Protection and timing
Check hourly UVI, specific measures and teaching-example conditions.
Read protection actions and citationsEvidence and sources
Read an action and trace its basis
Find sources for protection, daylight use, routines and seasonal food choices. Locate an action in a guide, then check population, conditions and whether its basis is institutional advice, research or a product rule. The 30° product prompt is confirmed, with evidence scope on its rule page.
Find sources for the action you want to check
Daylight use and purpose
Distinguish daytime light, skin UVB and actual exposure conditions.
Read the complete guide and citationsSeasons and the 30° rule
Check place, date, calculation examples and prompt purpose.
Read the confirmed rule and evidence scopeFoods and portions
Check source country, food processing, labels and units.
Read food data and citationsDistinguish the concepts first
From spectra and body clocks to daily protection
The spectrum helps explain what sunlight contains
Visible and invisible lightUV, visible light, and infrared are different bands. A spectrum describes light by wavelength. Brightness, warmth, and UV levels need separate consideration.
The 2017 Nobel Prize and circadian rhythms
Body clocks and environmental lightThe award-winning work revealed molecular mechanisms controlling circadian rhythms. Environmental light received by the eyes helps the body clock stay in sync with day and night. This mechanism alone cannot determine personal exposure duration or sleep outcomes.
UV Index (UVI)
A reference for UV protectionDescribes UV levels weighted for skin erythema to help explain protection needs. It does not represent all UV energy, heat risk, or an individual vitamin D dose.
WHO recommends beginning protective measures
UVI ≥ 3Actual outdoor exposure also depends on location, time, weather, and surroundings. Check local UV information.
The UV band involved in vitamin D synthesis in skin
UVBSeason, time, clouds, skin colour, and actual exposure affect UV reaching the skin. UVI or solar angle cannot establish individual nutritional status.
The 晒研社 seasonal food-source prompt condition
Below 30°When local daily maximum solar elevation is below 30°, the rule prompts attention to food sources of vitamin D. It is a product rule, not a skin-synthesis cut-off or an indication of deficiency.
How to read sources
Beyond the citation, consider the research question
Consider the type of material
Institutional guidance, research papers, and astronomical calculations have different purposes. A mechanism or research association does not prove a product's effects.
Consider the scope
The people studied, setting, and conditions affect whether conclusions apply to everyday understanding. Articles aim to explain the scope actually checked.
Distinguish product rules
30° is the 晒研社 seasonal rule for prompting attention to food sources of vitamin D. It is not a medical threshold or an assessment of individual nutritional status.
Continue exploring
Our articles and common questions
Sunlight guide (21 articles)
Visible light: sunlight, colour, and the sky we see · 2026-10-15
UV basics: how do UVA, UVB, and UVC differ? · 2026-10-15
Use shadows to understand the sun's position · 2026-10-15
How do glass, shade, and clouds affect sunlight? · 2026-10-15
Sunlight, UV, and vitamin D: 6 common misconceptions · 2026-10-15
Understanding the UV Index before going outdoors · 2026-10-15
Daytime light, evening lighting, and daily routines · 2026-10-15
Where can you get vitamin D from food? · 2026-10-25
What should you do first for red or sunburnt skin? · 2026-10-15
Planning time outdoors in autumn · 2026-10-16
FAQ (12 answers)
Read short answers about UV protection, outdoor activities, food sources of vitamin D, and sun protection for infants and young children, or visit the FAQ page.
Source links lead to public materials. Research questions and populations may differ between sources. Read the explanations in the article alongside the references.
Content preparation and corrections
Content is compiled by 晒研社 with AI assistance in drafting and editing. The website is operated by 亲壳科技（北京）有限公司. Cited institutions and original authors are not reviewers of this website, and citations do not imply their endorsement of the website or its products.
This content has not received a final review by medical experts. Read it alongside the original sources and stated limits of applicability; do not use it as a basis for personal medical decisions.
Article dates indicate the latest content update; dates on frequently asked questions indicate when sources were checked. These are not research publication dates or medical review dates. Errors and broken sources can be reported by email; relevant content and records will be revised after verification.
A practical path to checking a claim
Find the claim in the article, then open its nearby citation or listed source. Check the title, organisation, date, population and setting. If only an abstract is available, use what it reports rather than assume the full text has been verified.
For UV protection, begin with WHO information; for vitamin D sources, NIH information; for a solar-position product prompt, first read our rule. This page gathers entry points so you can trace a claim and continue reading in context.