4Ut) KADIATION IJIOLOGY 



Crete monochronriMt ic lines. I"'(>r any j:;i\('n line of wave len{i;th X, 



Qx = It (13-3) 



wluMC / is the incident intensity ul' the line and / the duration of the 

 exposure.'^ The total incident energy from the mercury arc within the 

 limits of the erythemal spectrum may be ol)tained hy summing the 

 amounts of energy delivered by the individual lines and multij^lying by /: 



Q = ({f^ + /o + • • • + A) (13-4) 



where l\, I-i, . . . , li are the intensities of the \arious lines. 



In Fig. 13-36 the "erythemal effective intensity" of the lines is indi- 

 cated. This is obtained bj- multiplying the intensity of each line by the 



Table 13-1. Erythemal Threshold in Ter.ms of "Erythemal 



ICffective Energy"" 



(Blum and Terus, 194()a.) 



" See Fig. 13-3a and b. 



erythemal sensitivity S for that wave length relative to the maximum in 

 the erythemal spectrum at 0.2967 /x (see Fig. 13-3a; the relative sensitivity 

 is, of course, measured in terms of the reciprocal of the threshold). We 

 may then express the "erythemal effective energy" Q' as 



Q' = til.S, + I,S, + • • • + liSi). (13-5) 



This is a measure which has been variously employed. Let us accept it as 

 an approximation which can be put to test. In Fig. 13-3 are shown 

 spectra of the mercury arc when restricted with spectral filters, and also 

 the intensity of a low-pressure mercury arc which delivers practically all 

 its radiation in the 0.2537-/i line. In an experiment carried out by Blum 



>•' It is understood that the values of Q and / are referred to unit area of the skin 

 upon which they impinge, but for brevity of discussion this will not be specifically 

 stated in each case. 



