Ordinary incandescent lamps (non halogen lamps) subject to wear. They should be replaced once every 2 years, even if they are still working. An incandescent lamp with reduced brightness is identified by black deposits on the lamp bulb.
Switch off the corresponding consumer before replacing the lamp.
Attention: do not touch the lamp bulb with your fingers. From fingerprints, it becomes cloudy and - due to heating - a deposit forms on the reflector, which darkens the reflector. Be sure to replace the lamp with a lamp of the same type. Wipe stains on the lamp bulb with a clean, lint-free cloth and alcohol.