Narrowband UVB (311 nm) is the workhorse for widespread disease; targeted 308 nm therapy is the precision tool for limited, stubborn lesions. Most of the time, the right choice comes down to how much skin is involved, where it is, and how the disease is behaving.
You see it every week in OPD. A patient with vitiligo on both hands and one patch on the face. Another with psoriasis that has cleared everywhere except the scalp and soles. A parent asking whether the light treatment their relative used will work for their child's eczema. Each time, you are deciding not just whether to use phototherapy, but which wavelength will get this patient the best result with the least UV exposure and the fewest visits.
Why the choice is harder than it looks
The two wavelengths are only 3 nm apart, but they are delivered very differently, and the terminology around them has become muddled.
Labels overlap. "Excimer" is now used loosely for any 308 nm device, including LED sources that match the wavelength but not the light source behind most of the published evidence.
Patients arrive with expectations. Many have read that 308 nm is "newer" or "stronger" and ask for it by name, even when their disease is too widespread for a targeted device.
Practical limits are real. Clinic NB-UVB means two to three visits a week for months, which many working patients and students cannot sustain. Targeted devices treat only what you aim them at.
The cost of getting it wrong falls on the patient: more visits, more cumulative UV, slower results, and a higher chance they give up before treatment has had time to work.
The two tools at a glance
Both wavelengths act the same way at the cellular level: UVB calms the local immune response and, in vitiligo, stimulates the remaining melanocytes. The difference is in how the light reaches the skin.
Narrowband UVB (311 nm) | Targeted 308 nm | |
Light sources | Fluorescent tubes (cabins, panels, hand-held lamps and wands) | Xenon-chloride excimer laser or lamp; also 308 nm LED devices |
What it treats | A whole region or the whole body at once | Only the lesions you aim it at |
Healthy skin exposed | Yes, across the treated area | Little or none |
Dose per session | Lower, built up gradually | Higher doses possible on lesions alone |
Best fit | Widespread or spreading disease | Limited, localised or resistant lesions |
Typical schedule | 2–3 sessions a week | Usually 1–2 sessions a week |
A note on 308 nm sources. Most of the clinical evidence for targeted 308 nm therapy comes from excimer lasers and lamps. 308 nm LED devices match the wavelength, but they have a smaller evidence base of their own. When you read a study or a product claim, check which source was used.
Vitiligo: choose by extent and activity
For vitiligo, the two wavelengths repigment equally well; extent decides which one to use. A 2016 meta-analysis of six randomised trials found that excimer lamps, excimer laser and NB-UVB are all safe and effective, with no significant difference in repigmentation. A 2022 review in the Journal of the European Academy of Dermatology and Venereology recommends keeping NB-UVB for patients with more than 5–10% body surface area involved.
Clinical picture | First choice | Why |
More than 5–10% BSA, or several body regions | NB-UVB (311 nm) | Treats everything at once; practical for widespread disease |
Active or spreading disease | NB-UVB (311 nm) | Treats new and subclinical patches as well as visible ones |
Stable, localised disease under 5–10% BSA | Targeted 308 nm | Spares normal skin; lower cumulative dose |
Face and neck | Targeted 308 nm | High-responding sites; precise treatment around eyes and lips |
Hands, feet, bony areas | Targeted 308 nm with a topical calcineurin inhibitor | Resistant sites; targeted devices allow higher lesional doses, and adding tacrolimus improves results |
Widespread disease with a few stubborn patches | NB-UVB, plus targeted 308 nm on resistant patches | Combines coverage with a focused boost |
Set expectations early. In a meta-analysis of NB-UVB, 74% of patients achieved at least 25% repigmentation by 6 months, but only 19% reached 75% or more; the share with a marked response rose to 36% at 12 months. Response is usually fastest on the face and slowest on the hands and feet, whichever wavelength you choose.
Psoriasis: the 10% line
In psoriasis, the 2019 AAD–NPF phototherapy guidelines draw the line at roughly 10% body surface area. They recommend NB-UVB for generalised plaque psoriasis in adults, for guttate psoriasis at any age, and in pregnancy, and the excimer laser for localised plaque psoriasis under 10% BSA, for individual lesions within more extensive disease, and for scalp psoriasis. Both carry a grade A recommendation.
