Eight bands of sunlight, what each one does, and what a supplement can and cannot replicate.

What this ray does

UVC sits at the high-energy end of the ultraviolet spectrum, from 100 to 280 nm, with a DNA absorption peak near 260 nm IARC Monographs, NCBI NBK304366. In laboratory and industrial settings, that absorption profile is what makes UVC germicidal: at the right doses it inactivates microbial DNA. In sunlight at ground level, none of this matters. Stratospheric ozone absorbs essentially all the UVC the sun produces, so the sun-driven UVC dose on your skin is functionally zero IARC NBK304366; UKHSA UV radiation guidance, 2025. UVC is in this tool for completeness, and because the question of germicidal UV lamps tends to come up alongside any honest discussion of sunlight.

Evidence grade: Strong.

How deep it goes

Not applicable at ground level: stratospheric ozone removes essentially all sun-driven UVC before it reaches the skin, so depth into tissue is not meaningful for this band Finlayson et al. 2022; IARC NBK304366.

Can a supplement replicate this?

Not applicable: the biological effect at ground level is zero, so there is nothing to replicate.

Not applicable. No sunlight UVC effect at ground level.

What to watch for

From sunlight, nothing: UVC does not reach you. The UVC concern sits with industrial and germicidal lamp settings, where workplace eye and skin exposure rules apply. That is a separate conversation from sun exposure, and this tool covers sunlight only. For sun safety, the bands that matter are UVB and UVA on the next two cards.

What this ray does

UVB sits at 280 to 315 nm under the modern ISO and CIE boundary (older dermatology literature uses 320 nm; the biology is unchanged), and makes up roughly 3.5% of the ultraviolet that reaches the ground Marionnet et al., PMC4307236. In the skin, UVB triggers two distinct local effects: it converts 7-dehydrocholesterol in keratinocytes to vitamin D3, which then enters the circulation and acts systemically Holick 2007, New England Journal of Medicine, and it activates the POMC pathway in those same cells, which releases beta-endorphin into the skin Fell et al. 2014, Cell. Beta-endorphin appears to stay largely local: whole-body UVR does not measurably raise plasma beta-endorphin Wintzen et al., PubMed 11722750, so the familiar "sunshine high" is better understood as a skin-local signal than a systemic opioid rise. UVB also causes the kinds of DNA changes in skin cells (pyrimidine dimers and p53 alterations) that drive sunburn and underpin the well-established case for sun safety IARC Monographs NBK304366; Cancer Research UK.

Evidence grade: Strong for vitamin D synthesis and DNA pathways; strong mechanism with moderate behavioural evidence for beta-endorphin.

How deep it goes

UVB penetrates roughly 0.1 mm, reaching the stratum corneum and upper epidermis but not the dermis Finlayson et al. 2022. This is why every effect above is keratinocyte-mediated.

Can a supplement replicate this?

Partly. Oral vitamin D3 closes the vitamin D gap: NHS guidance is 10 micrograms daily, and SACN's 2016 reference nutrient intake puts that at 10 micrograms year-round for the general population aged 4 and over. The other UVB effects (skin-local beta-endorphin signalling, and the cutaneous immune and DNA-repair pathways UVB triggers in keratinocytes) stay in the skin and are not replicable by anything you swallow.

Partial. Vitamin D only.

What this ray does

UVA sits at 315 to 400 nm, makes up about 95% of the ultraviolet that reaches the ground from the midday sun IARC Monographs, NCBI NBK304366, is present year-round in the UK, and penetrates cloud and window glass more readily than UVB British Association of Dermatologists Sun Protection Fact Sheet; Cancer Research UK. In the skin, UVA does something UVB does not: it releases nitric oxide from preformed cutaneous nitrite and S-nitrosothiol stores by a route that does not require nitric oxide synthase, which in controlled human studies produces an acute drop in blood pressure Liu et al. 2014, Journal of Investigative Dermatology; Opländer et al. 2009, Circulation Research. Population-scale evidence points in the same direction but is observational, so the cardiovascular case for sunlight stands as strong on mechanism and moderate on clinical translation Weller 2016, Blood Purification. UVA also drives photoageing through reactive-oxygen-species damage to collagen and elastin, and contributes through indirect oxidative pathways to the cumulative skin injury that UVB makes more direct IARC Monographs NBK304366; Cancer Research UK.

Evidence grade: Strong for the cutaneous NO mechanism and for photoageing; moderate for clinical-translation cardiovascular endpoints.

