Light Environment and Health: The Strong Evidence Is Free, the Money Flows to the Weak End

Summary

Light is a genuine health input with a lopsided evidence map that runs opposite to the market: the interventions with Strong evidence — bright days, dark nights, morning light timing, outdoor daylight for children — all cost nothing, while the products sold on light fear or light promise (blue-blocker glasses, "circadian" bulbs, infrared panels, $1,000 masks) cluster at the weak end of the map — from Moderate-with-sponsorship down to Experimental and unsupported — so the honest doctrine is a split: what your light does by TIMING and PATTERN matters and is increasingly disease-relevant, while c

Why Strong

Tier: the hub carries a HIGH-confidence organising thesis, with per-spoke tiers spanning Foundational to Experimental. The load-bearing claims — the four-region tier map, the cost inversion, and the split firewall — each rest on the strongest evidence in their region: a formal consensus for timing, a cluster RCT plus replications for childhood day intensity, a large objective-sensor prospective arc (ceiling-labelled) for light at night, and formal-body nulls for spectrum.

NOT a lower tier for the headline, because the ordering is not speculative — it is what the evidence hierarchy shows, and the uncertainty lives inside individual spokes (especially the one-cohort ceiling on light-at-night), not in the ordering itself.

NOT Foundational as a blanket label, because the hub deliberately routes to regions at Moderate, Emerging, and Experimental; averaging the spread away is exactly the error both sales camps profit from.

The per-sub-area tier split (read this, not just the headline):
• Circadian timing (bright days / dim, dark nights; morning light): Strong/Foundational — consensus plus decades of experimental circadian work; the specific numeric thresholds are consensus-derived, not outcome-trial-derived.
• Bright light therapy, seasonal and non-seasonal depression: Strong.
• Day intensity, children (myopia prevention): Strong; dose band and national-programme corroboration: Moderate.
• Day intensity, adults (mood, mortality direction): Moderate.
• Light at night, hard outcomes: Moderate ceiling (one cohort, one consortium); experimental causal bridge: Emerging; rodent mechanism: animal-only.
• Spectral quality of consumer light as a health variable: unsupported; the null (no retinal risk, blue-blocker futility) is Strong.
• Flicker: Foundational as regulation; Strong as measurement (the retina registers flicker well above the visibility threshold); Moderate as symptom evidence; screen-PWM symptoms Emerging, prevalence unquantified.
• Consumer red/NIR devices: per-indication, Strong-with-COI (hair) down to Experimental (glucose, infrared-deficiency hypothesis).

Practical takeaway

This is a hub. The section below is the family tier map: it routes, it does not re-argue. Hold the tier, go to the spoke.

TIMING — Strong/Foundational, free. Do these first.
• Morning light exposure. Anchors circadian phase; the best-supported daily light habit. Go to morning_sunlight_exposure.
• Bright days, dim evenings. The consensus targets and how to hit them indoors. Go to circadian_rhythm_optimization.
• Dark bedroom, lights genuinely off. Owns sleep-darkness practice; now reinforced by the metabolic evidence. Go to darkness_and_sleep.
• Bright light therapy. Strong for seasonal depression and now meta-analytically supported for non-seasonal depression as an adjunct. Go to light_therapy_seasonal_and_beyond.
• Shift work. The occupational ceiling of circadian disruption and what mitigates it. Go to shift_work_circadian_health.

DAY INTENSITY — Moderate in adults; Strong in children via myopia.
• Outdoor time for children. Randomised-trial-grade myopia prevention, about two hours daily at outdoor light levels; shade counts, windows largely don't. The strongest light-health receipt in existence. Go to outdoor_light_and_childhood_myopia.
• Daylight and vitamin D / sensible sun. The UV half of the outdoor-time ledger. Go to light_exposure_vitamin_d.
• The full daylight-versus-indoor comparison. The one-stop treatment of what daylight provides that bulbs don't. Go to artificial_light_vs_sunlight.

LIGHT AT NIGHT — Moderate-emerging; the fix is free.
• Light at night and metabolic disease. The dose-response story from bedroom lamp to night shift — diabetes, mortality, mood — with the one-cohort ceiling stated. The action is a dark bedroom, under about 3 lux. Go to light_at_night_and_metabolic_health.

