The candela ( or ; symbol: cd ) is the SI base unit of luminous intensity ; that is, power emitted by a light source in a particular direction, weighted by the luminosity function ( a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function ).

A common candle emits light with a luminous intensity of roughly one candela.

Like other SI base units, the candela has an operational definition — it is defined by a description of a physical process that will produce one candela of luminous intensity.

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 hertz and that has a radiant intensity in that direction of watt per steradian.

Such a source could then be used to calibrate instruments designed to measure luminous intensity.

At other frequencies, more radiant intensity is required to achieve the same luminous intensity, according to the frequency response of the human eye.

where I < sub > v </ sub >( λ ) is the luminous intensity in candelas, I < sub > e </ sub >( λ ) is the radiant intensity in W / sr and is the standard luminosity function.

If more than one wavelength is present ( as is usually the case ), one must sum or integrate over the spectrum of wavelengths present to get the total luminous intensity.

A common candle emits light with roughly 1 cd luminous intensity.

The luminous intensity of light-emitting diodes is measured in millicandela ( mcd ), or thousandths of a candela.

Prior to 1948, various standards for luminous intensity were in use in a number of countries.

The candela is the luminous intensity, in the perpendicular direction, of a surface of 1 / 600 000 square metre of a black body at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre.

If a source emits a known luminous intensity I < sub > v </ sub > ( in candelas ) in a well-defined cone, the total luminous flux Φ < sub > v </ sub > in lumens is given by

Category: Units of luminous intensity

* centicandela ( ccd ), an SI unit of luminous intensity denoting one hundredth of a candela.

The conventional SI system of units is based on seven basic dimensional quantities, namely distance, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction.

* candela for luminous intensity

Although they are at temperatures of roughly, the contrast with the surrounding material at about 5780 K ( 5500 ° C ) leaves them clearly visible as dark spots, as the luminous intensity of a heated black body ( closely approximated by the photosphere ) is a function of temperature to the fourth power.

The luminous gain of the discussed tube was calculated from Eq. ( 6 ) for the 16 possible combinations of S-11 and S-20 photocathodes and P-11 and P-20 phosphor screens, for night light and P-20 light input.

# Luminous: The third bhūmi is named " luminous ", because, for a bodhisattva who accomplishes this bhūmi, the light of Dharma is said to radiate for others from the bodhisattva.

CD sleeves for H. luminous were silk-screened and printed by the band using 100 % post-consumer recycled cardboard.

Dark matter's existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation, and was originally hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and calculations based on the mass of the visible " luminous " matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium.

" Its brilliant flares were clearly visible for great distances at sea, and at night its glowing lava turned it into a brilliant luminous cone.

In 1798 he painted luminous and airy scenes for the pendentives and cupula of the Real Ermita ( Chapel ) of San Antonio de la Florida in Madrid.

* 1997 – GRB 970228, a highly luminous flash of gamma rays, strikes the Earth for 80 seconds, providing early evidence that gamma-ray bursts occur well beyond the Milky Way.

They relate to raw power by a quantity called luminous efficacy, and are used for purposes like determining how to best achieve sufficient illumination for various tasks in indoor and outdoor settings.

Practical applications exist only for chemical compounds of promethium-147, which are used in luminous paint, atomic batteries and thickness measurement devices, even though promethium-145 is the most stable promethium isotope.

Shakespeare was also noted for his frequent play with less serious puns, the " quibbles " of the sort that made Samuel Johnson complain, " A quibble is to Shakespeare what luminous vapours are to the traveller!

Bramante's work in the city, which included Santa Maria presso San Satiro ( a reconstruction of a small 9th-century church ), the beautiful luminous tribune of Santa Maria delle Grazie and three cloisters for Sant ' Ambrogio, drew also on his studies of the Early Christian architecture of Milan such as the Basilica of San Lorenzo.

Based on measurements of a taper-type, paraffin wax candle, a modern candle typically burns at a steady rate of about 0. 1 g / min, releasing heat at roughly 80 W. The light produced is about 13 lumens, for a luminous efficacy of about 0. 16 lumens per watt ( luminous efficacy of a source )-almost a hundred times lower than an incandescent light bulb.

New developments over the past few years include the recognition of short gamma-ray bursts as a separate class ( likely due to merging neutron stars and not associated with supernovae ), the discovery of extended, erratic flaring activity at X-ray wavelengths lasting for many minutes after most GRBs, and the discovery of the most luminous ( GRB 080319B ) and the former most distant ( GRB 090423 ) objects in the universe.

* 2009: Holland Cotter of The New York Times, " for his wide ranging reviews of art, from Manhattan to China, marked by acute observation, luminous writing and dramatic storytelling.

Since quartz is very strong, the gas pressure can be higher, which reduces the rate of evaporation of the filament, permitting it to run a higher temperature ( and so luminous efficacy ) for the same average life.

With the help of some companies such as Philips and Osram Sylvania, halogen bulbs have been made for standard household fittings, and can replace banned incandescent light bulbs of low luminous efficacy.

Garbo was nominated four times for an Academy Award and received an honorary one in 1954 for her " luminous and unforgettable screen performances ".

They were climbing the hill in the night when the headlights abruptly probed solid blackness, became two parallel luminous tubes which broadened out into a faint mist of light and ended.

The luminous efficiency Af of a photocathode depends on the maximum radiant sensitivity Af and on the spectral distribution of the incident light Af by the relation: Af where Af is normalized radiant photocathode sensitivity.

The course of the rays in the meridional section is no longer symmetrical to the principal ray of the pencil ; and on an intercepting plane there appears, instead of a luminous point, a patch of light, not symmetrical about a point, and often exhibiting a resemblance to a comet having its tail directed towards or away from the axis.

It is at least 110 times visually more luminous than the Sun, but this underestimates its strength as much of the " light " it gives off is in the infrared ; total ( bolometric ) power output is about 180 times that of the Sun.

It forms a slightly more luminous, oval glow directly opposite the Sun within the band of luminous zodiacal light.

Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.

In February 2008, a luminous efficacy of 300 lumens of visible light per watt of radiation ( not per electrical watt ) and warm-light emission was achieved by using nanocrystals.

Similar nebulae not illuminated by stars do not exhibit visible radiation, but may be detected as opaque clouds blocking light from luminous objects behind them ; they are called " dark nebulae ".

Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

The Chandra X-ray Observatory | Chandra X-ray image is of the quasar PKS 1127-145, a highly luminous source of X-rays and visible light about 10 billion light years from Earth.

:" The zodiacal light is nothing but the solar atmosphere, a rare and subtile fluid, either luminous by itself, or made so by the rays of the sun surrounding its globe ; but in a greater quantity, and more extensively, about its equator, than any other.