This lamp with 2 part opaque glass shades with floral decoration and brass base and mounts is referred to as a 'Gone with the Wind' lamp. From the shape of the metal base, yours was likely produced by Pittsburgh Glass. This dates to just about 1895-1900. It was originally made as an oil or kerosene lamp and has since been converted to electric. Converting an oil lamp to electric was popular in the 3rd quarter of the 20th century, however it does impact the value on today's market; collectors prefer original condition. The estimate is based on actual past auction sale records of comparables.