“…While ultraviolet light combined with coal tar is a well-established treatment for psoriasis [19,20], in 1978, Petrozzi et al [21] showed UVB radiation alone to be almost as effective as crude coar tar combined with UVB. Initial use of UVB-only treatment was of a broadband variety, and both fluorescent and metal halide units were shown to be effective [22]. Work by Parrish and Jaenicke [23] suggested that limiting the spectrum of UVB therapy to the wavelengths between 296 and 313 nm would be more effective by limiting the wavelengths that either are erythrogenic without therapeutic value (<296 nm) or subtherapeutic (>313 nm).…”