Illustrated are the Form 4 and Form 5 fixtures offered by GE which housed the then-new enclosed arc lighting system. The latter meant less frequent arc light carbon maintanence (weekly instead of daily compared to the old "open arcs") as well as better luminous efficiency. About 1912 the introduction of revolutionary gas-filled, coiled-coil tungsten-filament incandescent lamps quickly made most area-lighting arc lights obsolete. For many years after then, GE and others offered retrofit kits whereby the shown fixtures could be easily converted to this much more efficient and longer lasting light source (which has remained pretty much unchanged!).