Illumination; reflectorization

All warning signs, and all regulatory signs, with the exception of pedestrian signs, urban parking signs and signs having a significance only during daylight hours, shall be illuminated or reflectorized so as to be visible during hours of darkness from all distances up to five hundred feet. All other traffic signs may be illuminated or reflectorized if desirable. All illumination shall normally be by white light, except that a flashing light incorporated in a sign installation shall be yellow when displayed with a warning sign or red when displayed with a stop sign, and shall be provided by means of: (a) A light, within or behind the sign, illuminating the main message or symbol, or luminous tubing shaped to the lettering or symbol; (b) An attached or independently mounted flood light or flood lights, directed on the face of the sign. Reflectorization of traffic signs shall reflect white light, except that if a reflecting coating is used as a background of a yellow sign it shall reflect yellow light, and shall be provided by means of: (a) Reflector buttons or units set into the symbol or message; (b) Reflecting coatings, either on the sign background or, where a black background or panel is used, in the symbol or message.