Fun Fact! Diffused light, like through a cloth in a light box, doesn't really work for charging glow in the dark. Use direct light.
This is purely a "for fun" addition to your models, but it's kinda neat being able to add some character to your army. It's also neat to be able to say things like, "All my magic stuff glows in the dark," or "My underwater 3D game board is bullet proof."
This stuff is also available at most hobby stores for pretty cheap. However, there are a bunch of places online that sell high-end glow in the dark paint and pigments. (powder) It's stronger, brighter and comes in other colours, but it's expensive. Price is high mostly because it's meant for large projects and comes in big containers, but sometimes you can find smaller "tester" kits.
Not to be confused with day-glo stuff... aka, paints and pigments that are so bright (usually neon) that they look intense under normal light. (But don't actually glow)
The paint itself is basically clear. On the right, you can see a photo where I've used it on my Voidwalker Krielstone Bearer and there's no difference in how the runes look. (I added this paint after varnishing.. I'd suspect that the glow wouldn't be as strong through the varnish.)
Below you can see a photo of the runes glowing in the dark. The left photo is the original, but the camera didn't pick up the glow very well. In person, they glow a lot stronger, so the pic on the right is me fiddling with the brightness levels after.
