The image above is a portable galvanized steel egg candler that was manufactured sometime after 1922.
The egg candler was used by sanitarians to determine the quality and grade of the egg. By looking at the egg’s air cell, the yolk, and the albumen (i.e., egg white), sanitarians were able to determine whether the egg should be graded AA, A, B, or inedible. An excellent description of the egg inspection process is found in the Sanitarian’s Handbook: Theory & Administrative Practice for Environmental Health published in 1977 by Dr. Ben Freedman.
The egg candler was standard equipment when inspecting farm vendors, egg wholesalers, and egg breakers.
The candler pictured above has the original bulb and is insulated with asbestos. The keyless porcelain socket was manufactured by the Knox Porcelain Corporation of Knoxville, Tennessee. The carrying handle has two screw keyways that allow it to be temporarily mounted to a wall.