"Tritium" sights are self- contained. They "glow" in low-light-no-light on their own. They don't require any outside source to work, such as recharging from natural light. Tritium sights produce their own light.
Tritium sights are usually clearly marked with a Tritium symbol, such as "T" or "3H". See the front sight on my G26 below.
[ame]https://m.youtube.com/watch?v=Pr5OZhGXs00[/ame]