The Wavelength Question
If you are researching phototherapy for vitiligo or psoriasis, you have likely encountered two key numbers: 308nm and 311nm. Both are forms of ultraviolet B (UVB) light. Both are clinically proven. Both are recommended by dermatologists worldwide. So why two different wavelengths? Which one is actually "better"—and, more importantly, which one is better for you?

This article provides a data-driven, head-to-head comparison of 308nm excimer light and 311nm narrowband UVB. We will analyze peer-reviewed studies, examine efficacy and safety data, and help you understand why the answer is not about superiority, but about the right tool for the right job.

Feature	308nm Excimer (Laser/Lamp)	311nm Narrowband UVB
Primary Modality	Targeted phototherapy	Broadband or whole-body phototherapy
Ideal Candidate	Localized vitiligo/psoriasis (<10% BSA), difficult-to-reach areas	Widespread vitiligo/psoriasis (>10% BSA), generalized disease
Efficacy (Head-to-Head)	Equivalent – No statistically significant difference in repigmentation or clearance rates -2 -3 -8	Equivalent – Established first-line therapy with decades of evidence -1 -5
Cumulative UV Dose	Lower – Only lesions are treated	Higher – Healthy skin is also exposed
Treatment Sessions to Clear	Potentially fewer (accelerated protocols possible) -2	Typically more (15–40 sessions) -6
Side Effect Profile	Comparable; excimer lamp may have higher adverse event rate than laser -3	Well-tolerated; erythema most common
Cost	Higher initial investment (laser > lamp)	Lower equipment cost; higher long-term operational cost for clinics
Home Use Availability	Yes (FDA-cleared portable devices)	Yes (handheld NB-UVB units)

The Verdict: Neither wavelength is "better" in absolute terms. 308nm is superior for targeted, localized treatment. 311nm is the gold standard for widespread disease. They are complementary, not competitive.

308nm vs. 311nm UVB for Psoriasis and Vitiligo: Which Is Better?

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