A coloured fabric or other flexible material impregnated with dyes that absorb radiation from one source and emit it again as visible light, so as to appear bright and glowing. For the purpose of compliance to the Lighting and Marking Regulation, the flags must have an area not less than 0.2 m² (320 in.²) and be mounted such that the full area is visible to traffic approaching from the front or rear. Suggested colours are orange and red.