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Radiance

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is also conserved. In real systems, the étendue may increase (for example due to scattering) or the radiant flux may decrease (for example due to absorption) and, therefore, basic radiance may decrease. However, étendue may not decrease and radiant flux may not increase and, therefore, basic radiance
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Radiance is useful because it indicates how much of the power emitted, reflected, transmitted or received by a surface will be received by an optical system looking at that surface from a specified angle of view. In this case, the solid angle of interest is the solid angle subtended by the optical
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refers to an area on the surface of the detector and Ω to the solid angle subtended by the source as viewed from that detector. When radiance is conserved, as discussed above, the radiance emitted by a source is the same as that received by a detector observing it.
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Spectral radiance expresses radiance as a function of frequency or wavelength. Radiance is the integral of the spectral radiance over all frequencies or wavelengths. For radiation emitted by the surface of an ideal
200:, so that its radiance is uniform with respect to angle of view, and is simply the Stefan–Boltzmann integral divided by π. This factor is obtained from the solid angle 2π steradians of a hemisphere decreased by 237: 1767:
per unit frequency or wavelength. The latter is commonly measured in W⋅m⋅nm. "Spectral emittance" is an old term for this quantity. This is sometimes also confusingly called "spectral intensity".
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are good indicators of how bright an object will appear. For this reason, radiance and luminance are both sometimes called "brightness". This usage is now discouraged (see the article
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equal to the input, unless the index of refraction changes. As an example, if you form a demagnified image with a lens, the optical power is concentrated into a smaller area, so the
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Historically, radiance was called "intensity" and spectral radiance was called "specific intensity". Many fields still use this nomenclature. It is especially dominant in
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is higher at the image. The light at the image plane, however, fills a larger solid angle so the radiance comes out to be the same assuming there is no loss at the lens.
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per unit area. This is the emitted component of radiosity. "Radiant emittance" is an old term for this quantity. This is sometimes also confusingly called "intensity".
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refers to an area on the surface of the source, and Ω to the solid angle into which the light is emitted. When calculating radiance received by a detector,
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per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include
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per unit frequency or wavelength. The latter is commonly measured in W⋅m⋅nm. This is sometimes also confusingly called "spectral intensity".
912: 168:. This means that for an ideal optical system in air, the radiance at the output is the same as the input radiance. This is sometimes called 231:("e" for "energetic", to avoid confusion with photometric quantities, and "Ω" to indicate this is a directional quantity), is defined as 201: 1072:
Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called "radiant power", and called
326:{\displaystyle L_{\mathrm {e} ,\Omega }={\frac {\partial ^{2}\Phi _{\mathrm {e} }}{\partial \Omega \,\partial (A\cos \theta )}},} 1886:
per unit frequency or wavelength. The latter is commonly measured in J⋅m⋅nm. This is sometimes also called "spectral fluence".
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As the light travels through an ideal optical system, both the étendue and the radiant flux are conserved. Therefore,
2148: 905: 661:{\displaystyle L_{\mathrm {e} ,\Omega ,\lambda }={\frac {\partial L_{\mathrm {e} ,\Omega }}{\partial \lambda }},} 94: 55: 2215: 898: 192:, while the integral of its radiance, over the hemisphere into which its surface radiates, is given by the 1245:
Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr⋅nm. This is a
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for a discussion). The nonstandard usage of "brightness" for "radiance" persists in some fields, notably
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quantity: the radiance of a surface depends on the direction from which it is being observed.
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should be denoted with suffix "e" (for "energetic") to avoid confusion with photometric or
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per unit frequency or wavelength. The latter is commonly measured in W⋅sr⋅m⋅nm. This is a
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Radiant flux emitted, reflected, transmitted or received, per unit solid angle. This is a
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Radiant flux per unit frequency or wavelength. The latter is commonly measured in W⋅nm.
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integrated over time of irradiation. This is sometimes also called "radiant fluence".
869:{\displaystyle L_{\mathrm {e} ,\Omega }^{*}={\frac {L_{\mathrm {e} ,\Omega }}{n^{2}}}} 2181: 1962: 1331: 1208: 1159: 455: 82: 1849: 1806: 1730: 1687: 781: 165: 1514: 189: 953: 138: 42:
per unit projected area. Radiance is used to characterize diffuse emission and
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quantity. This is sometimes also confusingly called "spectral intensity".
