A transparent lighting device used as a main lighting device in mines. Its
distribution characteristics are simple, since there is no control of light
other than that provided by the interior of the upper part of the fitting,
which absorbs a large proportion of the upward flux component from the lamp and
reflects the remainder. It is usually to be found spaced at intervals of 20 to
50 ft (6.1 to 15.2 m), 6 to 7 ft (1.83 to 2.13 m) high, along the centerline of
roads 12 to 14 ft (3.66 to 4.27 m) wide. In general, the most noticeable effect
of such a layout is glare. Roberts, 2
Source:
Dictionary of Mining, Mineral, and Related Terms
