Source:
http://www.bulbconnection.com/Definitions.cfm
Orientation (also Operating Position or Burn Position)
Mercury and High Pressure Sodium lamps may be operated in any burn position and will still maintain their rated performance specifications. Metal Halide and Low Pressure Sodium lamps, however, are optimized for performance in specific burn positions, or may be restricted to certain burn positions for safety reasons.
U = Any, Universal -> Universal burning position
BD = Base Down
BD30 = Within 30° of Vertical Base Down
BD45 = Within 45° of Vertical Base Down
BDTH = Base Down to Horizontal
BU = Base Up
BU ±15° = Base Up Within ±15°
BU30 = Within 30° of Vertical Base Up
HD = Horizontal Down
Horiz ±10° = Within ±10° of Horizontal Position
Horiz ±15° = Within ±15° of Horizontal Position
Horiz ±30° = Within ±30° of Horizontal Position
Horiz ±4° = Within ±4° of Horizontal Position
Horiz ±40° = Within ±40° of Horizontal Position
Horiz ±45° = Within ±45° of Horizontal Position
Horiz ±60° = Within ±60° of Horizontal Position
Horiz ±75° = Within 75° of Horizontal Position
Horizontal = Horizontal
p20 = Within ±20° of Horizontal Position
p90/15 = Horizontal Down
s30 = Within ±30° of Vertical Position
s30 p20 = Within ±30° of Vertical Position, or Within ±20° Horizontal Position
s45, anode down = Within ±45° of Vertical Position, Anode Down
s90 = Within ±90° of Vertical Position
VBD = Vertical Base Down
VBU = Vertical Base Up
Vert ±10° = Within ±10° of Vertical Position
Vert ±15° = Within ±15° of Vertical Position
Vert ±30° = Within ±30° of Vertical Position
Vert ±4° = Within ±4° of Vertical Position
Vert ±45° = Within ±45° of Vertical Position
Vert ±5° = Within ±5° of Vertical Position
Vert ±90° = Within ±90° of Vertical Position
