Avoid the many vendors selling cheaply made car tail light bulbs that claim they will work in film viewers. These always result in dim pictures! The Hama bulb is made specifically for film viewer optics for the brightest incandescent image you can get. The key is a higher quality filament of specific shape used for microscopes and other optical specific equipment. Fits all 8mm viewers (Elmo, Goko, Vernon, etc) with standard BA15S bayonet socket.