Ok, random yes, but they do have some theatrical ties: All questions refer to American-style, traditional, 3 color, incandescent, non-LED traffic lights. What are the two common diameters of traffic lights available? What type of reflector is used in a traffic light? What type of glass lenses are commonly used? (I'm looking for a more blanket term here, as there are several different varieties of lenses from the past and the present, however, for reference, there are about 2-3 dominant styles) What is the official name for the "blue green" color seen on some traffic lights? Where did this color originate and why was it needed? What might we call the two styles of visors found on traffic lights in the theatrical world? Before LED's, how was the "green arrow" produced? Well, have at 'em.