Phototherapy & Ultraviolet Light: Core Concepts and Clinical Applications

I. Fundamentals

1. What is Light?

Dual nature: Electromagnetic wave + particle (photon) stream

Wave properties: Wavelength, frequency, reflection, refraction

Particle properties: Discrete energy quanta, photoelectric effect, radiation pressure

Generation mechanism: Atoms/molecules in excited state → ground state → release excess energy as photons + electromagnetic waves → luminescence

Example devices: red light therapy light (low-level laser/LED, 630–680 nm) for non-thermal bio-stimulation

red light therapy for skin

2. What is Phototherapy?

Physical therapy using light's radiant energy for treatment or cosmetic purposes

Includes: infrared phototherapy, visible light, ultraviolet (UV), red light therapy light, photochemotherapy (e.g., PUVA)

Goal: Maximize beneficial effects (sterilization, tissue repair, anti-inflammatory modulation) while minimizing adverse reactions

II. Ultraviolet Rays: The Core "Tool" of PhototherapyClassification of UV Radiation (Figure 1-1)

Band	Wavelength	Atmospheric Penetration	Clinical Relevance
UVC (Short-wave)	180–280 nm	Blocked by ozone → negligible surface exposure	Rarely used (germicidal lamps only)
UVB (Mid-wave)	280–320 nm	<10% of sunlight	Core band for psoriasis & vitiligo
UVA (Long-wave)	320–400 nm	~90% of sunlight	Used in PUVA (with psoralen); infrared phototherapy often combined for deeper tissue effects

"Double-Edged Sword" Effects of UV on Skin

Beneficial Effects	Adverse Effects
→ Vitamin D synthesis	→ Erythema (sunburn)
→ Improved blood circulation & wound healing	→ Hyperpigmentation
→ Bactericidal action	→ Photoaging
→ Pain relief	→ Phototoxic reactions
→ ↑ Melanin production	→ Skin cancer risk (esp. PUVA)
→ Keratinocyte control (psoriasis)

Note: Red light therapy for skin (630–660 nm) complements UV by reducing inflammation and accelerating healing without DNA damage risk.

define sterilization in microbiology

III. UV Light Sources in Phototherapy

Classification by Spectrum & Bandwidth

Type	Spectrum	Key Features
BB-UVB	Wide (280–320 nm)	Older, less selective
NB-UVB	311 ± 3 nm	>85% energy at 311 nm; safer
UVA1	340–400 nm (peak 365 nm)	For scleroderma, eczema

Classification by Technology (Figures 1-2 & 1-3)

Source	Description	Status
Fluorescent lamps	Most widely used UV source	Standard
LED arrays	Portable, stable, precise	Emerging - also powers full body red light therapy panels
Excimer (308 nm)	Targeted, high-intensity	Focal lesions

IV. Key Clinical Phototherapy Bands1. Narrow-Band UVB (NB-UVB) – Gold Standard

1.Peak: 311 ± 3 nm

Energy: >85% at 311 nm; <0.1% <290 nm

Indications: Psoriasis, vitiligo, atopic dermatitis

Devices: Full-cabin, handheld (Figure 1-4)

"311" = NB-UVB shorthand

2. 308 nm Excimer – Targeted Precision

Source: Excimer lamp/laser

Peak: 308 nm

Best for: Localized vitiligo, palmoplantar psoriasis

Advantage: Spares healthy skin

"308" = Targeted UVB

Summary Table: Phototherapy Modalities

Modality	Wavelength	Device Type	Best For	Safety
NB-UVB	311 ± 3 nm	Cabin / Handheld	Widespread psoriasis, vitiligo	Low erythema
308 nm Excimer	308 nm	Targeted	Focal lesions	High local dose
PUVA	UVA + Psoralen	Full-body	Severe psoriasis	↑ Cancer risk
Full body red light therapy	630–680 nm	LED panel	Pain, inflammation, red light therapy for skin rejuvenation	Non-ionizing, safe

Key Takeaway:
NB-UVB (311 nm) remains first-line for psoriasis/vitiligo. Full body red light therapy and infrared phototherapy expand the spectrum into non-UV, non-ionizing modalities for inflammation, pain, and cosmetic red light therapy for skin applications.

Figures referenced:

Fig 1-1: UV spectrum

Fig 1-2: Fluorescent UVB cabin

Fig 1-3: LED red light therapy light panel prototype

Fig 1-4: NB-UVB treatment schematic