• Repeated exposures of 4 by 5-cm sites to erythemogenic doses (20 to 300 joules/sq cm) of long-wave ultraviolet light (UV-A; 320 to 400 nm) led to improvement of the psoriasis vulgaris condition in nine of ten patients treated. Comparison studies showed the therapeutic responses to be similar to that of daily sunburn spectrum (UV-B; 290 to 320 nm) radiation. This finding suggests that the therapeutic response spectrum for psoriasis may parallel the action spectrum for delayed erythema of all portions of the ultraviolet spectrum that pass through psoriatic scale.
(Arch Dermatol 113:1525-1528, 1977)
Parrish JA. Treatment of Psoriasis With Long-Wave Ultraviolet Light. Arch Dermatol. 1977;113(11):1525-1528. doi:10.1001/archderm.1977.01640110045005