SPECTRUM QUALITY — Experimental or unsupported. Spend nothing here.
• Blue-blocker glasses. Probably useless for eyestrain, indeterminate for sleep; dim-warm evenings are the evidenced alternative and cost nothing. Go to blue_light_blocking_evening.
• Screens and eyes. Blink-rate and dryness, not retinal damage. Go to dry_eye_and_screen_eye_strain.
• Flicker. The one spectrum-adjacent exposure with real standing — regulated by EU law, with modest double-blind symptom evidence concentrated in headache-prone people. Screen-PWM exposure is verified physics, but its symptom prevalence is unquantified — the circulating prevalence figures are vendor marketing. Go to light_flicker_and_temporal_light_modulation.
• Red-light and infrared devices. Per-indication tiers from the category's one strong claim (hair) down to Experimental; the dose arithmetic that shows daylight out-delivers most consumer devices for free; the infrared-deficiency hypothesis firewalled. Go to red_light_therapy_devices_evidence_and_dose, with mitochondrial_health for the mechanism spine.

The framing to hold: fix timing first, then day intensity, then darkness at night — all free — and treat every spectral product claim as unproven until its spoke says otherwise. The order is by evidence, not by price, and in this category price runs backwards.

Evidence detail

Why This Entry Exists

The light family in this knowledge base now spans more than a dozen entries — circadian timing, morning light, darkness, blue blockers, seasonal and non-seasonal light therapy, shift work, screens and eyes, vitamin D, and four newer entries covering light at night and metabolic disease, childhood myopia, flicker, and red-light devices. Each spoke carries its own evidence in depth. This hub exists to hold the map: which claims are strong, which are emerging, which are unsupported, and where each question should be routed. It does not re-argue any spoke.

It also exists because light is a market with two opposing sales forces and one inconvenient fact. The wellness industry sells fear of "junk light" — blue-blocker lenses, bulb replacements, screen filters — and sells its mirror image, light as a product: red-light masks, infrared panels, tunable "human-centric" luminaires. The lighting industry amplifies a legitimate academic consensus on daytime light levels to move premium fixtures. The inconvenient fact both share an interest in burying is the cost inversion, which is this hub's first canonical statement: every light intervention with Strong, independent evidence is free (time outdoors, morning light, a genuinely dark bedroom, bright days), while the priced end of the market runs from Moderate down to Experimental — with a single exception, hair-loss devices, the category's one Strong claim carrying a price tag, and its evidence base is manufacturer-sponsored. Money in this category flows toward the weakest-evidenced tiers.

The second canonical statement is the split firewall, because "does artificial light cause disease?" has two different answers depending on which clause you mean. Spectral claims stay firewalled: there is no good evidence that the spectrum of ordinary consumer light — screens, LED bulbs — damages retinas or drives disease, and the formal safety bodies plus a Cochrane review of blue-blocking lenses back that. The pattern clause has moved: whether your days are bright and your nights are dark is now associated with hard outcomes — type 2 diabetes, mortality, depression — in dose-responsive, objectively-measured epidemiology, with a small experimental causal bridge. That evidence has a stated ceiling (one cohort, one consortium) and is labelled Moderate at its strongest, but it is no longer a wellness overclaim.

What bad advice this protects against, in all directions:
• "Blue light from your screen is damaging your retina — you need blocker glasses." Wrong at consumer intensities. The French and EU safety agencies and the American Academy of Ophthalmology find no consumer-level retinal risk from screens and lamps, and the Cochrane review of blue-blocking lenses found they probably do nothing for eyestrain, with sleep effects indeterminate. The real screen issues are circadian timing and blink-rate, both owned by other spokes.
• "Light hygiene is wellness fluff — light can't affect disease." Also wrong, and it now cedes real ground: outdoor time prevents myopia in children at randomised-trial strength, bright light treats non-seasonal depression at meta-analytic strength, and light-at-night now carries dose-responsive associations with diabetes and mortality on objective sensors. The dismissive position was defensible five years ago; it is not the honest reading today.
• "Modern life has an infrared deficiency — buy this NIR panel/mask." The infrared-deficiency idea is a self-labelled hypothesis stacking several unproven links, and its lead author sells near-infrared lighting. Meanwhile the free source exists: ordinary daylight from mid-morning to mid-afternoon delivers red and near-infrared at intensities inside the therapeutic window the device literature itself uses.
• "Watch the sunrise to get your red-light dose." Golden hour is red-rich in proportion but photon-poor in dose — in-band irradiance at sunrise is roughly forty to ninety times lower than midday, by standard atmospheric physics calculation. Sunrise keeps its genuine credits (circadian phase-setting and near-zero UV); a photobiomodulation dose is not one of them.
• "Upgrade to full-spectrum or circadian bulbs for your health." Full-spectrum lighting's health claims failed critical review a quarter-century ago, colour-rendering metrics are appearance metrics with no health content, and the lighting-engineering profession's own body has stated human-centric lighting "is not a product feature." No lighting product has outcome-trial support.

