We recommend that you give us a call if you are not sure what lamp to order. The shape alone does not tell you what technology (HPS, Metal Halide, Pulse Start, etc.) you need to purchase for your fixture. The quickest way to find out what lamp you need is to find the ANSI code on the ballast sticker and let us know. This code will match the lamp that is designed for the fixture. The lamp and ballast must have matching ANSI codes or the fixture will NOT work.