308nm UVB vs. 311nm Narrowband UVB: What’s the Difference?
Both wavelengths are used in medical UVB phototherapy. The practical choice depends less on a two-number contest and more on treatment area, device format, irradiance, prescribed dose and the condition being treated.
Published: Thursday, July 30 2026
10-minute read
311 nm narrowband UVB panels are built for broad coverage. Wellue 308 is built for the patches that need precision. Neither wavelength is automatically better. 308nm UVB combines targeted 308 nm LED phototherapy, 20 mW/cm² irradiance, a 20.25 cm² full treatment window, three interchangeable shield covers, dose-based J/cm² settings, and Wellue Guide for step-by-step guidance and area-by-area records.
The result is one focused home phototherapy system that can start broad, narrow down as a treatment area changes, and help you stay on plan without turning every session into guesswork.
The wavelength matters, but it does not tell you the size of the treatment field, the source technology, the output or the prescribed dose. Those details determine what the device is actually suited to do.
Decision factor
308nm UVB
311nm narrowband UVB
What the number describes
A single nominal wavelength within UVB.
A narrowband UVB source commonly described by its peak around 311nm; fluorescent lamps may peak between 310nm and 311nm.
Possible light sources
Excimer laser, excimer lamp or LED. “308nm” does not mean “laser.”
Fluorescent lamp, filtered source or other narrowband source; available in cabinets, panels.
Typical treatment geometry
Designed to target defined patches of affected skin.
Separate or adjoining patches can be treated as distinct areas, with an individual dose, skin-response and session history maintained for each patch in the Wellue 308 Guide.
A broad panel may expose several areas simultaneously, but it provides less patch-by-patch control over surrounding skin exposure.
Treatment time
The choice depends on diagnosis, extent, body site, skin response, device labeling, access, schedule, and the prescribing clinician’s plan. For localized patches, Wellue’s 20 mW/cm² treatment-surface irradiance is 5× that of the specified 4 mW/cm² lamp-based reference device, allowing the same prescribed UVB dose to be delivered in approximately one-fifth of the exposure time under comparable conditions.
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02 / Wavelength
What 308nm and 311nm actually mean
Nanometers describe wavelength. Both 308nm and 311nm sit within the UVB region, so the three-nanometer difference is real, but the label does not describe the entire treatment system.
A 308nm device can use an excimer laser, an excimer lamp or a light-emitting diode. Those sources may differ in beam shape, irradiance, treatment-window size, calibration and controls. Likewise, “311nm narrowband UVB” is often associated with fluorescent cabinets and panels, yet professional guidelines also recognize handheld and localized narrowband UVB devices.
308nm UVB is commonly delivered as targeted phototherapy for smaller, localized areas, while 311nm narrowband UVB is often delivered through a cabinet or panel when broader coverage is needed. Neither wavelength is automatically better. For Wellue, the advantage is a focused 308nm LED window with a current 20 mW/cm² specification, which can deliver the same prescribed UVB dose in less exposure time than a lower-irradiance device.
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03 / Treatment geometry
The biggest practical difference is often the area being treated
When psoriasis, vitiligo or eczema appears as a single patch, several adjoining patches or multiple patches scattered across different body areas, exposing a large surface of unaffected skin may be unnecessary. The Wellue 308nm targeted LED directs UVB through a 20.25 cm² full treatment window, with shield covers for smaller or more defined areas. This allows each physician-selected patch or section to be positioned separately while helping limit unnecessary exposure to surrounding skin.
A 311nm narrowband UVB panel or cabinet remains practical when most of an entire back, leg or another large continuous skin surface needs treatment. But broader coverage is not automatically more versatile. For patch-based treatment, it may expose more unaffected skin and provide less control over where UVB is delivered. The more practical format depends on whether the treatment plan calls for patch-matched precision or broad simultaneous exposure.
A targeted 308nm format may fit when…
When psoriasis, vitiligo or eczema appears as a single patch, several adjoining One or more defined patches are being treated, whether isolated, adjoining or scattered across different body areas.
Keeping UVB focused on involved skin and limiting unnecessary surrounding exposure are priorities.
A compact handheld format is useful for areas that are difficult to position under a broad panel.
Each patch benefits from separate dose guidance, skin-response checks and session records in the Wellue 308 Guide.