This entry owns the family tier map, the cost-inversion statement, the split firewall, and the routing. It defers every exposure's and every device's evidence detail to its spoke and does not re-litigate it here.

Evidence

Read the tiers, not the thesis. Each claim below is an anchor for one region of the map; the spoke named beside it carries the depth.

Circadian timing — the settled centre (Strong, as formal consensus).

1. Expert consensus recommends bright days (at least 250 melanopic lux at eye level in daytime) and dim evenings (10 or less in the pre-sleep hours), and typical indoor environments miss the daytime target badly. This is a formal consensus statement derived from laboratory endpoints — melatonin suppression, phase shifting, alertness — not an outcome trial of the thresholds themselves; typical offices at around 500 photopic lux still fall well short of the daytime melanopic target, and homes are worse. CONSENSUS, not outcome-trial evidence. (Brown TM et al., PLOS Biology 2022;20:e3001571. Cui bono: the lighting industry cites this consensus to sell tunable luminaires the consensus never tested; the consensus itself is independent academic work and endorses no product.) Detail: circadian_rhythm_optimization, morning_sunlight_exposure.

2. Bright light therapy works for non-seasonal depression, not just seasonal. Meta-analysis of 11 randomised controlled trials (n=858): remission 41% versus 23% with mostly adjunctive morning bright light; blinding in light trials is imperfect by nature. HUMAN RCT meta-analysis. (Menegaz de Almeida A et al., JAMA Psychiatry 2024, doi:10.1001/jamapsychiatry.2024.2871. Cui bono: light boxes are cheap commodity hardware; no meaningful industry push, which strengthens the signal.) Detail: light_therapy_seasonal_and_beyond.

Day intensity — Strong in children, Moderate in adults.

3. Adding outdoor time prevents childhood myopia at randomised-trial strength. A cluster randomised trial of ~1,900 children adding 40 minutes of daily outdoor school time cut three-year myopia incidence from 39.5% to 30.4%; replications with objective light meters support a protective band at or above roughly 1,000–2,000 lux sustained, and Taiwan's national outdoor-time programme coincided with reversal of a decades-long decline in children's vision. HUMAN cluster RCT plus objective-sensor cohorts plus a national natural experiment. (He M et al., JAMA 2015;314(11):1142; Wu PC et al., Ophthalmology 2018;125:1239 and 2020;127:1462. Cui bono: nothing is sold — as conflict-free as evidence gets. The commercial pressure in this space sits with violet-light eyewear and red-light-laser device vendors, both firewalled in the spoke.) Detail: outdoor_light_and_childhood_myopia.

Light at night — the clause that moved (Moderate ceiling, stated per-claim).

4. Objectively-measured night light predicts hard outcomes dose-dependently — with a one-cohort ceiling. In ~85,000–89,000 UK Biobank participants wearing wrist light sensors for a week: incident type 2 diabetes rose dose-dependently with night light (hazard ratios 1.29/1.39/1.53 across exposure groups, independent of polygenic risk), all-cause mortality was 21–34% higher in the brightest-night decile while brighter days were protective, and night light associated with roughly 30% higher depression odds while day light ran the other way. HUMAN observational, prospective for diabetes and mortality. The entire disease arc is one cohort analysed by one consortium, one week of light data stands in for years, and reverse causation is live — the ill are awake and lit at night. Ceiling: Moderate, watching for independent replication. (Windred DP et al., Lancet Reg Health Eur 2024;42:100943, PMID 39070751; Windred DP et al., PNAS 2024;121:e2405924121; Burns AC et al., Nature Mental Health 2023;1:853. Cui bono: darkness is free — nobody profits from this finding, which is a point for its credibility.) Detail: light_at_night_and_metabolic_health.

