"Narrowband" means a specific wavelength of ultraviolet (UV) radiation, 311 to 312 nm. The narrowband range of UV radiation is most beneficial component of natural sunlight for psoriasis. 

This is the most common form of phototherapy used for treating skin diseases like psoriasis, dermorgraphism, atopic eczema, vitiligo, pruritus, early cutaneous T-cell lymphoma, lichen planus and polymorphus light eruption. 

Advantages of Narrowband UVB compared to broadband UVB:

• Shorter treatment course.
• Shorter exposure times.
• Longer periods of remission before condition reappears
• Higher probability of success as it is more likely to clear the skin condition.