A 311nm handheld lamp, panel or cabinet may fit when…
A conventional replaceable-lamp system including periodic bulb replacement and output checks, fits the intended maintenance routine.
Exposing a broad area at once is more practical than positioning separate treatment sections.
A panel or cabinet is more practical for most of an entire back, limb or another large continuous skin surface.
Clinic access, supervision and equipment format align with the treatment plan.
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04 / Dose and time
Why “both are used for three minutes” is the wrong comparison
Phototherapy is prescribed as an energy dose to a defined skin area. Exposure time is one part of delivering that dose; it is not a universal treatment setting.
Delivered dose = irradiance × exposure time
Energy per area = power per area × seconds
If two devices have different irradiance, three minutes on each device delivers different energy. A higher-irradiance device may need less time to deliver the same prescribed dose.
Accurate dosimetry and regular irradiance checks are central to safe phototherapy; professional guidance does not treat time alone as the dose.2
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05 / Evidence
What the Evidence Says About 308nm and 311nm UVB
308 vs. 311 paired comparison
Localized 308nm excimer light vs. targeted 311nm NB-UVB
A randomized, single-blind study treated 36 symmetrical vitiligo lesions for 48 sessions. Within that protocol, the 308nm excimer-light side reached 25% repigmentation sooner on average and showed greater repigmentation at the end of treatment than the targeted 311nm side.4
308nm LED is recognized as a targeted format for localized vitiligo patches
A 2025 clinical review written by U.S. dermatology authors affiliated with Howard University College of Medicine describes 308nm light-emitting diode treatment as one of the handheld or targeted phototherapy formats used for localized vitiligo patches. This provides independent U.S. clinical-context recognition of 308nm LED as a targeted phototherapy technology.
German phototherapy guidance recognizes UVB-LED as an emerging clinical light source
The 2026 German S1 guideline on UV therapy and photochemotherapy includes a dedicated section on light-emitting diode technology. It notes that UVA- and UVB-LED sources have been investigated across multiple indications and specifically cites a prospective study comparing 308nm LED with 308nm excimer laser for localized psoriasis.
NB-UVB remains a broad, established phototherapy category
The 2022 BAD/BPG guideline describes NB-UVB as an established modality across multiple skin conditions, recognizes both whole-body and localized delivery, and emphasizes MED or test-area assessment, accurate dose measurement, training and ongoing support for home use.
Wellue is designed for patch-based treatment rather than whole-area exposure. It may be a practical fit when the treatment area does not cover an entire back, a whole leg or another large body region, but appears as a single defined patch, several adjoining patches or multiple patches distributed across different parts of the body. Its handheld 308nm LED and targeted treatment window help direct UVB to each patch individually while limiting unnecessary exposure to surrounding skin. For multiple or connected patches, users can work through the treatment area section by section.
The Wellue 308 Guide organizes manual-based starting-dose guidance by body-area category and maintains a separate treatment and skin-response history for each patch, helping users follow and document their clinician-directed home phototherapy plan over time.
Precision that fits the patch
Targeted 20.25 cm² window
Concentrates exposure on a defined area instead of illuminating a broad skin surface. Interchangeable covers can reduce the opening for smaller treatment areas.
Targeted 20.25 cm² window
Can shorten the exposure time required to deliver the same prescribed energy dose compared with a lower-irradiance device.
Area-by-area routine support
The Wellue 308 Guide helps users follow device instructions and keep separate dose and skin-response records. It does not diagnose or prescribe.
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07 / Choosing
How to discuss the choice with your clinician
The right question is not simply “Which wavelength is stronger?” A useful decision starts with the treatment map and then checks the device.
Diagnosis and disease activity: Confirm what is being treated and whether phototherapy is appropriate now.
Extent: Estimate whether the involved areas are limited, scattered or widespread.
Body site: Ask how location may affect response, positioning and protection of surrounding skin.
Device format: Compare spot/window size, handheld access and the practicality of treating every prescribed area.
Output and dose: Check irradiance, calibration, prescribed starting dose and the method for adjusting the dose.
Schedule and follow-up: Agree on treatment frequency, skin-response checks and when the plan should be reviewed.
Photosensitivity: Review medications, topical products, medical history and prior reactions to UV.
