This is a plot of the standard NASA data for the spectral irradiance of the solar disk in Watts/m2mm. The upper curve is formed by joining the data points for data outside the atmosphere. The lower curve is attributed to the Earth's surface under the condition described as "air mass 2". This designation corresponds to an angle of 60° between the zenith and the Sun. The data for the surface is from Brandhorst, et al.,Interim solar cell testing procedures for terrestrial applications, NASA Rep. TM X-71771 (Lewis Research Center) 1975. The points are actually calculated using the data from outside the atmosphere assuming a water content of 20 mmHg and ozone 3.4 mm Hg. The data for outside the atmosphere is from Thekaekara, M. P., Solar energy outside the earth's atmosphere, Solar Energy 14, 109 (1973).

 The iradiance outside the atmosphere can be compared with the blackbody curve at 6000K, a portion of which is reproduced at right. By examining the 400-700 nm nominal range of visible light, you can see that the solar irradiance is similar to that of a blackbody radiator. The curve at the surface is noticeably flatter, or more "white" if you take equal energy per wavelength as a definition of white.
 Wavelengthl(nm) Outsideatmosphere Surfacem=2 Wavelengthl(nm) Outsideatmosphere Surfacem=2 300 514 0 570 1712 1134 310 689 1 580 1715 1147 320 830 50 590 1700 1148 330 1059 105 600 1666 1135 340 1074 177 610 1635 1137 350 1093 217 620 1602 1137 360 1068 255 630 1570 1137 370 1181 320 640 1544 1141 380 1120 344 650 1511 1140 390 1098 371 660 1486 1136 400 1429 530 670 1456 1127 410 1751 693 680 1427 1119 420 1747 737 690 1402 1114 430 1639 737 700 1369 1102 440 1810 867 710 1344 1089 450 2006 1022 720 1314 1071 460 2066 1089 730 1290 1058 470 2033 1107 740 1260 1040 480 2074 1167 750 1235 1026 490 1950 1133 760 1211 660 500 1942 1165 770 1185 997 510 1882 1147 780 1159 981 520 1833 1136 790 1134 965 530 1842 1159 800 1109 950 540 1783 1140 810 1085 850 550 1725 1120 820 1060 900 560 1695 1111 830 1036 898
 Blackbody curve at 6000K
Index

Vision concepts

Color vision

Reference
Wyszecki & Stiles
Ch 1

 HyperPhysics***** Light and Vision R Nave
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