5. The experimental causal bridge exists but is small. One night at 100 lux raised next-morning insulin resistance in a controlled lab study (n=20), through a sympathetic pathway with melatonin unchanged — the effect ran through closed eyelids. HUMAN experimental, small, Emerging. (Mason IC et al., PNAS 2022;119:e2113290119, PMID 35286195. Independent academic.) Detail: light_at_night_and_metabolic_health, darkness_and_sleep.

Spectrum quality — the firewalled end (claims fail; the null evidence is Strong).

6. No consumer-level retinal risk from screens or lamps, and blue-blocking lenses probably do nothing for eyestrain. Formal risk assessments (ANSES 2019, SCHEER 2018, American Academy of Ophthalmology guidance) find no retinal-damage risk at consumer intensities and identify circadian disruption as the real concern; the Cochrane review of blue-blocking lenses (17 RCTs) found probably no effect on eyestrain and indeterminate effects on sleep. FORMAL-BODY consensus plus systematic review — Strong, in the negative direction. (ANSES 2019; SCHEER 2018; Singh S et al., Cochrane 2023 CD013244, PMID 37593770. Cui bono: the blue-blocker market depends on the opposite claim; the safety agencies sell nothing.) Detail: blue_light_blocking_evening, artificial_light_vs_sunlight, dry_eye_and_screen_eye_strain.

7. Lighting-product health claims have no outcome-trial support. Full-spectrum lighting's health claims failed critical review; workplace-lighting intervention trials are very low quality as a body; "circadian lighting" as a product category has no outcome trials, and the profession's own body says human-centric lighting is not a product feature. NEGATIVE findings and absence-of-evidence, stated as absence. (McColl SL & Veitch JA, Psychol Med 2001, PMID 11513381; Pachito DV et al., Cochrane 2018 CD012243. Cui bono: the tunable-luminaire market runs directly against these findings.) Detail: artificial_light_vs_sunlight.

The device carve-out — intensity, not spectrum ideology, is the hazard variable.

8. Engineered high-irradiance devices genuinely can injure retinas; screens cannot. Repeated low-level red-light myopia devices have a published retinal-injury case report, independent measurements showing some devices exceed laser safety classification limits, and a regulatory reclassification to the strictest device class in China. CASE REPORT plus PHYSICS MEASUREMENT plus regulatory action. (Liu H et al., JAMA Ophthalmology 2023; Ostrin LA & Schill AW, Ophthalmic Physiol Opt 2024;44:241. Cui bono: device vendors' sponsorship has outpaced independent safety validation.) Detail: outdoor_light_and_childhood_myopia, red_light_therapy_devices_evidence_and_dose.

The free golden ticket — daylight physics (Foundational as physics; the health inference stays with the spokes).

9. Midday-to-mid-afternoon daylight delivers roughly 20–35 mW/cm² in the 600–900nm red/near-infrared band — inside the 25–50 mW/cm² window the photobiomodulation literature itself prefers — full-body and free; sunrise and sunset deliver roughly 0.5–3 mW/cm² in-band, forty to ninety times less. PHYSICS: the midday figures are band integrals over the standard solar reference spectrum (scout arithmetic, ±15%); the low-solar-elevation figures are CALCULATED from standard atmospheric physics, not measured spectral datasets. Golden hour is red-rich in proportion, photon-poor in dose: its real credits are circadian phase and near-zero UV. The free ticket is not cost-free — peak free near-infrared and peak UV arrive on the same beam. (ASTM G173 / AM1.5G reference spectrum. Cui bono: neither industry states this — device vendors because daylight is free competition, sun-maximalist influencers because the UV coupling complicates the pitch.) Detail: red_light_therapy_devices_evidence_and_dose, artificial_light_vs_sunlight, light_exposure_vitamin_d.

Mechanism

Light reaches health through three distinct channels, and keeping them separate is most of the doctrine.