Regulatory status: Verify the exact model, intended use, prescription requirement and current device labeling. The Wellue 308nm UVB device (model SQ308PPWFG) is listed under FDA 510(k) K242908 as a Class II prescription phototherapy device for the home treatment of psoriasis, vitiligo and atopic dermatitis (eczema) on intact skin under physician guidance. Verify the official FDA clearance →
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08 / Safety
Home UVB phototherapy still requires a controlled plan
UVB is therapeutic radiation, not ordinary visible light. FDA explains that medical phototherapy uses carefully monitored UV doses and that overexposure can cause short- and long-term harm.3 The American Academy of Dermatology likewise describes home light boxes and handheld units as prescribed treatments used with dermatologist involvement.5
Use only as directed
Use the Wellue device on intact skin and under physician guidance, consistent with the cleared indications and labeling.
Follow prescribed eye protection, shielding and positioning instructions.
Do not copy another person’s time, dose or escalation schedule.
Report unexpected, persistent or severe redness, pain, blistering or other reactions to the prescribing clinician.
Ask about medicines and topical products that may increase UV sensitivity.
Keep treatment-area and skin-response records so the clinician can review the actual routine.
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09 / Quick answers
Frequently asked questions
Can the FDA-cleared Wellue 308nm device be used at home?
Yes. The Wellue 308nm UVB device (model SQ308PPWFG) is included under FDA 510(k) K242908 as a Class II prescription phototherapy device intended for home treatment of psoriasis, vitiligo and atopic dermatitis (eczema) on intact skin under physician guidance. Its targeted handheld design can be positioned over a single patch, several connected patches or multiple affected areas in different locations.
Is every 308nm device an excimer laser?
No. The number 308nm describes the wavelength, not the source. A 308nm device may use an excimer laser, an excimer lamp or an LED. When reading evidence, check which source and device were actually studied.
Is 311nm narrowband UVB always a full-body panel?
No. Cabinets and panels are common because they cover broad areas, but handheld and targeted 311nm devices also exist. A fair comparison needs both wavelength and treatment geometry.
Does higher irradiance mean faster results?
Not necessarily. Higher irradiance can reduce the exposure time needed to deliver the same prescribed energy dose. It does not prove that fewer sessions will be needed or that an individual will respond sooner.
Which is better for vitiligo: 308nm or 311nm?
There is no universal winner. Targeted 308nm treatment may fit limited patches, while 311nm NB-UVB is commonly used when broader coverage is needed. Location, extent, disease activity, device output and protocol all affect the choice. One paired-lesion study favored 308nm excimer light over targeted 311nm for the localized vitiligo lesions studied, but that result should not be generalized to every device.
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10 / Sources
Authoritative references
U.S. Food and Drug Administration — 510(k) K242908, covering Wellue model SQ308PPWFG
The FDA-listed models include SQ308PPWFG, the model used for the Wellue 308nm UVB device. The document confirms its Class II prescription-device classification, cleared indications, intact-skin limitation and home use under physician guidance. Open the FDA ↗
Goulden V, Ling TC, et al. BAD/BPG guidelines for narrowband UVB phototherapy, 2022
Evidence-based guidance on NB-UVB wavelengths, whole-body and localized delivery, dosimetry, MED testing and home-phototherapy governance. Read the guideline ↗
U.S. Food and Drug Administration — Ultraviolet (UV) Radiation
Regulator overview of UV wavelengths, exposure risks, photosensitizing products and carefully monitored medical phototherapy. Read the FDA overview ↗
Poolsuwan P, Churee C, Pattamadilok B. 308nm excimer light vs. targeted 311nm NB-UVB, 2021
Randomized, single-blind paired-lesion comparison in vitiligo. Photodermatology, Photoimmunology & Photomedicine. DOI: 10.1111/phpp.12619. View the PubMed record ↗
American Academy of Dermatology — Psoriasis treatment: Phototherapy
Patient-facing explanation of narrowband UVB, targeted excimer treatment, home light boxes and handheld devices, contraindications and follow-up. Read the AAD resource ↗
Title
Bring targeted 308nm treatment into your home routine
Designed for a single patch, several connected patches or multiple affected areas across different parts of the body, the Wellue 308nm UVB device concentrates treatment where it is needed without unnecessarily exposing a much larger area of skin. Explore its 20 mW/cm² irradiance, site-specific dose guidance, treatment tracking and FDA-cleared home-use indications.
