Modern glow powder is strontium aluminate activated with rare-earth dopants — not the old zinc sulphide. It charges from light and releases that energy slowly as visible afterglow, far brighter and longer than legacy materials.
| SrAl₂O₄ (modern) | ZnS (legacy) | |
|---|---|---|
| Afterglow brightness | High | Low |
| Afterglow duration | Hours | Minutes |
| Stability | Good (with care) | Degrades faster |
Afterglow is "free" energy borrowed from a charge source — sunlight, a lamp or UV. Green and yellow-green are the brightest and longest; blue and purple exist but fade sooner. Finer grades disperse better in coatings; coarser grades glow more intensely per particle but can feel gritty.
Q: Does glow powder work without any light ever hitting it?A: No. It is phosphorescent, not a battery — it must be "charged" by light first. In permanent darkness it eventually goes dark.
Q: Can I mix it into a clear epoxy for signs?A: Yes, and that is a common use. Avoid excessive heat during cure and keep it well dispersed; a clear topcoat protects the cured part.