Projection lamp can't project without a negative. The pattern on the film is printed with ink, which belongs to organic matter and is easy to decompose and change color under strong light and high temperature. However, the projection lamp has strong light, which will produce high temperature during use, that is to say, it is used in lamps under high temperature and strong light. After oxidation discoloration, it is easy to make the color on the film fade, and the projected pattern will fade immediately within a few days, which is inconvenient for frequent replacement. The glass pattern adopts high temperature resistant coating, which is high temperature resistant. Even if the temperature of the lamp is bright and strong, there is no need to worry about the pattern change on the glass negative. Generally, glass negatives will change color obviously after several years of use, because the technology is complex and the cost is high.