brightness

brightness

The intensity of light or other radiation emitted from – absolute or intrinsic brightness – or received from – apparent brightness – a celestial body, the latter decreasing as the distance from the body increases. Intrinsic brightness is directly related to the luminosity of a body in a given spectral region. Apparent brightness is considered in terms of apparent magnitude: a star one magnitude less than another is about 2.5 times brighter. If two stars belong to the main sequence then the brighter star is the hotter of the two. See also radio brightness.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Brightness

The amount of light energy reflected from a surface. The degree of brightness depends on the color value and texture on its surface. The surface brightness of a task should be the same as its background or brighter. The maximum brightness ratio should be 3:1, and the brightness between the task and the darkest background area should be 5:1 to avoid objectionable glare.

Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved

brightness

[′brīt·nəs]

(optics)

The characteristic of light that gives a visual sensation of more or less light.

luminance

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

brightness

That attribute of visual perception in accordance with which a surface appears to emit more light or less light. Now called luminance.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

Brightness

Alpha Centauri

brightest star in Centaurus constellation; closest star to Earth. [Astronomy: NCE, 74]

diamond

April birthstone, most reflective of gems. [Gem Symbolism: Jobes, 440–441]

North Star

bright star visible to naked eye and nearest to the north celestial pole. [Astronomy: EB, VIII: 79]

Sirius

dog star; brightest star in the heavens. [Astronomy: EB, IX: 238]

St. Elmo’s fire

glow of electrical discharge appearing on towers and ships’ masts. [Physics: EB, VIII: 780]

Venus

bright planet, second from the Sun. [Astronomy: EB, X: 392]

Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.

brightness

(graphics)

(Or "tone", "luminance", "value", "luminosity", "lightness") The coordinate in the HSB colour model that determines the total amount of light in the colour. Zero brightness is black and 100% is white, intermediate values are "light" or "dark" colours.

The other coordinates are hue and saturation.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

brightness

The black level of a display screen. Although it may sound peculiar, the brightness adjusts the "black level" of the display system (how black the black is). See contrast.

Copyright © 1981-2025 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Brightness

 

(also surface brightness), in astronomy, a characteristic of the emittance or reflectance of the surface of a celestial body. The brightness of faint celestial sources is expressed in terms of the number of stars of a given stellar magnitude in an area measuring 1 square second of arc (arcsec²), 1 square minute of arc (arcmin²), or 1 square degree (deg²). In other words, the illuminance from such an area is compared with the illuminance produced by a star of known stellar magnitude.

The brightness of the moonless night sky in clear weather, which is equal to 2 × 10^–8 stilbs (sb), is characterized by one star of stellar magnitude 22.4 per arcsec², or one star of stellar magnitude 4.61 per deg². The brightness of an average nebula is equal to one star of stellar magnitude 19–20 per arcsec². The brightness of Venus is equal to about one star of stellar magnitude 3 per arcsec². The brightness of an area of 1 arcsec² over which the light of a zero-magnitude star is distributed is equal to 9.25 sb. The brightness of the center of the solar disk is equal to 150,000 sb; that of the full moon, to 0.25 sb.

A surface for which the brightness does not depend on the angle of inclination of the area to the line of sight is said to be orthotropic. The flux emitted by such a surface behaves in accordance with Lambert’s law and is called the luminance. The unit of luminance is the lambert, which corresponds to a total flux of 1 lumen/cm².

D. IA. MARTYNOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.