2 -1 where L is radiance (W/cm X sr ) and is the action spectrum of photo chemical injury to monkey eyes determined by Ham et al (ref. 8), whose values are shown in Table I. Maximum permissible exposure may be calculated as: The highest solar irradiance values which we could locate were obtained by measuring summer sunlight near the zenith in California. They are shown as the top curve in Figure 1. We have integrated these values, obtaining a total irradiance value of: When we integrate the same values with the function of Table I, we obtain maximum blue irradiance on earth from sunlight of: and A is the area of the Sun. Thus, the maximum safe viewing time of the sun from the latitude of California at noon in the summer is
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