Quartz infrared heating elements emit medium wave infrared energy and are particularly effective in systems where rapid heater response is required. Tubular infrared lamps in quartz bulbs produce infrared radiation in wavelengths of 1.5–8 μm. The enclosed filament operates at around , producing more shorter-wavelength radiation than open wire-coil sources. Developed in the 1950s at General Electric, these lamps produce about () and can be combined to radiate 500 watts per square foot (). To achieve even higher power densities, halogen lamps were used. Quartz infrared lamps are used in highly polished reflectors to direct radiation in a uniform and concentrated pattern.