Privately owned passenger cars used for home delivery of commercially prepared food may be equipped with one steady-burning white light for the nighttime illumination of a sign identifying the business delivering the food. Such sign shall not utilize primarily green, red or blue colors. Such sign shall not exceed eighteen inches in height nor have more than four sides, no side of which shall exceed fifteen by twenty-four inches. Such light shall emit diffused illumination of such an intensity as not to project a glaring or dazzling light. Such light may only be illuminated during delivery.