The timing channel (non-visual photoreception). Intrinsically photosensitive retinal ganglion cells expressing melanopsin feed the circadian clock, melatonin control, and alertness — this is the channel behind morning-light timing, evening dimness, light therapy, and shift-work disruption. It responds to intensity and timing far more than to fine spectral quality, which is why timing advice is robust and spectral products are not. There is also rodent evidence for a clock-independent retina-to-mood circuit — a mechanism for light acting on mood beyond melatonin — held at Emerging and labelled ANIMAL.

The pattern channel (autonomic and metabolic). Light at night appears to act at least partly through sympathetic activation rather than melatonin: in the one controlled human experiment, insulin resistance moved while melatonin did not, through closed eyelids. This is why "I fall asleep fine with the TV on" does not answer the metabolic question. Rodent work (Fonken 2010, PNAS — 5-lux dim light at night, weight gain via mistimed feeding) adds a mechanism — ANIMAL, never to be presented as human evidence.

The intensity/dose channel (ocular and photochemical). Sustained outdoor-level illuminance in childhood protects against myopia — the leading mechanistic candidate, retinal dopamine, is ANIMAL evidence. At the other extreme, engineered high-irradiance devices can exceed photochemical safety margins; ordinary screens and bulbs are orders of magnitude below them. Red/near-infrared photobiomodulation claims run through mitochondrial chromophores — that mechanistic story and its limits live in mitochondrial_health and red_light_therapy_devices_evidence_and_dose, not here.

Risks And Contraindications

• Do not let the pattern evidence be sold back as spectrum products. The disease-risk evidence concerns bright-versus-dark timing, measured in lux — not colour temperature, not "junk light," not anything a special bulb fixes. The evidenced response is free.
• The free ticket carries UV. Midday daylight delivers therapeutic-window red/near-infrared and peak UV on the same beam; sun-exposure judgement defers to light_exposure_vitamin_d and the skin-safety entries. Never convert the daylight-dose arithmetic into "more midday sun is always better."
• Engineered high-irradiance devices are the real ocular hazard. Repeated low-level red-light devices have a published injury case and measurements exceeding laser safety limits; never generalise "light devices are harmless" across the intensity spectrum. Detail in the myopia and red-light spokes.
• Bright light therapy has clinical contraindications (notably bipolar disorder, where morning bright light can precipitate mixed or manic states without clinical oversight) — defer to light_therapy_seasonal_and_beyond.
• Do not moralise darkness at shift workers. Their light pattern is occupational, not a hygiene failure; mitigation belongs to shift_work_circadian_health.
• Children's outdoor time trades against UV exposure — the myopia spoke and the sun-safety entries carry the balance; the hub holds only that both ledgers are real.

Controversy

Nature: the controversy is not whether light affects health — timing evidence settled that — but which claims graduate from wellness narrative to evidence, and both commercial camps have an answer that serves them.

Position A — the light-maximalist / product camp (wellness vendors, parts of the lighting industry). Best evidence: the Biobank light-pattern arc is real, dose-responsive, and objectively measured; the daytime consensus targets are genuine academic work; indoor environments really are melanopically poor. Where it overreaches: it converts a timing-and-intensity evidence base into spectrum products the evidence never tested — tunable luminaires riding a consensus statement that endorses no product, blue-blockers riding a Cochrane null, infrared panels riding a hypothesis whose lead author sells the product, and masks riding trial protocols run on different hardware.

Position B — the dismissive camp ("light hygiene is wellness fluff"). Best evidence: the spectral fear claims really did fail — no consumer retinal risk, blue-blockers null, full-spectrum claims failed review, and plenty of light-wellness marketing is unverifiable. Where it overreaches: it is now behind the data. Childhood outdoor time is randomised-trial-grade prevention, bright light is a meta-analytically supported depression adjunct, and light-at-night disease risk is objectively-measured, dose-responsive epidemiology with an experimental bridge — dismissing the whole category means dismissing those too.