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emitted, reflected, transmitted or received by a given surface, per unit
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per unit area. This is sometimes also confusingly called "intensity".
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per unit area. This is sometimes also confusingly called "intensity".
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quantity. This is sometimes also confusingly called "intensity".
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Radiant flux emitted, reflected, transmitted or received by a
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The radiance divided by the index of refraction squared is
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International Lighting in Controlled Environments Workshop
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at a given temperature, spectral radiance is governed by
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is taken as a function of frequency or of wavelength.
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Comparison of photometric and radiometric quantities
2087: 2085: 437:When calculating the radiance emitted by a source, 868: 762: 660: 551: 325: 2050: 678: 434:is isotropic (independent of viewing direction). 387:is a function of viewing direction, depending on 2207: 2091:Directional quantities are denoted with suffix " 2082: 2029: 2027: 2025: 2023: 2021: 2019: 2017: 2143: 2141: 2139: 1840:per unit area, or equivalently irradiance of a 1392:watt per steradian per square metre, per metre 202:integration over the cosine of the zenith angle 1351:watt per steradian per square metre per hertz 145:is an optical system, radiance and its cousin 2014: 906: 2136: 1952: 355:emitted, reflected, transmitted or received; 207: 1602:(emitted, reflected and transmitted by) a 913: 899: 2178:Introduction to Radiometry and Photometry 295: 112:. "Intensity" has many other meanings in 127: 2208: 883: 85:is the radiance of a surface per unit 1848: 1729: 1610: 1459: 1330: 1207: 1080: 991:Energy of electromagnetic radiation. 933: 930: 927: 924: 1987:Alternative symbols sometimes seen: 1303:watt per steradian per square metre 683:Radiance of a surface is related to 449: 2069:Spectral quantities given per unit 2033:Spectral quantities given per unit 13: 1904:joule per square metre, per metre 849: 842: 821: 814: 784:in which that surface is immersed; 748: 740: 735: 731: 710: 703: 646: 639: 632: 623: 606: 599: 537: 530: 523: 514: 497: 490: 296: 292: 289: 281: 276: 266: 254: 247: 14: 2232: 2194: 2180:, Artech House, Boston, MA, 1994 1867:joule per square metre per hertz 1785:watt per square metre, per metre 1666:watt per square metre, per metre 1547:watt per square metre, per metre 790:is the étendue of the light beam. 1748:watt per square metre per hertz 1629:watt per square metre per hertz 1482:watt per square metre per hertz 1030:Radiant energy per unit volume. 