What advantages does narrowband UVB have over broadband UVB?

Narrowband UVB utilizes a TL-01 light source emitting UV light almost exclusively at 311 nm, which is near the most effective action spectrum for induction of T-cell apoptosis in inflammatory skin diseases such as psoriasis. The absence of other wavelengths of UV light decreases side effects (erythema, carcinogenesis, photoaging) without sacrificing efficacy. Unlike broadband UVB, suberythemogenic doses are effective.