Clinical picture | First choice | Why |
Generalised plaque psoriasis (over ~10% BSA) | NB-UVB (311 nm) | Grade A; practical for large areas |
Guttate psoriasis | NB-UVB (311 nm) | Many small, scattered lesions; recommended at all ages |
Psoriasis in pregnancy | NB-UVB (311 nm) | Recommended option when systemic drugs are best avoided |
Localised plaques under ~10% BSA | Targeted 308 nm | Treats plaques without exposing clear skin |
Scalp psoriasis | Targeted 308 nm | Excimer laser reaches through hair to the plaque |
Palms and soles | Targeted 308 nm | Thick, resistant skin; fewer treatments at a lower cumulative dose than non-targeted phototherapy |
Mostly clear, but a few stubborn plaques remain | Targeted 308 nm on the remaining plaques | A focused finish after NB-UVB or systemic therapy |
Not all 308 nm sources perform the same. The guidelines rank the excimer laser above the excimer lamp, and both above localised NB-UVB for localised plaque psoriasis. For Indian patients specifically, a meta-analysis of NB-UVB in skin types III–IV found that 70.5% of patients reached PASI 75.
Eczema and atopic dermatitis: 311 nm, and second line
For eczema, the evidence supports narrowband UVB, not targeted 308 nm. The 2023 AAD guideline conditionally recommends phototherapy for adults with atopic dermatitis, on low-certainty evidence, and NB-UVB was the most studied option (13 clinical trials). A Cochrane review found NB-UVB may improve severity and itch, but could not draw firm conclusions for other light treatments.
Adults with widespread or persistent disease not controlled by topicals: NB-UVB (311 nm) is the option to consider.
Children: India's IADVL guidelines advise using NB-UVB only as second-line therapy because of possible long-term effects, under close supervision.
Targeted 308 nm: there is no guideline recommendation for eczema. Reserve it for individual cases where you have a clear clinical reason, and say so to the patient.
When the wrong wavelength is chosen
A mismatch rarely harms patients outright, but it costs them time, UV dose and motivation.
Targeted 308 nm on widespread disease means long sessions chasing dozens of lesions, missed subclinical areas, and new patches appearing between visits.
NB-UVB for a few localised plaques exposes large areas of clear skin to UV it doesn't need, adds to cumulative dose over the years, and can increase the contrast between tanned skin and vitiligo patches.
Either wavelength on the wrong expectations leads to drop-out. Patients who expected results in weeks often stop at month two, just before vitiligo repigmentation becomes visible.
308 nm sold as interchangeable sets up disappointment when a device with a thinner evidence base doesn't match published excimer results.
What getting it right looks like
When the wavelength matches the disease, treatment becomes simpler for everyone.
The patient gets the lowest UV dose that will work, a schedule they can keep, and realistic milestones to aim for.
Widespread disease is controlled with one consistent NB-UVB routine, and stubborn spots get a targeted boost instead of more whole-body exposure.
Localised disease is treated in fewer sessions, with clear skin left alone.
You spend follow-ups reviewing progress and adjusting doses, not restarting patients who gave up.
How UVThera supports both choices
UVThera is built in India to let you prescribe either wavelength and keep oversight once treatment moves home.
Both wavelengths, one system. 311 nm wands and lamps for larger areas, and 308 nm devices for targeted treatment, in home and clinic formats. Each device page states its light source, so you know what you are prescribing.
Your protocol, enforced. Set the starting dose and escalation schedule from the clinician dashboard; the patient's device follows it.
Oversight between visits. See session logs and adherence for every patient, and get notified when someone misses sessions or reports a reaction.
A dermatologist from day one. Every UVThera device includes a first consultation with a registered dermatologist, so no patient starts home phototherapy unassessed.
Next step: request clinician access on the UVThera Dashboard page at uvthera.com. It takes 30 seconds, and our team will call you to set up your dashboard.