570:Spectral radiance in wavelength 16:Physical quantity in radiometry 2170: 679:Conservation of basic radiance 461:Spectral radiance in frequency 314: 299: 123: 50:, and to quantify emission of 1: 2129: 1836:Radiant energy received by a 1267:watt per steradian per metre 1226:watt per steradian per hertz 116:, with the most common being 407:. For the special case of a 7: 2102: 1961:recommend that radiometric 212: 93:, depending on whether the 10: 2239: 453: 18: 2073:are denoted with suffix " 2037:are denoted with suffix " 1924: 1881: 1805: 1762: 1686: 1643: 1567: 1496: 1412: 1365: 1287: 1244: 1158: 1121: 1034: 995: 952: 947: 944: 941: 938: 54:and other particles. The 48:electromagnetic radiation 21:Radiance (disambiguation) 208:Mathematical definitions 170:conservation of radiance 2176:William Ross McCluney, 2119:Sakuma–Hattori equation 1959:Standards organizations 1821:joule per square metre 423:is proportional to cos 1882:Radiant exposure of a 1763:Radiant exitance of a 1702:watt per square metre 1583:watt per square metre 1432:watt per square metre 1011:joule per cubic metre 997:Radiant energy density 870: 764: 662: 553: 327: 133: 2124:Wien displacement law 2011:for radiant exitance. 1465:Spectral flux density 871: 765: 663: 554: 328: 131: 81:The related quantity 1995:for radiant energy, 805: 694: 590: 481: 238: 194:Stefan–Boltzmann law 19:For other uses, see 2216:Physical quantities 1461:Spectral irradiance 1335:Specific intensity 921: 893:SI radiometry units 884:SI radiometry units 830: 675:is the wavelength. 118:power per unit area 58:of radiance is the 2003:for radiant flux, 1612:Spectral radiosity 1209:Spectral intensity 890: 880:may not increase. 866: 808: 760: 658: 566:is the frequency. 549: 409:Lambertian surface 342:partial derivative 323: 134: 1948: 1947: 1850:Spectral exposure 1731:Spectral exitance 1332:Spectral radiance 1160:Radiant intensity 864: 755: 653: 544: 456:Spectral radiance 450:Spectral radiance 318: 196:. Its surface is 83:spectral radiance 2228: 2188: 2174: 2168: 2167: 2165: 2164: 2145: 2096: 2089: 2080: 2067: 2048: 2043:" (Greek letter 2031: 2012: 2010: 2007:for irradiance, 2006: 2002: 1998: 1994: 1990: 1985: 1970: 1956: 1901: 1864: 1818: 1807:Radiant exposure 1782: 1745: 1699: 1688:Radiant exitance 1663: 1626: 1580: 1544: 1528: 1524: 1520: 1512: 1508: 1497:Irradiance of a 1479: 1429: 1389: 1348: 1300: 1264: 1223: 1171: 1135: 1094: 1045: 1008: 965: 922: 915: 908: 901: 894: 889: 875: 873: 872: 867: 865: 863: 862: 853: 852: 845: 835: 829: 824: 817: 782:refractive index 769: 767: 766: 761: 756: 754: 746: 745: 744: 743: 729: 727: 726: 714: 713: 706: 667: 665: 664: 659: 654: 652: 644: 643: 642: 635: 621: 616: 615: 602: 583:, is defined as 558: 556: 555: 550: 545: 543: 535: 534: 533: 526: 512: 507: 506: 493: 474:, is defined as 422: 406: 332: 330: 329: 324: 319: 317: 287: 286: 285: 284: 274: 273: 263: 258: 257: 250: 166:geometric optics 73: 2238: 2237: 2231: 2230: 2229: 2227: 2226: 2225: 2206: 2205: 2197: 2192: 2191: 2175: 2171: 2162: 2160: 2159:catalogue. 