Phototherapy lamps emit light energy. Narrowband UVB phototherapy (NB-UVB) light comprises a subset of the UVB spectrum centered at roughly 311 nm.  Studies have shown that

• Without medication, only 4% of the sun's rays help to improve skin disease.  The balance of the sun's rays merely tan or burn the skin leading to other long-term skin problems.
• Narrow band UVB uses the optimal part of the UV light spectrum which slows growth of psoriasis lesions or re-pigmentation of one's natural skin coloring.
• Exposure time of narrowband UVB can be longer than with traditional broadband UVB yielding more effective results.  Recent studies have shown 75% clearing (PASI 75) with narrowband UVB.
• Erythemal response (similar to sunburn) is nearly eliminated with narrowband UVB light.
• Risks and side effects of other treatments such as systemic drugs have not been found with narrowband UVB light.