**5.4.4 Mechanical characteristics**

Incandescent lamps are sensitive to vibration and shock. In addition to breakage of the glass envelope or the electrical feed-throughs, the filament structure is particularly fragile. As indicated above, electrical power should be applied gradually to avoid thermal shock.

The electrical and mechanical properties of a lamp change rapidly when a lamp is first used. Before a lamp is calibrated, it is usually aged by operating at the desired CCT for a period of time to enable the components of the lamp to stabilise, and to determine when the aging rate has stabilised. If measurements are made of the lamp output over time at a constant electrical operating current or voltage, the data may be used to estimate the change in the lamp calibration with later use.
