If you plan to add a dimmer, make sure it's compatible with the type of bulb you plan to use it on.
Some dimmers are for Incandescent/Halogen bulbs while others are made to control LED or CFL bulbs. Only universal dimmers are meant to control all types (as long as the LED & CFL bulbs are, in fact, dimmable).
You can read about which type of bulbs can be dimmer by each type of dimmer in the product descriptions.
Learn about Leviton dimmer types & bulb compatibility to find the right slide, rotary or toggle dimmer for your room.
Learn about Lutron dimming switches & compatible bulbs to select a Lutron brand dimmer switch.