How we grade
Two questions sit behind every page on this site. Does this kind of product do anything for your body clock? And if it does, which models do it best?
Sunlight first
Free light and darkness come before any purchase. Every category page opens with what daylight and a dark bedroom already do, with sources, and a product earns a place only when it fills a gap they cannot: waking before sunrise, winter at high latitudes, shift work, or a bedroom you cannot make dark. When a device claims to beat or replace sunlight, we check that claim against the research like any other.
Evidence grades
Each category and guide gets one letter. The letter rates the research on the product type, not any brand.
| Grade | What it means | What it takes |
|---|---|---|
| A | Strong | A meta-analysis or several randomized controlled trials in people, mostly agreeing |
| B | Moderate | Some randomized trials, but small, short, or not all pointing the same way |
| C | Limited or mixed | A few small or lab-based human studies, or results that conflict |
| D | Weak or none | No good human trials, or good trials showing little or no effect |
We read the studies, not the press releases. If a meta-analysis exists we start there. We link every source on the page so you can check our reading.
A grade can differ by use. Blue-light glasses are a good example. The evidence for eye strain is weak, while the evidence for wearing amber lenses in the evening to protect melatonin is better. When that happens we say so in the text.
How products get on the list
- The spec that does the job comes first. For a light therapy lamp that is lux at a stated distance. For a red light panel it is irradiance in mW/cm² at a stated distance, plus wavelengths. For blue-blocking lenses it is the transmission curve.
- We prefer independently measured numbers. Manufacturer figures are listed as manufacturer figures. Where an independent measurement disagrees, we say so.
- We do not invent test results. Listings are built from published specs, independent measurements and user-reported problems. Nobody on this site pretends to have used something they have not.
- Prices are approximate. They are list prices in USD on the date shown and change often.
- Rank is about fit. Each pick says who it suits. A cheaper product that does the core job well can outrank a premium one.
Money
Some links earn a commission. Commission rates are never part of the ranking, and a product with no affiliate program can rank first. See the affiliate disclosure.
Corrections
If a spec, price or study reading is wrong, email hello@circadian.supply. We fix errors and update the date on the page.