1989 2147: 2146: 2137: 2132: 2105: 2100: 2099: 2090: 2083: 2068: 2051: 2032: 2015: 2008: 2004: 2000: 1996: 1992: 1988: 1986: 1973: 1957: 1953: 1944: 1900: 1891: 1863: 1854: 1817: 1811: 1781: 1772: 1744: 1735: 1698: 1692: 1662: 1653: 1644:Radiosity of a 1625: 1616: 1579: 1573: 1543: 1534: 1526: 1522: 1518: 1515:solar flux unit 1510: 1506: 1478: 1469: 1463: 1428: 1422: 1416: 1388: 1379: 1347: 1338: 1334: 1299: 1293: 1263: 1254: 1222: 1213: 1170: 1164: 1138:watt per metre 1134: 1127: 1093: 1086: 1044: 1040: 1007: 1001: 964: 958: 920: 919: 892: 886: 858: 854: 841: 840: 836: 834: 825: 813: 812: 806: 803: 802: 747: 739: 738: 734: 730: 728: 722: 718: 702: 701: 697: 695: 692: 691: 681: 645: 631: 630: 626: 622: 620: 598: 597: 593: 591: 588: 587: 582: 536: 522: 521: 517: 513: 511: 489: 488: 484: 482: 479: 478: 473: 458: 452: 433: 416: 412: 404: 400: 386: 350: 288: 280: 279: 275: 269: 265: 264: 262: 246: 245: 241: 239: 236: 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Retrieved 2152: 2074: 2038: 1954: 1918: 1914: 1910: 1897: 1892: 1883: 1877: 1873: 1860: 1855: 1841: 1837: 1831: 1827: 1812: 1799: 1795: 1791: 1778: 1773: 1764: 1758: 1754: 1741: 1736: 1722: 1718: 1712: 1708: 1693: 1680: 1676: 1672: 1659: 1654: 1645: 1639: 1635: 1622: 1617: 1603: 1599: 1593: 1589: 1574: 1561: 1557: 1553: 1540: 1535: 1498: 1492: 1488: 1475: 1470: 1452: 1448: 1442: 1438: 1423: 1418:Flux density 1406: 1402: 1398: 1385: 1380: 1371: 1367: 1361: 1357: 1344: 1339: 1323: 1319: 1313: 1309: 1294: 1288: 1281: 1277: 1273: 1260: 1255: 1246: 1240: 1236: 1232: 1219: 1214: 1200: 1194: 1190: 1186: 1165: 1152: 1148: 1144: 1131: 1117: 1113: 1109: 1090: 1067: 1063: 1059: 1036:Radiant flux 1025: 1021: 1017: 1002: 986: 982: 978: 959: 887: 878: 795: 793: 787: 777: 772: 682: 672: 670: 577: 573: 569: 568: 563: 561: 468: 464: 460: 459: 442: 438: 436: 428: 424: 418: 392: 391:through cos 388: 381: 379: 373: 369: 365: 353:radiant flux 335: 225: 221: 217: 216: 190:Planck's law 182: 173: 169: 159: 141:. Since the 135: 106:astrophysics 99: 80: 75: 68:square metre 36:radiant flux 31: 25: 2114:Light field 1969:quantities. 1372:directional 1324:directional 1247:directional 1201:directional 798:defined by 380:In general 360:solid angle 124:Description 76:directional 74:). It is a 40:solid angle 2221:Radiometry 2210:Categories 2163:2015-03-15 2130:References 2071:wavelength 1963:quantities 1940:Photometry 1935:Radiometry 1925:See also: 1527:10 Jy 1519:1 sfu 1414:Irradiance 1354:W⋅sr⋅m⋅Hz 1249:quantity. 1203:quantity. 1074:luminosity 931:Dimension 576:, denoted 467:, denoted 224:, denoted 198:Lambertian 186:black body 178:irradiance 151:Brightness 91:wavelength 44:reflection 28:radiometry 2035:frequency 1569:Radiosity 1507:1 Jy 1176:steradian 1174:watt per 1097:watt per 925:Quantity 850:Ω 827:∗ 822:Ω 749:∂ 736:Φ 732:∂ 711:Ω 650:λ 647:∂ 640:Ω 624:∂ 613:λ 607:Ω 541:ν 538:∂ 531:Ω 515:∂ 504:ν 498:Ω 374:projected 358:Ω is the 340:∂ is the 312:θ 309:⁡ 297:∂ 293:Ω 290:∂ 277:Φ 267:∂ 255:Ω 162:invariant 147:luminance 137:system's 110:astronomy 87:frequency 64:steradian 52:neutrinos 2103:See also 1449:received 1289:Radiance 1229:W⋅sr⋅Hz 399:through 218:Radiance 213:Radiance 95:spectrum 32:radiance 2109:Étendue 1884:surface 1870:J⋅m⋅Hz 1842:surface 1838:surface 1765:surface 1751:W⋅m⋅Hz 1723:surface 1719:emitted 