These heaters use tungsten filament heating elements that operate at high temperatures. The element is encapsulated in a quartz tube and coated with a special material designed to maximise the output of infrared heat. The offer very high radiant efficiencies and have short heat-up and cool-down time -- typically one second to achieve 90% output. Quartz tubes have an operating lifetime of typically 5,000 hours. The high temperature of quartz heaters elements means that they produce visible light which, in some circumstances, can be considered obtrusive. The most common quartz lamps produce a ruby glow. Lamps are also available that produce a golden rather than ruby glow. The quartz heaters in this category are designed for use outdoors and have appropriate IP (ingress protection) ratings. They can be used to heat smoking shelters or patios with much greater energy efficiency than is possible using gas patio heaters.