Radial Waves were some of the first electric enameled street lights from the early 1900's and were used up to about the 1950's. They often have cast aluminum heads or cast iron heads with porcelain insulators. Almost all are 20" diameter and have flat ruffled bottoms. Common color is green, sometimes light gray. Rare colors are blue or black. The most sought after Radials are those with the porcelain insulator on top. btw, these make killer outdoor home lighting...