Light Therapy — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

Light therapy (phototherapy) is the therapeutic application of controlled wavelengths and intensities of visible, ultraviolet, or near-infrared light to treat a range of medical conditions through well-established photobiological mechanisms. It encompasses several distinct clinical modalities. Bright light therapy (BLT) uses high-intensity broad-spectrum white light (10,000 lux at 30–60 cm) to suppress melatonin secretion and shift circadian rhythms, used in seasonal affective disorder (SAD), non-seasonal depression, sleep phase disorders, and shift-work disorder. Narrowband ultraviolet B (NB-UVB, 311–313 nm) phototherapy is the primary outpatient treatment for widespread or recalcitrant plaque psoriasis, atopic eczema, vitiligo, polymorphous light eruption, and other photoresponsive dermatoses; it exploits UVB's immunomodulatory effects on T lymphocytes in the skin. Psoralen plus UVA (PUVA) photochemotherapy combines a photosensitising psoralen drug (8-methoxypsoralen or 5-methoxypsoralen) with UVA irradiation (320–400 nm) to treat psoriasis, mycosis fungoides, lichen planus, and vitiligo unresponsive to NB-UVB. Blue light phototherapy (420–470 nm) is the standard treatment for neonatal hyperbilirubinemia (jaundice), degrading unconjugated bilirubin in the skin. Low-level laser therapy (LLLT) and photobiomodulation (PBM) using red and near-infrared light (630–1000 nm) at low non-thermal fluences stimulate cellular energy production (ATP synthesis) and are used for musculoskeletal pain, wound healing, and hair loss (low-level laser for androgenetic alopecia).

The appropriate candidate depends entirely on the specific light therapy modality and indication. Bright light therapy is recommended for patients with seasonal affective disorder (SAD) — a recurrent major depressive episode with a seasonal pattern — and is endorsed by NICE and the American Psychiatric Association as first-line treatment alongside antidepressants or psychotherapy. It is also used for non-seasonal depression, bipolar depression (with caution), sleep-wake rhythm disorders, and jet lag. Narrowband UVB phototherapy is indicated for moderate-to-severe plaque psoriasis (body surface area above 10%, or disease affecting functionally important areas), atopic dermatitis inadequately controlled by topical steroids and calcineurin inhibitors, active spreading vitiligo, and mycosis fungoides (patch and plaque stage cutaneous T-cell lymphoma). PUVA is reserved for patients who fail NB-UVB, due to its higher carcinogenic risk with cumulative UVA exposure. Blue light phototherapy is indicated for neonatal jaundice with total serum bilirubin above exchange transfusion threshold as defined by gestation-specific nomograms (American Academy of Pediatrics). Photobiomodulation is used in musculoskeletal pain clinics, wound care, and hair loss clinics with moderate evidence for pain relief and wound healing.

Bright light therapy: the patient sits 30–60 cm from a 10,000 lux bright light lamp for 20–30 minutes each morning, ideally within the first 30 minutes of waking. The eyes should be open but not looking directly at the lamp. The light unit should be commercially certified for therapeutic BLT use, as regular household lamps are insufficient. Treatment begins in autumn when symptoms emerge and continues until spring. Narrowband UVB phototherapy: performed in a hospital dermatology phototherapy unit in a floor-standing or booth-type fluorescent tube cabinet emitting NB-UVB (311 nm). Treatment frequency is typically 3 times per week (Monday-Wednesday-Friday) to allow skin recovery. Starting doses are determined by the patient's minimal erythema dose (MED) or skin phototype. Dose is escalated by 10–20% each session, targeting a barely perceptible erythema. Genital and facial skin is shielded unless being treated. A typical course requires 24–36 sessions over 8–12 weeks. For PUVA, the patient takes an oral psoralen (8-MOP 0.6 mg/kg) 2 hours before UVA irradiation, or bathes in dilute psoralen solution for 15 minutes immediately before irradiation. Eyes must be protected with UVA-blocking wrap-around sunglasses for 24 hours after oral psoralen ingestion. Neonatal blue light phototherapy: the newborn is placed naked in a phototherapy unit, eyes protected with UV-blocking pads. Maximum skin surface area is exposed. Serum bilirubin is monitored every 4–12 hours. Treatment continues until bilirubin falls to a safe level.

