Thermal shock resistance is the ability of a lamp and its materials, seals, and joints to withstand rapid temperature changes without cracking, leakage, deformation, or functional failure. It is verified under defined test conditions and should not be inferred only from the normal operating-temperature range. Rapid transitions can create different rates of expansion in glass, plastics, metals, adhesives, coatings, and electronic assemblies. Repeated stress may cause microcracks or loss of sealing even when each steady temperature is within the operating range. Tests therefore define the hot and cold temperatures, transfer time, dwell time, number of cycles, and pass criteria.