Editing Metal-halide lamp (section)

===Outer bulb===
Most types are fitted with an outer glass bulb to protect the inner components and prevent heat loss. The outer bulb can
also be used to block some or all of the [[ultraviolet|UV]] light generated by the mercury vapor discharge, and can be composed of specially doped "UV stop" fused silica. Ultraviolet protection is commonly employed in single ended (single base) models and double ended models that provide illumination for nearby human use. Some high-powered models, particularly the lead-gallium UV printing models and models used for some types of sports stadium lighting do not have an outer bulb. The use of a bare arc tube can allow transmission of UV or precise positioning within the optical system of a [[luminaire]]. The cover glass of the luminaire can be used to block the UV, and can also protect people or equipment if the lamp should fail by exploding.