 There have also been electronics that stick onto the end of the screw base and allow the attached lamp to flash, for example, to attract the attention of arriving guests or emergency vehicles; others function as a dimmer or timer, or dim gradually in a child's bedroom in the evening.Some thermionic valves vacuum tubes, such as certain rectifiers, use an Edison screw base.Three-way lamps have a "d" suffix to indicate double contacts, usually E26d or E27d, or rarely E39d.