1646:surface 1632:W⋅m⋅Hz 1604:surface 1600:leaving 1499:surface 1485:W⋅m⋅Hz 1453:surface 1395:W⋅sr⋅m 1368:surface 1320:surface 1306:W⋅sr⋅m 1270:W⋅sr⋅m 948:Symbol 942:Symbol 780:is the 685:étendue 574:surface 465:surface 372:is the 351:is the 344:symbol; 222:surface 174:at most 114:physics 56:SI unit 34:is the 2184:  1967:photon 1513:) and 1503:jansky 1056:= J/s 934:Notes 773:where 671:where 562:where 427:, and 417:/(∂Ω ∂ 336:where 72:W·sr·m 1721:by a 1451:by a 1099:hertz 969:joule 945:Name 939:Name 928:Unit 581:e,Ω,λ 572:of a 472:e,Ω,ν 463:of a 376:area. 220:of a 2182:ISBN 1907:J/m 1824:J/m 1788:W/m 1705:W/m 1669:W/m 1586:W/m 1550:W/m 1435:W/m 1384:e,Ω, 1343:e,Ω, 1259:e,Ω, 1218:e,Ω, 1141:W/m 1049:watt 1014:J/m 395:and 368:cos 108:and 66:per 62:per 60:watt 2157:ISO 1999:or 1991:or 1529:). 1298:e,Ω 1169:e,Ω 687:by 432:e,Ω 405:/∂Ω 385:e,Ω 306:cos 229:e,Ω 164:in 143:eye 89:or 46:of 26:In 2212:: 2155:. 2151:. 2138:^ 2095:". 2084:^ 2079:". 2052:^ 2045:nu 2016:^ 1974:^ 1930:SI 1896:e, 1859:e, 1777:e, 1740:e, 1658:e, 1621:e, 1539:e, 1525:= 1521:= 1509:= 1474:e, 1182:sr 1180:W/ 1130:e, 1105:Hz 1103:W/ 1089:e, 413:∂Φ 411:, 401:∂Φ 204:. 157:. 120:. 104:, 30:, 2166:. 2093:Ω 2076:λ 2040:ν 2009:W 2005:I 2001:F 1997:P 1993:E 1989:W 1919:T 1917:⋅ 1915:L 1913:⋅ 1911:M 1898:λ 1893:H 1878:T 1876:⋅ 1874:M 1861:ν 1856:H 1832:T 1830:⋅ 1828:M 1816:e 1813:H 1800:T 1798:⋅ 1796:L 1794:⋅ 1792:M 1779:λ 1774:M 1759:T 1757:⋅ 1755:M 1742:ν 1737:M 1713:T 1711:⋅ 1709:M 1697:e 1694:M 1681:T 1679:⋅ 1677:L 1675:⋅ 1673:M 1660:λ 1655:J 1640:T 1638:⋅ 1636:M 1623:ν 1618:J 1594:T 1592:⋅ 1590:M 1578:e 1575:J 1562:T 1560:⋅ 1558:L 1556:⋅ 1554:M 1541:λ 1536:E 1517:( 1505:( 1493:T 1491:⋅ 1489:M 1476:ν 1471:E 1443:T 1441:⋅ 1439:M 1427:e 1424:E 1407:T 1405:⋅ 1403:L 1401:⋅ 1399:M 1386:λ 1381:L 1362:T 1360:⋅ 1358:M 1345:ν 1340:L 1314:T 1312:⋅ 1310:M 1295:L 1282:T 1280:⋅ 1278:L 1276:⋅ 1274:M 1261:λ 1256:I 1241:T 1239:⋅ 1237:L 1235:⋅ 1233:M 1220:ν 1215:I 1195:T 1193:⋅ 1191:L 1189:⋅ 1187:M 1166:I 1153:T 1151:⋅ 1149:L 1147:⋅ 1145:M 1132:λ 1128:Φ 1118:T 1116:⋅ 1114:L 1112:⋅ 1110:M 1091:ν 1087:Φ 1068:T 1066:⋅ 1064:L 1062:⋅ 1060:M 1054:W 1043:e 1041:Φ 1026:T 1024:⋅ 1022:L 1020:⋅ 1018:M 1006:e 1003:w 987:T 985:⋅ 983:L 981:⋅ 979:M 974:J 963:e 960:Q 914:e 907:t 900:v 860:2 856:n 847:, 843:e 838:L 832:= 819:, 815:e 810:L 788:G 778:n 758:, 752:G 741:e 724:2 720:n 716:= 708:, 704:e 699:L 673:λ 656:, 637:, 633:e 628:L 618:= 610:, 604:, 600:e 595:L 578:L 564:ν 547:, 528:, 524:e 519:L 509:= 501:, 495:, 491:e 486:L 469:L 443:A 439:A 429:L 425:θ 421:) 419:A 415:e 403:e 393:θ 389:θ 382:L 370:θ 366:A 362:; 349:e 347:Φ 321:, 315:) 303:A 300:( 282:e 271:2 260:= 252:, 248:e 243:L 226:L 70:( 23:.

Index

Radiance (disambiguation)
radiometry
radiant flux
solid angle
reflection
electromagnetic radiation
neutrinos
SI unit
watt
steradian
square metre
spectral radiance
frequency
wavelength
spectrum
heat transfer
astrophysics
astronomy
physics
power per unit area

entrance pupil
eye
luminance
Brightness
laser physics
invariant
geometric optics
irradiance
black body

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