This 200 yard 40wt glow in the dark thread is activated by natural or artificial light! Ahrora thread has a 5 hour glow time after it charges for 2 hours in the sunlight. A great thread for decorative stitches, embroidery, quilting, costumes, and crafts! We recommend using our 80/12 topstitch needles with this thread if using a machine, or an embroidery needle by hand.