How deep it goes

UVA penetrates roughly 0.3 to 1 mm, reaching from the epidermis into the upper and mid dermis (including the papillary dermis at around 200 to 300 micrometres), which is why both the cutaneous nitrite chemistry and the photoageing effects above sit in this band rather than UVB's Finlayson et al. 2022.

Can a supplement replicate this?

No: the cutaneous NO chemistry sits in the skin and cannot be reproduced by anything you swallow, though dietary nitrate from beetroot and leafy greens contributes to systemic NO through a separate salivary-microbial pathway that complements rather than replicates the UVA route.

No. Dietary nitrate complements rather than substitutes.

What this ray does

The violet and blue visible band sits at 380 to 500 nm, with a real physical overlap with long-UVA between 380 and 400 nm. The key biology in this band is eye-mediated: in the retina, intrinsically photosensitive retinal ganglion cells (ipRGCs) carry the pigment melanopsin, which is maximally sensitive to blue light around 479 nm in humans Bailes and Lucas 2013, Proceedings of the Royal Society B; Berson, Dunn and Takao 2002, Science. These cells project to the suprachiasmatic nucleus through the retinohypothalamic tract and entrain the body clock to the daily light-dark cycle LeGates et al. 2014, Nature Reviews Neuroscience. Morning bright light through this pathway supports cortisol rhythm, alertness, and mood; evening blue-rich light through the same pathway suppresses melatonin and pushes sleep later, which is why the same biology cuts both ways depending on timing LeGates 2014.

Evidence grade: Strong for circadian entrainment mechanism; moderate for direct mood-and-alertness effects in humans beyond entrainment.

How deep it goes

Visible violet and blue penetrate roughly 0.5 mm into the epidermis and upper dermis Finlayson et al. 2022, though the relevant route for the biology above is not the skin but the eye, through retinal ipRGCs.

Can a supplement replicate this?

No: circadian entrainment and the alerting and mood effects above all require light reaching the eye, which nothing taken orally can substitute for.

No. The eye-light pathway has no oral equivalent.

What to watch for

This is not a sunburn band, so the considerations are timing and dose rather than UV protection. Evening blue-rich light from screens or bright indoor lighting suppresses melatonin and delays sleep onset LeGates et al. 2014; morning daylight to the eyes within roughly an hour of waking anchors the same biology in the helpful direction LeGates 2014. Not through glass, and not behind sunglasses for that morning window.

What this ray does

The green and yellow visible band sits at 500 to 590 nm, with peak human photopic visual sensitivity around 555 nm (vision-science textbook standard). Biologically, this is largely a visual-function band: cones in the retina translate it into the colours you see, and no major systemic non-visual pathway runs through it at this level of resolution. The one specific finding that has held up in primary literature is narrow: 520 ± 10 nm green light reduces migraine photophobia in people with migraine Noseda et al. 2016, Brain, with follow-up real-world headache-diary data supporting the same narrow effect Frontiers in Neurology 2023, PMC10582938. That finding does not extrapolate beyond the narrow wavelength range and the specific clinical context: the wider "green light is healing" framing some popular sources use is not supported by the primary literature.

Evidence grade: Strong for the general visual-function biology; moderate and narrow for the 520 ± 10 nm migraine photophobia finding.

How deep it goes

Green and yellow visible penetrate roughly 1 to 2 mm, reaching upper to mid dermis Finlayson et al. 2022, but as with the violet and blue band the relevant route for the visual and narrow-band migraine biology is the eye rather than the skin.

Can a supplement replicate this?

No: visual function and the narrow-band migraine photophobia modulation both happen through the eye and brain pathways and cannot be reproduced by anything taken orally.

No. The visual pathway has no oral equivalent.

What to watch for

This is not a sunburn band, and ordinary daylight exposure carries no significant safety concern in this range. If you live with migraine and find green-tinged environments easier on the eyes during an attack, the Noseda 2016 work explains the mechanism, not a self-management protocol: migraine care is a conversation to have with your GP or neurologist.

What this ray does

Red visible sits at 620 to 700 nm. The 590 to 620 nm orange interval that comes just before is biologically quiet at this level of resolution, matching the photobiomodulation literature that clusters effective wavelengths at red and longer Karu 1999, Journal of Photochemistry and Photobiology B; Hamblin 2017, AIMS Biophysics. The primary chromophore for red-light biology is cytochrome c oxidase, the mitochondrial respiratory complex IV, with absorption peaks near 620, 660 and 670 nm; activation at these wavelengths is associated with increased mitochondrial ATP output and a set of secondary signals including transient ROS, calcium handling, and anti-inflammatory transcription-factor modulation Karu 2008, Photochemistry and Photobiology; Hamblin 2018, Photochemistry and Photobiology. Most of the clinical literature here comes from device-delivered photobiomodulation rather than sunlight specifically, so the mechanism stands as strong while the clinical translation to outdoor sunlight is moderate Hamblin 2017.

