This Delta Glow in the Dark Tape (1" x 5yds) is non-toxic and contains no radium. Recharges in 10-15 seconds after any exposure to any light and glows for hours. Safe in all darkrooms (color or black and white). Use only 1/2" squares placed every 4 ft. in color darkroom. For indoor or outdoor use. Pressure sensitive adhesive holds fast to most non-porous surfaces.