Luminary GLOW IN THE DARK thread is a luminous thread after being exposed to light will glow up to eight hours. Luminary’s consistent elongation & high tensile strength offer optimal performance that is consistent. The glowing effect is diminished after each wash, ironing & dry-cleaning session. Luminary has successfully passed 50 wash tests while still retaining some of its glowing power. It’s 40 weight and 700 yards.