Refers to a flat thread that has a subtle glow when exposed to light. This thread type is  identified with an 'F' after the colour number, as in 051F. Use these  threads for Halloween motifs, children's  projects, tropical fish, moons, stars, or any whimsical design. The  length of time the material will glow depends upon the length of time the material is exposed to direct light. For example, five minutes of direct light equals approximately 10 to 15 minutes of glow time. They are ideal for decorating clothing, but should not be used as a substitute for safety-rated reflective material for visibility at night.