Although there is a vinyl that actually “glows in the dark”, it is designed for interior use only.
What most people are referring to when they are seeking vinyl lettering for night time visibility is reflective vinyl.  Reflective vinyl is the same type of vinyl used on STOP signs and other street signs. Reflective vinyl graphics “light up” by reflecting light back at night such as when your headlights shine on a STOP sign.  Without a light source though, the reflective vinyl has no light to reflect back and remains dark.  Therefore, if you use reflective vinyl letters for a stationary sign that either won’t catch the headlights or is not lit with exterior lighting, it will NOT be seen.  So there‘s no point in spending the extra money. Since reflective vinyl letters are 74% brighter to the human eye than non-reflective vinyl graphics, they can add extra punch to a sign at night that has exterior lighting.  High-Performance Reflective Vinyl Graphics are durable outdoors 7-10 years.