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Advanced: duty cycle
Flashing-light warning
Visual pulsing at 3 Hz or higher can trigger seizures in photosensitive users, including some with epilepsy or migraine.
lightswitch.me caps the brightness change (±12%) and your screen is not a therapeutic light source — this is only a timing indicator. You can always turn off visual pulsing in Profile → accessibility.
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Education hub
Evidence-led, plain-language primer on light therapy. Citations at the bottom. This is not medical advice.
Wavelengths — which colours do what
| Range | Label | Penetration | Primary effect | Best-studied use |
|---|---|---|---|---|
| 10,000 lux broadband | Bright white | Retina → suprachiasmatic nucleus | Melatonin suppression, alerting, circadian anchoring | Seasonal affective disorder |
| 495–570 nm | Green | Retina (not transdermal at therapy doses) | Central analgesic pathway — not via cytochrome-c oxidase | Fibromyalgia, migraine |
| 600–700 nm (esp. 660 nm) | Red | ~1–3 mm into skin | Photoactivates cytochrome-c oxidase → ATP, NO, mild ROS | Skin, superficial joints, microcirculation |
| 780–900 nm (esp. 810/830/850) | Near-infrared | ~2–3 cm tissue; ~1% reaches cortex | Same mechanism as red — deeper reach, including brain | Chronic pain, transcranial |
| Dim warm red (evening) | Circadian-friendly | Retina | Low melanopic response; allows melatonin rebound | Evening wind-down |
How it works inside a cell Strong evidence
Red and near-infrared light is not heat — it's a key that fits a specific molecular lock inside your mitochondria.
- Chromophore: cytochrome-c oxidase (Complex IV of the mitochondrial electron transport chain) absorbs red/NIR via its heme and copper centres .
- First-order effect: photon absorption displaces inhibitory nitric oxide from the binding site → electron transport resumes → ATP synthesis rises, with a brief reactive-oxygen-species burst and NO release.
- Downstream: altered calcium signalling, activation of transcription factors (NF-κB, AP-1), modulation of inflammation, and cell proliferation / migration.
- Biphasic dose response (Arndt–Schulz): low-to-moderate doses stimulate; high doses inhibit. More minutes under a panel is not always better.
- Secondary chromophores: recent work implicates light-gated ion channels and skin opsins in some effects — the mechanism story is broader than CCO alone .
Pulsing — what the Hz actually do
Flickering the light at specific rates is hypothesised to entrain brain rhythms. Evidence quality varies sharply by band.
7 Hz · ThetaPreliminary
Theta is the EEG band of drowsy relaxation and light meditation. Direct PBM studies entraining human theta are sparse; most evidence is correlational (meditators show more theta) rather than causal. A reasonable default for wind-down protocols.
10 Hz · AlphaModerate
10 Hz visual flicker reliably produces steady-state visual evoked potentials ~3× larger than 30 Hz, enhances alpha spectral power, and reduces flanker interference on attention tasks . A 2023 feasibility trial used pre-sleep 10 Hz alpha stimulation in chronic widespread pain: nightly pain dropped by 0.53 on a 0–10 scale, sleep quality rose 0.39 on 0–5 . Individual alpha peak frequency (typically 8–13 Hz) moderates the effect — a fixed 10 Hz is sub-optimal for some.
40 Hz · GammaEmerging, contested
MIT's Tsai lab showed 40 Hz flicker reduces amyloid-β load in transgenic mouse models of Alzheimer's via microglial activation; 20 Hz and 80 Hz didn't replicate the effect — frequency specificity is a real finding . Human pilots show safety and modest cognitive signals. Replication is incomplete: independent labs have struggled to reproduce the amyloid result under similar conditions, so treat the Alzheimer's claim as unresolved rather than established.
Duty cycle
The percentage of each cycle the light is on. 50% is the common default. Higher duty delivers more total photons but a weaker rhythmic signal. The Advanced control in a session sets this 10–90%.
Photosensitive-epilepsy safety. Flashes at 3 Hz or above are a seizure risk; the most provocative band is 15–25 Hz . WCAG 2.0's "three flashes per second" rule derives from this guidance. lightswitch.me caps visual pulsing at ±12% brightness and gates strobing ≥3 Hz behind an acknowledgement prompt. If in doubt, turn on Disable visual pulsing in Profile.
Evidence by condition
Each card: a plain-language summary, the recommended protocol, the best study, and what we still don't know. Tap to expand.
Photobiomodulation vs Optogenetics
| PBM (this app) | Optogenetics (research) | |
|---|---|---|
| How it works | Red / near-infrared light shone on intact skin or scalp | Light activates genetically-engineered light-sensitive proteins inside specific neurons |
| Consumer-available | Yes — panels, pads, helmets | No — research labs only |
| Invasiveness | Non-invasive, no genetic modification | Requires genetic modification and typically implanted fibers |
| Safety profile | Generally low-risk when used as directed; eye protection advised | Surgical / experimental risks; not for humans outside regulated studies |
| Typical use | Wellness support: pain, sleep, mood, recovery | Mapping and probing neural circuits in animal models |
| Evidence base | Growing, mixed — strongest for SAD, some pain and recovery | Nobel-recognized research tool (not a treatment) |
Mentioned here for awareness only. lightswitch.me will never ask you to do anything involving genetic modification.
Safety & contraindications
- Eye safety. Never stare at a therapy source. Bright-light side effects (eye strain, headache, nausea) are typically mild and resolve within a week.
- Photosensitive epilepsy / migraine with aura. Avoid visual pulsing ≥ 3 Hz; most provocative band 15–25 Hz .
- Photosensitizing medications. Doxycycline and other tetracyclines, retinoids (isotretinoin, tretinoin), amiodarone, chlorpromazine, methotrexate, voriconazole, St John's Wort, 5-ALA / porphyrins. Ask a pharmacist if uncertain.
- Directly over vulnerable tissue. Avoid illuminating active cancers (until cleared by oncology), active haemorrhage, the pregnant abdomen, or the thyroid without clinician guidance.
- Start short. 5 minutes, tolerate, then build toward protocol duration.
- Bottom line. If symptoms worsen or anything feels wrong, stop and consult a clinician.
Glossary
- PBM / LLLT
- Photobiomodulation (also known as low-level light/laser therapy). Use of non-heating doses of red or near-infrared light to stimulate cells.
- Cytochrome-c oxidase (CCO)
- Complex IV of the mitochondrial electron transport chain; the primary chromophore for red/NIR light in PBM.
- NIR
- Near-infrared light, roughly 700–1100 nm. Penetrates tissue more deeply than visible red.
- SSVEP
- Steady-state visual evoked potential — a rhythmic EEG response to a flickering stimulus at the same frequency.
- Lux
- A measure of illumination on a surface. 10,000 lux is the standard therapeutic intensity for bright-light boxes.
- mEDI
- Melanopic equivalent daylight illuminance — light intensity weighted for its effect on the melanopsin-containing retinal cells that drive circadian timing.
- Entrainment
- Synchronisation of an internal oscillation (a brain rhythm, the circadian clock) to an external rhythmic driver.
- Biphasic dose response
- A pattern where low-to-moderate stimulation helps and high doses hinder — named the Arndt–Schulz law in pharmacology.
- Duty cycle
- The fraction of a repeating pulse cycle that the light is on, expressed as a percentage.
References
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