The Trex Motion Controller is a powerful addition to any lighting project. It puts you in control of how and when your lights come on, and has unique features not offered by other controllers. This 1-3/4 inch diameter controller can be used to replace the timer and dimmer, and it adds the functionality of a motion controller. Using the supplied remote, the installer can program several aspects of the lighting system to get a perfect setup. The photocell sensor is the key element for control, once it senses darkness it will activate the lights for the exact amount of time you need them on. Have to put the sensor somewhere that doesn't receive full sunlight No problem, the photocell sensitivity is adjustable to compensate for less-than-ideal conditions. You can also have your lights come on when the controller senses motion. The sensitivity of this sensor is also adjustable, in the event unwanted motion is causing the lights to activate. Lastly, this little device can also dim the lighting circuit to make it one of the most complete low-profile controllers available in outdoor deck lighting. So get rid of that bulky timer on the top side of your deck and take control of your lighting system!