A room can look darker, and the light dingier, simply because the bulbs and fixtures have attracted dust. This is especially true with some light fixtures that have texture or holes in them. Cleaning them will allow the light to shine brightly once again.
First, ensure the light has been turned off for at least an hour. You don’t want to risk burns, or damage the bulb, by cleaning when it is still hot.
Dust the bulbs with a clean cloth, dampened with water if needed. Do not use any chemicals to clean the bulbs.
Clean the fixtures. If they are simple rounded fixtures, you can even take them to the sink and clean them with soap and water. Delicate fixtures can be cleaned gently with a dampened cloth, or a bit of soap if they are especially dirty. If the dome style has accumulated bugs or larger dust bunnies, you can even vacuum it up first before cleaning.