P      horizontal
S      the base of the lamp must be pointed downwards
SE    the lamp may be tilted in a certain direction
H      the base of the lamp must be pointed upwards

This code is essential since each type of lamp is designed for a specific luminaire or range of luminaires. The design of the lamp limits its use at various angles, for a number of reasons:

• The filament supports are not efficient at every angle and may weaken
• Heat given off by the lamp may damage the material used to adhere the bulb to the lamp base
• The tungsten particles recaptured by the filament during the halogen cycle are unevenly distributed, shortening the life of the lamp.