A light bulb (1) with a base and inner vessel sealed in a vacuum-tight manner and surrounded by an enveloping part is provided with an adapter (13) at the end thereof made from ceramic polymer and fixed in a base insulator (12). The base insulator and the enveloping part are fastened to each other. The base insulator may be provided in pieces which fasten together and hold the adapter. The adapter allows cementless fastening of the inner bulb. The base insulator and the adapter part have matching indexing and mating indexing means for holding the base insulator and the adapter part in position relative to each other. Multiple mating indexing means on the base insulator allow the adapter to assume secure position at multiple heights relative to the base insulator.