Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 Ultraviolet Light 231 that occur in both plants and animals. The relative effect of different wavelengths in producing the foregoing influences is shown in Fig. Although the curves differ very much from one another throughout most of the range, it is clear that in no instance is ultra- violet radiation effective at wavelengths longer than about 3100 A. 240 250 260 300 310 320 rriju 270 280 290 Wavelength Fig. Relation between wavelength in the ultraviolet region and the bac- tericidal, erythemic, a
Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 Ultraviolet Light 231 that occur in both plants and animals. The relative effect of different wavelengths in producing the foregoing influences is shown in Fig. Although the curves differ very much from one another throughout most of the range, it is clear that in no instance is ultra- violet radiation effective at wavelengths longer than about 3100 A. 240 250 260 300 310 320 rriju 270 280 290 Wavelength Fig. Relation between wavelength in the ultraviolet region and the bac- tericidal, erythemic, and antirachitic effects of ultraviolet radiation, together with the absorption of ergosterol. (Coblentz, 1939, Copyright, J. Am. Medical Assoc.) Under ordinary conditions no measurable radiation from the sun reaches the earth's surface at wavelengths shorter than 2950 A. It is clear then that under natural conditions the whole action of ultraviolet must occur between 3100 A and 2950 A. Under the best circum- stances solar radiation is extremely weak in this region, and when dust or smoke is abundant the shorter wavelengths are still further re-
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