Luminaires using which type of lamp installed in areas subject to physical damage must be protected by a lens?

Luminaires that use mercury vapor lamps must be protected by a lens when installed in areas subject to physical damage due to several factors associated with the nature of the lamp and its components. Mercury vapor lamps contain hazardous materials, such as mercury, which poses risks in case of the lamp breaking. The lens serves as a physical barrier to prevent shards and hazardous materials from dispersing in the event of damage.

Additionally, these lamps are often used in outdoor applications and environments where they may be exposed to impact or vandalism. The lens not only ensures safety but also helps maintain proper coverage and efficiency of the lighting by reducing glare and focusing the light output effectively.

While LED, incandescent, and halogen lamps also have their own safety considerations, they do not generally carry the same level of risk concerning hazardous materials or require the same stringent protection in typical areas subject to physical damage. Thus, the specific requirement for lenses in areas prone to impacts is particularly relevant for luminaires with mercury vapor lamps.