A Globar is used as thermal light source for infrared spectroscopy. It is a silicon carbide rod of 5 to 10 mm width and 20 to 50 mm length which is electrically heated up to 1,000 to 1,650 °C (1,830 to 3,000 °F). When combined with a downstream variable interference filter, it emits radiation from 4 to 15 micrometres wavelength. Globars are used as thermal light sources for infrared spectroscopy because their spectral behaviour corresponds approximately to that of a Planck radiator (i.e. a black body). Alternative middle-infrared luminous sources are Nernst lamps, coils of chrome–nickel alloy or high-pressure mercury lamps. The technical term Globar is an English portmanteau word consisting of glow and bar. Hence, the term glowbar is often used synonymously in the English-speaking area (which is an incorrect spelling in the strict sense). The American Resistor Company in Milwaukee, Wisconsin, had word and lettering Globar registered as a trademark (in a special decorative script font) with the United States Patent and Trademark Office on June 30, 1925 (registration number 0200201) and on October 18, 1927 (registration number 0234147). This registration had been renewed for the third time in 1987 (by various companies throughout 60 years).