Vi ([LAMBDA]) = 1.0 (250 [LESS THAN][LAMBDA] [LESS THAN]298 nm)
Vi ([LAMBDA]) = 1.00.094 (298 -[LAMBDA]) (298 [LESS THAN][LAMBDA] [LESS THAN]328 nanometers)
Vi ([LAMBDA]) = 1.00.015 (139 -[LAMBDA]) (328 [LESS THAN][LAMBDA] [LESS THAN]400 nanometers)
SPF value = the ratio of erythema effective exposure (Joules per square meter) (MED(PS)) to the erythema effective exposure (Joules per square meter) (MED(US)).
21 C.F.R. §352.73