UV light, skin and invisible exposure: sources & model

Build a virtual light filter, uncover a missing patch, explore real skin microscopy and inspect a DNA structure. Discover why visible light and warmth cannot tell the whole story.

What supports the explanation?

What this model assumes

1. Source lines and filter transmissions are authored; no product or sunlight is calibrated.
2. Colored markers are explanatory, not counted photons, fluorescence or the appearance of UV.
3. There is no skin penetration, scattering, heating, reaction-rate, mutation or clinical-risk solver.
4. The equal-area grid assumes uniform normal illumination. A real product needs its own measurements.
5. Erythema weighting describes one reference endpoint. Outside its domain does not mean harmless.
6. The measured spectrum remains an image; no fabricated samples or absolute-power equivalence is supplied.
7. Microscopy shows stained normal tissue, not an exposure experiment. No spatial calibration is invented.
8. Molecular coordinates are preserved; comparison is not a reaction trajectory.
9. Name the bands: Using the WHO convention, UVA spans 315–400 nm, UVB 280–315 nm and UVC 100–280 nm. These are naming boundaries, not biological cliffs. Some sources use a 320 nm UVA boundary. Our 305 and 365 nm examples are unambiguous under either convention. We do not model an unattenuated UVC beam as ordinary ground-level sunlight.
10. One watt per square meter, four times: The authored source supplies 1 W/m² in each of four monochromatic channels: 305, 365, 550 and 1000 nm. Each value is channel-integrated irradiance, not W/m²/nm. Their sum is 4 W/m². This artificial four-line source is not a solar or screen spectrum. Irradiance is arriving power per area; it is not temperature or a visible-brightness score.
11. Same power per area, different photons: For one photon, E = hc/λ. NIST’s defining constants give about 4.0651 eV at 305 nm and 3.3968 eV at 365 nm. At 1 W/m², arrival rates are about 1.5354 × 10¹⁸ and 1.8375 × 10¹⁸ photons per second per square meter. Equal irradiance does not mean equal photon counts per second per area. Both travel at the same speed in vacuum. Photon energy alone does not determine a biological outcome.
12. The coverage equation: For cover transmission T and uncovered fraction g, the mean outgoing fraction is g + (1 − g)T under uniform illumination. With T = 0.10 and g = 0.20, the mean is 0.28. Uncovered regions supply 0.20/0.28 ≈ 71.43% of the transmitted channel. Moving the same gaps changes the local map but leaves this area average unchanged.
13. Optical bookkeeping: Each covered cell transmits T and absorbs 1 − T; uncovered cells transmit everything. Reflection, scattering, fluorescence and angle dependence are omitted. Absorbed plus transmitted irradiance equals the incident value per channel. Absorption can contribute to heating, but the bench has no heat capacity, cooling law or temperature calculation.
14. A weighting needs a named purpose: The optional technical table uses the erythema-reference weighting printed in NOAA’s NEUBrew report. Its weight is about 0.219786 at 305 nm and 0.000407380 at 365 nm: a ratio of about 539.51. This endpoint-specific convention is not an absorption spectrum, universal DNA-damage factor or individual forecast. Our four-line weighted sum is not a measured outdoor UV Index.
15. The molecular surprise: A cis-syn cyclobutane pyrimidine dimer can connect neighboring thymine units on the same DNA strand. In 1TTD, the highlighted extra links are C5–C5T and C6–C6T inside component TTD. Normal opposite-strand pairing is different. Whole-skin experiments reported these lesions after UVA as well as UVB exposure; “UVA only ages, UVB alone damages DNA” is misleading.
16. What the structure actually is: McAteer and colleagues used solution NMR constraints and structural calculations. We render one deposited conformer each from 1TTD and parent duplex 1COC, preserving their coordinates. Each has 761 modeled atoms, 486 excluding hydrogen. The damaged structure has 23 residue records because one TTD record represents two linked thymine units; the parent has 24. This is not a deleted nucleotide. Switching structures compares them; it does not replay a reaction.
17. Damage, mutation and disease differ: A chemical lesion, a lasting sequence mutation and cancer are not interchangeable. Cells have repair and other responses; not every lesion becomes a mutation. A structure establishes geometry, not a repair rate or a clinical probability. This lesson collects no skin photos and predicts no individual safe exposure time.
18. A microscope image has a purpose: The Human Protein Atlas section is normal thin skin stained with hematoxylin and eosin. Staining reveals features. It does not represent natural skin color, UV penetration or damage after exposure. No spatial calibration is supplied for this derivative, so we do not invent a micrometer scale or reconstruct a measured 3D tissue volume.
19. A peak is not a whole spectrum: Lawrence and colleagues measured finite-width spectra for experimental 385 and 405 nm sources. Figure 7 is normalized: a peak of 1 does not establish equal absolute irradiance. Reported widths are 7 and 10 nm. The 405 nm source includes shorter wavelengths. Their high-dose experimental setup is not evidence that an ordinary phone produces the same exposure.
20. SPF is not a stopwatch: FDA describes SPF in terms of relative sunburn-producing energy, not a guaranteed multiplier for time in the sun. A single SPF number is not a transmission spectrum. Broad-spectrum labeling and actual instructions matter. Our imaginary cover assigns no product SPF. Use the linked WHO and FDA guidance for real-world protection.

What has been checked

Analytical reference cases, conservation or transition invariants, finite drawing commands, bounded setup parsing, discovery and route integrity are checked automatically. These checks do not establish anatomical fidelity, learner outcomes or browser/device compatibility. Independent subject review, learner trials, comprehensive accessibility review and browser video encoding checks remain pending.

Each source supports the associated claim. Sources do not certify this implementation or its visuals.

About the cover illustration

Actual render of Brytalearn’s original four-channel optical bench. False-color UVB detector; authored source and cover settings, not a measured product or tissue exposure.