The combination of four way switches and three way switches makes it possible to control a set of lights from three or more locations. Four way switches have four terminals and do not have ON-OFF marking, this switches are always installed between a pair of three way switches. Four way switches are usually used in large rooms that contain multiple areas.
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The dimmer switch adds a decorative touch to any light installation. Dimmers should not be used with compact fluorescent lamps unless the light is specifically designed for dimming, and most LED lamps are possible for dimming. Dimmers are available in both the single pole and three pole switch style.
We can use the three way switches to control lighting fixture from two locations, and these switches are always installed in pairs, so many people think it of as a two way switch. The three way switch has 3 terminals on it: a “common” terminal and two “traveler” terminals, and do not have ON-OFF markings. The three way switch works by keeping power at all times to one of the traveler terminals. This lets you turn the power on and off at either switch location. It’s common for people to miss wire these switches when changing them out for more decorative style switches. Three way switches are typically used in stairwells, halls and in rooms where you have more than one entrance point.