequate and uniform and a suitable distribution of brightness in the surrounding space. The light sources should be free of glare, the spectral composition of the light should be favorable, and the light beams should have a proper incident direction. The provision of rational illumination often presents complex problems in illumination engineering. Low-quality illumination can cause a variety of conditions or illnesses, such as myopia or accommodation spasms; it can also cause trauma, visual fatigue, or general fatigue. High-quality illumination creates favorable conditions for people.

Illumination can be natural, artificial, or mixed. Natural illumination is created by natural light sources and varies considerably, depending on such factors as the time of day and year, the geographic latitude of the locality, and atmospheric conditions. Natural illumination in open spaces produces the following illuminances on horizontal surfaces: 0.0005 lux for a moonless night, up to 0.2 lux in the light of a full moon, and up to 100,000 lux in direct sunlight.

A criterion used in evaluating natural illumination within buildings is the daylight factor. This factor is the percentage ratio of the illuminance at any point in the building to the illuminance measured at the same time on a horizontal platform outside the building when this platform is illuminated by the diffuse light of the whole sky. The magnitude of the daylight factor depends on the size and location of the light openings, the extent to which these openings transmit the light, the presence of external objects that have a screening effect, and the reflectivity of the interior surfaces of the room.

In the USSR, natural illumination within buildings is standardized. The purpose of the buildings and individual rooms is an important factor in establishing illumination standards. The basic standardized parameter is the daylight factor, which for industrial premises ranges from 0.25 to 10 percent. Natural illumination in buildings is provided by side windows or skylights or both. Natural illumination within buildings can be improved by a rational buildup of city blocks, by a correct orientation of buildings, by light-colored interior finishing of rooms, and by the use of double-casement windows. Rooms are protected from excessive direct sunlight by various means, for example, awnings and Venetian blinds. In many cases, engineering or economic considerations justify the construction of buildings without any natural illumination. Natural illumination may not be feasible for rooms where a constant temperature and humidity must be maintained, for rooms with high cleanliness requirements, and for rooms that require a rigidly specified illumination.

From a physiological point of view, natural illumination is the most favorable kind of illumination for humans. Sometimes, however, natural illumination is insufficient, and even in prehistoric times, man had a need for artificial illumination. In the past, artificial light sources included bonfires, torches, candles, and kerosine lamps. At the turn of the 20th century, electrical illumination became widespread and is now the main type of artificial lighting. In the USSR, the use of artificial illumination is regulated by standards. The basic quantitative standardized characteristic is the illuminance, which can range from 5 to 5,000 lux, depending on the purpose of the premises, the working conditions, and the type of work to be conducted.

The standardized criterion used in selecting artificial illumination for streets and squares is the mean brightness of the road surface. Existing standards also regulate the qualitative characteristics of artificial illumination. The standards require uniform illuminance of work surfaces, absence of fluctuations and abrupt changes of illuminance, and minimization or elimination of any visual discomfort or any blinding conditions that can arise if there is excessive brightness within the field of vision. Standards also require elimination of any undesirable glare from illuminated surfaces in the direction of the eye, a favorable spectral composition of the light, favorable conditions of shadowing, and sufficient brightness of all surrounding surfaces, including the ceilings and walls in rooms.

To satisfy these criteria, a rational illumination of industrial premises requires general illumination of the entire area. This general illumination is often supplemented by local illumination of the workplaces, resulting in combined illumination. The installation of local illumination without general illumination is prohibited. Emergency lighting is often provided in addition to the normal operational illumination; normal operational illumination provides rational illumination of industrial and public premises, whereas emergency lighting makes it possible to evacuate people or continue operations temporarily during failure of the normal operational illumination.

Incandescent lamps and gas-discharge devices are used as light sources for artificial illumination. Gas-discharge lamps are economical, have a long service life, and in many cases have replaced the incandescent lamps. Of the gas-discharge devices, it is the fluorescent lamp that provides the highest quality of illumination and that can successfully imitate natural illumination. Luminaires and projectors are used in order to achieve a rational utilization of the light energy provided by light sources, to protect the light sources from exposure to the environment, and to minimize glare.


Meshkov, V. V. Osnovy svetotekhniki, parts 1–2. Moscow-Leningrad, 1957–61. (Contains bibliography.)
Shaikevich, A. S. Kachestvo promyshlennogo osveshcheniia i putt ego povysheniia. Moscow-Leningrad, 1962. (Contains bibliography.)
Gusev, N. M., and N. N. Kireev. Osveshchenie promyshlennykh zdanii. Moscow, 1968. (Contains bibliography.)
Chernilovskaia, F. M. Osveshchenie promyshlennykh predpriiatii i ego gigienicheskoe znachenie. Leningrad, 1971.
Epaneshnikov, M. M. Elektricheskoe osveshchenie, 4th ed. Moscow, 1973.
Stroitel’nye normy i pravila, part 2, sec. A, Estestvennoe osveshchenie: Normy proektirovaniia. Moscow, 1973. Chapter 8. Stroitel’nye normy i pravila, part 2, sec. A, Iskusstvennoe osveshchenie: Normy proektirovaniia. Moscow, 1972. Chapter 9.



The geometric distribution of power reaching various parts of a dish reflector in an antenna system.
The power distribution to elements of an antenna array.
The science of the application of lighting.


The luminous flux density incident on a surface, i.e., the luminous flux per unit area; usually expressed in lumens per square foot or footcandles, and lumens per square meter or lux.


The lighting of a target by radar, laser, or other signals, so that it can be seen by a suitable detector in a missile or other weapon or by a sensor on the ground. This illumination provides guidance to weapons for its homing and destruction.
References in periodicals archive ?
This is seen as a small black dot in fundal retro-illumination (figure 5) and a white dot on the posterior capsular surface in direct illumination.
Note that in figure 10 (a), part of the cataract is seen in direct illumination with the cataract appearing white and part is seen in retro-illumination with the cataract appearing black.
Use of these complex wave modes helps to image areas with poor direct illumination and further improves steep-dip and event termination/truncation at salt boundaries.
and perimeter wall washers balance the flatness of the indirect lighting and allow for direct illumination tasks such as reading fine print in an otherwise darkened space.
Saving of direct illumination into the global lighting solutions provided by the photon and irradiance maps.

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