Start with the comparison.
Open Glowhite’s side-by-side comparison on the screen you want to test. The two marks use different color encodings. On a compatible HDR rendering path, the HDR mark can appear brighter than ordinary white.
If they look the same, that is a useful observation—not proof that the file is broken. The available brightness range or the way the image is rendered may be limiting the effect.
What the label can tell you.
Glowhite checks the browser’s dynamic-range and color-gamut signals. These describe reported capabilities, not a measurement of the image on your display. In particular, the dynamic-range query does not establish that HDR is currently active.
The “HDR profile checked” message answers a different question: Glowhite found the expected color information in its generated file. It cannot verify what another browser, app or platform will do with that file.
Check the whole path.
Change one thing at a time so you can see where the difference comes from.
- Check the display’s HDR setting and any operating-system HDR controls.
- Keep the browser window on the screen you are testing.
- Compare another current browser on that same screen.
- Check whether a power-saving mode changes the result.
- Test the original download and the published copy separately.
Plan for ordinary screens.
Some renderers compress the highlights into a smaller brightness range; others may show a darker or otherwise different image. Do not assume a perfect fallback. If your artwork loses legibility, adjust it or use your original SDR version.