The funding/bias dimension — cui bono, both ways. The product camp's incentive is explicit: fear and promise both convert to hardware sales, and the key trials behind several device categories are manufacturer-sponsored. The dismissive camp's bias is subtler — blanket dismissal sounds rigorous while sparing its holder any behaviour change, and some of the loudest "blue light is fine" messaging is adjacent to industries (displays, evening media) that benefit from the conclusion. The academic consensus sits between the camps and endorses neither product class.

Realised Position: hold the split. Timing and pattern are real health variables — act on them, for free. Spectral quality of ordinary consumer light is not an evidenced disease variable — spend nothing on it. Label the light-at-night disease arc Moderate with its one-cohort ceiling named, keep the retinal and infrared-deficiency claims firewalled, and treat the cost inversion as the consumer's most useful single fact: in this category, evidence strength and price are inversely correlated.

Cross-Pillar Connections

Genuinely cross-pillar: light touches sleep, mental health, metabolic health, eyes, and skin, so this hub routes across all four pillars.
• artificial_light_vs_sunlight owns the one-stop daylight-versus-indoor comparison and the firewall's full statement; this hub holds only the split-firewall summary and routes there for depth.
• morning_sunlight_exposure owns morning-light timing practice; this hub holds only its Strong placement — and the caution that golden hour's credit is circadian, not a red-light dose.
• darkness_and_sleep owns bedroom-darkness practice; this hub holds only its placement, now reinforced by the metabolic arc.
• circadian_rhythm_optimization owns the consensus light targets and indoor melanopic poverty; this hub holds only the Strong-consensus label.
• blue_light_blocking_evening owns the blue-blocker evidence including the Cochrane null; this hub holds only the "spend nothing here" placement.
• light_therapy_seasonal_and_beyond owns bright light therapy, seasonal and non-seasonal; this hub holds only its Strong placement.
• shift_work_circadian_health owns occupational circadian disruption and mitigation; this hub holds only the routing.
• dry_eye_and_screen_eye_strain owns screen-related eye symptoms and their real mechanism; this hub holds only that the mechanism is blink-rate, not spectrum.
• light_exposure_vitamin_d owns the UV half of the outdoor ledger; this hub holds only that peak free near-infrared and peak UV share a beam.
• mitochondrial_health owns the chromophore mechanism spine behind photobiomodulation claims; this hub defers all mechanism depth there.
• light_at_night_and_metabolic_health owns the bedroom-lamp-to-night-shift dose-response story and its single-cohort caveat; this hub holds only the Moderate-emerging label.
• outdoor_light_and_childhood_myopia owns the strongest receipt in the family and the device safety carve-out; this hub holds only the Strong label and the intensity-is-the-hazard rule.
• light_flicker_and_temporal_light_modulation owns flicker regulation, symptom evidence, and screen-PWM honesty; this hub holds only its placement.
• red_light_therapy_devices_evidence_and_dose owns per-indication device tiers, the dose arithmetic, and the firewalled infrared-deficiency hypothesis; this hub holds only the cost-inversion frame.

What would change our mind

Industry bias note

Sources (18)

