Ultraviolet Hazards
All mercury vapor lamps (including metal halide lamps) must contain a feature (or be installed in a fixture that contains a feature) that prevents ultraviolet radiation from escaping. Usually, the borosilicate glass outer bulb of the lamp performs this function but special care must be taken if the lamp is installed in a situation where this outer envelope can become damaged. There have been documented cases of lamps being damaged in gymnasiums by a ball hitting it. Sun burns and eye inflammation have resulted. When used in locations like gyms, the fixture should contain a strong outer guard or an outer lens to protect the lamp's outer bulb. Also, special "safety" lamps are made that will deliberately burn out if the outer glass is broken. This is usually achieved by using a thin carbon strip, which will burn up in the presence of air, to connect one of the electrodes.
Even with these methods, some UV radiation can still pass through the outer bulb of the lamp. This causes the aging process of some plastics used in the construction of luminaires to be accelerated, 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, 'ear-wax'-like color after only a short time. Certain polishes, such as Brasso, can be used to remove some of the yellowing, but usually only with limited success.
Read more about this topic: Mercury-vapor Lamp
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