Bright light therapy achieves remission of seasonal affective disorder in 50–80% of patients, comparable to antidepressant medication, with effects typically apparent within 1–2 weeks — faster than the 4–6 week response time of most antidepressants. A landmark meta-analysis by Golden et al. (JAMA 2005) confirmed that bright light therapy was significantly superior to placebo for both SAD and non-seasonal depression, with an effect size comparable to antidepressant pharmacotherapy. It carries no systemic drug side effects, is low-cost after the initial lamp purchase, and can be used during pregnancy when antidepressants require careful consideration. Narrowband UVB phototherapy achieves PASI 75 (75% improvement in Psoriasis Area and Severity Index) in 65–75% of patients with plaque psoriasis after a standard course of 24–36 sessions, with complete clearance (PASI 90–100) in 30–40% — clinically meaningful improvements in quality of life, itch, and sleep. NB-UVB is safe in pregnancy and paediatric patients (psoriasis, vitiligo), avoiding systemic immunosuppression. Vitiligo repigmentation occurs in 50–70% of patients with facial lesions after 12 months of NB-UVB, with less complete responses on acral sites. Blue light phototherapy for neonatal jaundice reduces the need for exchange transfusion — a much higher-risk procedure — in virtually all mild-to-moderate cases of neonatal hyperbilirubinaemia, and is effective within 12–24 hours.

Bright light therapy is very safe; reported side effects include mild headache, eyestrain, irritability, and insomnia if used in the late afternoon rather than morning. In patients with bipolar disorder, bright light therapy can precipitate hypomania or mania and must be used under psychiatric supervision with mood monitoring. Narrowband UVB phototherapy: the principal risk is cumulative ultraviolet exposure. NB-UVB is genotoxic and carcinogenic; however, the carcinogenic risk of NB-UVB at therapeutic doses is substantially lower than PUVA or outdoor UV exposure and requires very high cumulative doses (above 200–300 sessions) before the risk of non-melanoma skin cancer becomes clinically significant. Acute over-exposure causes sunburn-like erythema, blistering, and pain, avoided by careful dose escalation. NB-UVB may precipitate photo-aggravated conditions including systemic lupus erythematosus and should be avoided in these patients. PUVA: higher cumulative carcinogenicity than NB-UVB (squamous cell carcinoma risk increases after 200 PUVA sessions), requires lifetime oncological skin surveillance. Oral PUVA may cause nausea from psoralen (mitigated by taking with food). PUVA is contraindicated in pregnancy, children under 12, and severe renal or hepatic impairment. Blue light phototherapy: bronze baby syndrome (skin bronzing) may occur in neonates with conjugated hyperbilirubinaemia — serum direct bilirubin should be checked before initiation. Retinal phototoxicity requires eye shielding. Hyperthermia from the phototherapy unit requires temperature monitoring.

Bright light therapy requires no recovery period. Sessions are typically performed at home each morning, taking 20–30 minutes. Patients can read, eat, or use a computer during the session while positioned near the lamp. Treatment is continued throughout autumn and winter for SAD patients and stopped in spring when natural daylight increases. Dermatological phototherapy: following each NB-UVB session, the treated skin may be mildly pink for 2–4 hours — this erythema guides dose escalation. No sun exposure or sunbed use is permitted on treatment days to avoid additive UV exposure. Sunscreen SPF 30+ is applied to all non-treated sun-exposed skin daily throughout and after the course. Following a full NB-UVB course, 50–70% of psoriasis patients remain clear for 3–6 months; maintenance phototherapy (once weekly) extends remission duration in some units. Annual full skin examination is recommended for patients who have received more than 100 NB-UVB sessions or any PUVA therapy. Neonatal blue light phototherapy: serum bilirubin is checked every 4–12 hours during treatment and phototherapy discontinued when bilirubin falls below the treatment threshold. A rebound bilirubin check 6–24 hours after stopping phototherapy confirms that bilirubin is not rebounding before discharge.