• Brown TM, Brainard GC, Cajochen C, et al. (2022). "Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults." PLOS Biology;20:e3001571. (Independent academic consensus; no product endorsed.) 250 melanopic lux daytime / 10 or less pre-sleep — consensus derived from laboratory endpoints, not an outcome trial.↗
• He M, Xiang F, Zeng Y, et al. (2015). "Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China." JAMA;314(11):1142–1148. (Independent academic; nothing sold.) Cluster RCT, ~1,900 children: +40 min/day outdoor time cut 3-year myopia incidence 39.5% → 30.4%.↗
• Wu PC, et al. (2018). Ophthalmology;125:1239 (pubmed.ncbi.nlm.nih.gov/29371008↗/" target="_blank" rel="noopener">PMID 29371008↗) and (2020) Ophthalmology;127:1462. (Independent academic.) Objective light metering supporting the ≥1000–2000 lux protective band; Taiwan's national outdoor-time programme and the reversal of the children's vision trend.
• Windred DP, et al. (2024). "Personal light exposure patterns and incidence of type 2 diabetes." Lancet Regional Health — Europe;42:100943 (pubmed.ncbi.nlm.nih.gov/39070751↗/" target="_blank" rel="noopener">PMID 39070751↗). (Independent academic; darkness is free.) 84,790 participants, objective wrist sensors: night light → incident T2D, HR 1.29/1.39/1.53, independent of polygenic risk. One cohort, one consortium.
• Windred DP, et al. (2024). "Brighter nights and darker days predict higher mortality risk." PNAS;121(43):e2405924121. (Independent academic.) 88,905 participants: brightest-night decile +21–34% all-cause mortality; brighter days protective.↗
• Burns AC, et al. (2023). Nature Mental Health;1:853. (Independent academic; cross-sectional.) Night light +30% depression odds; day light −20%; 86,772 participants.↗
• Mason IC, et al. (2022). "Light exposure during sleep impairs cardiometabolic function." PNAS;119:e2113290119 (pubmed.ncbi.nlm.nih.gov/35286195↗/" target="_blank" rel="noopener">PMID 35286195↗). (Independent academic.) One night at 100 lux raised next-morning insulin resistance (n=20); sympathetically mediated, melatonin unchanged.
• Fonken LK, et al. (2010). PNAS;107:18664. (Independent academic; RODENT.) 5-lux dim light at night → weight gain via mistimed feeding — mechanism only, never presented as human evidence.↗
• Menegaz de Almeida A, et al. (2024). "Bright Light Therapy for Nonseasonal Depressive Disorders." JAMA Psychiatry, doi:10.1001/jamapsychiatry.2024.2871.↗ (Independent academic meta-analysis; commodity hardware.) 11 RCTs, n=858: remission 41% vs 23%, mostly adjunctive morning light; blinding imperfect.
• ANSES (2019). Report AP2019SA0139; SCHEER (2018) opinion on LED health effects; American Academy of Ophthalmology guidance. (Government/formal safety bodies; sell nothing.) No consumer-level retinal risk from screens/lamps; circadian disruption named as the real concern.↗
• Singh S, et al. (2023). "Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults." Cochrane Database of Systematic Reviews CD013244 (pubmed.ncbi.nlm.nih.gov/37593770↗/" target="_blank" rel="noopener">PMID 37593770↗). (Independent systematic review; contradicts an entire product category.) 17 RCTs: probably no eyestrain benefit; sleep effects indeterminate; no macular RCT evidence at all.
• McColl SL, Veitch JA. (2001). "Full-spectrum fluorescent lighting: a review of its effects on physiology and health." Psychological Medicine (pubmed.ncbi.nlm.nih.gov/11513381↗/" target="_blank" rel="noopener">PMID 11513381↗). (Independent academic.) Full-spectrum lighting's health claims failed critical review.
• Pachito DV, et al. (2018). "Workplace lighting for improving alertness and mood in daytime workers." Cochrane Database of Systematic Reviews CD012243. (Independent systematic review.) Workplace-lighting intervention trials are very low quality — the intervention layer is thin.↗
• Liu H, et al. (2023). JAMA Ophthalmology — retinal injury case following repeated low-level red-light myopia therapy. (Independent case report; runs against device-vendor interests.) n=1, partial recovery.↗
• Ostrin LA, Schill AW. (2024). "Red light instruments for myopia exceed safety limits." Ophthalmic and Physiological Optics;44:241 (doi:10.1111/opo.13272↗). (Independent physics measurement.) Some devices exceed laser safety classification limits.
• Fernandez DC, et al. (2018). Cell;175:71. (Independent academic; MOUSE.) ipRGC → perihabenular mood circuit, clock-independent — mechanism only, never presented as human outcome evidence.↗
• ASTM G173 / AM1.5G solar reference spectrum. (Standards body; physics.) Basis for the midday ~20–35 mW/cm² in-band figure (band integral, ±15%); sunrise/sunset in-band figures (~0.5–3 mW/cm²) are calculated from standard atmospheric physics, not measured spectral datasets.↗
• Funding notation: the Strong tier's independently-funded claims — outdoor time, darkness, morning light, bright light therapy — come from academic and formal-body work with no product attached; the one Strong claim carrying a price (hair-loss devices) is manufacturer-sponsored, and the remaining product tiers (blue-blockers, circadian luminaires, red/NIR devices) rest on manufacturer-sponsored trials, unverifiable marketing figures, or hypotheses with direct commercial stakes. The entry weights accordingly, in both directions.*↗

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