p. A designation specifying that the lamp should be operated with the bottom (base
) of the lamp above
. Non- tungsten-halogen
lamps were particularly finicky about orientation, due to how the coils of the filament were supported.
There is usually a number following, giving maximum deviation
from vertical. Thus BBU45 (or BU45) means base up +/- 45 degrees. The BBU lamp was/is used in the radial
ERS, and is in fact the reason for the lamp penetrating the reflector
in a non-axial
location. With the fixture
above and pointing 45° downward, the lamp is vertical.
For the opposite, see BBD
With today's modern lamps, it's an unnecessary specification, as almost all T/H lamps allow "burn in