found out that tyler,like most cities during the 40-50's started to use mercury vapor lighting,from 1949-1965 tyler was found to have abundand form109's and westy ov-20's,in 1965-1970 however a dark change brought an abrupt end to mercs in most parts of tyler,in 1970 form 109's and ov-20 were replaced with new high pressure sodium m-400-a powerdoors.