Evidence grade: Strong for the cytochrome c oxidase mechanism; moderate for clinical endpoints, with most data from device-delivered photobiomodulation rather than sunlight directly.

How deep it goes

Red visible penetrates roughly 2 to 5 mm, reaching from the mid dermis into subcutaneous tissue Finlayson et al. 2022, which is the depth range where red-light biology engages mitochondria in living dermal and subcutaneous cells.

Can a supplement replicate this?

No: photobiomodulation requires actual light delivered to tissue because the mechanism depends on photon absorption by mitochondrial chromophores, so no oral supplement reproduces it.

No. Photon delivery to tissue is the route.

What to watch for

This is not a sunburn band, and ordinary daylight exposure in this range carries no significant safety concern. The interesting story for red light sits in the biology above, not the safety side.

What this ray does

Near infrared sits at 700 to 1400 nm and shares its primary chromophore with red light: cytochrome c oxidase, with notable absorption peaks at 810 and 830 nm where most NIR photobiomodulation studies sit Hamblin 2018, Photochemistry and Photobiology; Karu 1999, Journal of Photochemistry and Photobiology B. The same mitochondrial activation pattern described for red light applies here, with the difference being depth: NIR reaches further into tissue than red, into superficial muscle and joint structures. NIR is associated with modest pain reduction in some musculoskeletal studies, with more recent transcranial NIR work on cognitive and mood applications that sits at emerging rather than established Hamblin 2018. As with red light, most of the human evidence comes from device-delivered photobiomodulation rather than sunlight specifically, so the mechanism stands as strong while the clinical translation to outdoor sunlight is moderate Hamblin 2017, AIMS Biophysics.

Evidence grade: Strong for the cytochrome c oxidase mechanism (shared with red light); moderate for clinical endpoints in musculoskeletal applications; emerging for transcranial cognitive and mood applications.

How deep it goes

Near infrared penetrates roughly 5 to 10 mm, reaching subcutaneous tissue and superficial muscle Finlayson et al. 2022; water absorption rises sharply above 950 nm, which means the deepest reach sits at the band's shorter wavelengths where the cytochrome c oxidase peaks (810, 830 nm) also concentrate.

Can a supplement replicate this?

No: as with red light, photobiomodulation at near-infrared wavelengths requires actual light delivered to tissue because the mechanism depends on photon absorption by mitochondrial chromophores, with no oral substitute.

No. Photon delivery to tissue is the route.

What to watch for

This is not a sunburn band, and ordinary daylight exposure in this range carries no significant safety concern. As with red light, the interesting story for NIR sits in the biology above rather than the safety side.

What this ray does

Mid and far infrared spans roughly 1400 nm to about 1 mm. Unlike the near-infrared band on the previous card, the mechanism here is thermal, not photochemical: water in the skin absorbs these wavelengths strongly, the surface warms, and heat then conducts into deeper tissue (optical and heat-transfer physics). The warming triggers secondary responses including thermal-receptor signalling and vasodilation; regular sauna use is associated with modest improvements in cardiovascular indices in clinical studies Shui et al. 2015, Experimental Biology and Medicine; Tsagkaris et al. 2025, Frontiers in Cardiovascular Medicine. Most of that clinical evidence comes from sauna research rather than direct sunlight, and far-infrared evidence is thinner than near-infrared evidence in the broader photobiomodulation literature, so the picture for this band stands as moderate with an honest sauna-versus-sunlight caveat Shui 2015.

Evidence grade: Strong for the thermal mechanism (water absorption, vasodilation); moderate for cardiovascular improvements in clinical studies, with the data coming mostly from sauna research rather than direct sunlight.

How deep it goes

Unlike the photochemical bands above, mid and far infrared do not have a single penetration depth: water in the superficial dermis absorbs the wavelengths at the surface, and the heat then conducts into deeper tissue through the body's normal thermoregulatory pathways Shui et al. 2015.

Can a supplement replicate this?

No: supplements cannot create warmth or trigger thermoregulatory vasodilation; the body's heat response requires actual heat input.

No. Supplements cannot create warmth.