and Kalanchoe are from 3 to 200 times less sensitive to nighttime light than Xanthium. It is known that brief flashes of light applied during the dark period will affect the flowering process. In Xanthium flashes of very high intensity light of less than 1 second can inhibit flowering; however, the available evidence shows that even the irradiance in the worst case geometry (o.4 W/m ) is insufficient to influence flowering. CONCLUSIONS The available evidence indicates that ground irradiance from SPS will not affect the growth or development of plants. During daylight hours, the effect of specular radiation is unlikely to influence the aerial parts of plants since these show no sensitivity to insolation. Developmental effects of either specular or diffuse radiation are unlikely to occur either during day- or nighttime irradiation. Although plants are sensitive to low intensity radiation, the duration of the irradiation provided by reflection from SPS are insufficient to cause developmental changes. LITERATURE CITED 1. Space Power System Brightness Due to Reflected Sunlight. Final Report. Boeing Aerospace Company Document D 180-25923-1 (1980). 2. Salisbury, F.B. The Flowering Process. MacMillan Co. New York (1963). 3. Hillman, W. S. The Physiology of Phytochrome. Ann. Rev. Plant Physiol. 18, 301-324 (1967).
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