nm UV radiation to escape the lamp. This can cause the accelerated aging of some plastics used in the construction of luminaires, leaving them significantly discolored after only a few years' service. Polycarbonate suffers particularly from this problem and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp to have turned a dull, yellow color after only a short time. Uses Area and street lighting Although other types of HIDs are becoming more common, mercury vapor lamps are still sometimes used for area lighting and street lighting in the United States, Canada and Japan. UV curing Mercury vapor lamps are used in the printing industry to cure inks. These are typically high powered to rapidly cure and set the inks used. They are enclosed and have protections to prevent human exposure as well as specialised exhaust systems to remove the ozone generated. Molecular spectroscopy High-pressure mercury vapor (and some specially-designed metal-halide) lamps find application in molecular spectroscopy due to providing useful broadband continuum ("noise") energy at millimeter and terahertz wavelengths, owing to the high electron temperature of the arc plasma; the main UV emission line of ionized mercury (254 nm) correlates to a blackbody of T= 11,500 K. This property makes them among the very few simple, inexpensive sources available for generating such frequencies. For example, a standard 250-watt general-lighting mercury lamp produces significant output from 120 GHz to 6 THz. In addition, shorter wavelengths in the mid-infrared are emitted from the hot quartz arc-tube envelope. As with the ultraviolet output, the glass outer bulb is largely opaque at these frequencies and thus for this purpose needs to be removed (or omitted in purpose-made lamps). Projection Special ultra high-pressure mercury vapor lamps called Ultra-high-performance lamps or UHP lamps, are commonly used in digital video projectors, including DLP, 3LCD and LCoS projectors. See also History of street lighting in the United States List of light sources Ultra High Performance lamp References Further reading Museum of Electric Lamp Technology External links Articles containing video clips Gas discharge lamps Mercury (element)