The electric lamp--particularly the modern, high-performance discharge devices, and the electricity to run them, of course. If you can't see the show, you don't have a show. Cliff Wilding, Lighting Engineering

Each time the filament was improved, life and wattage was increased, and it led to better fixture invention and design. We started the century with the carbon filament, with no fresnels, ellipsoidals, PARs, or moving lights. David Peerbolte, Peerbolte Creative

The introduction and ongoing development of compact tungsten filament lamps, which in turn made possible the use of precise optical systems in lighting instruments, and which in turn allowed the theory of the "spotlight era" to develop and the practice of the lighting art to flourish. Joel E. Rubin, Artec Consultants

While the arc light began a comeback in recent decades for most of the 20th century, the tungsten filament lamp provided most of the light by which entertainment design was seen. It produces much more light than the carbon filament lamp it replaced, while offering far greater convenience and control than its other 19th-century predecessor, the arc light. Eric Cornwell, lighting designer

HMI technology--For its impact on film, television, theatre, and theme parks. Metal halide lamps changed the way Hollywood lights its pictures, gave us fantastic followspots, moving lights that could take advantage of vibrant colors, you name it. Without the lamp, none of this would have happened. Ted Ferreira, lighting designer

The off-the-shelf pattern. It is interesting to note that it would have been impossible to develop the widespread use of the pattern (gobo), but for the ellipsoidal spotlight. The ever-present ellipsoidal spotlight made it easy for the designer to put a shadow pattern just about anywhere on the stage. The off-the-shelf stainless-steel pattern made it economically possible. GAM Products was not the first to introduce patterns; they were available in the 50s Century and Kliegl catalog, made from stamped-out radiator grille covers. Custom patterns were also made by either hand-cutting copper, brass, or aluminum, and later, by chemically milling stainless steel. However, it was the off-the-shelf availability of standard designs that changed the way the lighting designer related to this tool. It has become one of the most used tools onstage, third only to color filters and the light source itself. Joe Tawil, GAM Products

Optical lenses and reflectors--convex glass optical lens and parabolic reflectors are used in cameras, lighting, film projectors, etc. Eric Loader, Martin Professional