Iron topped SL (side lit) also known as a Workmans lamp. Workmen were not allowed ro relight underground. The lamp was lit in the lamp room or at an underground lighting station. The lighter was a green electric box about 9″ square. A 4/5 volt current is applied to the tin glass plate and the vessel, the circuit via several insulating washers passes through the platinum wire adjacent to the wick. When current is applied the wire glows red lighting the Colzalene fuel. Look for a 2 digit number stamped into the brass ring around the bottom of the glass, 57/ is made in 1957.SL’s were around from the 1920’s through to the early 1980’s. The iron tops were replaced in the 1960’s with stainless steel.