Passes the symbol is in the road traffic safety equipment the important one kind, establishes on the urban road and the road, by the shape, the color, the design and the writing constituted one kind of transportation language, provides the control to all road user, warns, to instruct, with the path direction information, played the vital role in the construction harmonious traffic order. The traffic signal passes on is one silent language, regards through the road user recognizes the read to obtain the information. In the daytime, has the sunlight to provide the sufficient degree of illumination, enables the traffic signal to have good regards recognizes the nature, but in the night, the traffic signal must maintain with the daytime same regards recognizes the nature, is mainly depends upon on the reference plane the retro-reflecting material to realize, therefore the retro-reflecting material performance's quality has decided the traffic signal directly at night function and the function