Light timers are a crucial piece of equipment if you are using grow lights. Plants have varying light requirements and the time they need the lights off very likely does not coincide with your own sleep!
This is where timers come in. Timers can vary from simple analog devices to more expensive and capable digital timers.
Some timers come with a manual override feature that allows the lights to be turned on and off without affecting the programming. If, like my parents, you live in an area that is prone to power failures, look for a model that doesn’t lose its programming when the power goes.
Some timers can switch lights on and off multiple times per day. This can be useful if your grow lights are somewhere where you spend time and it disturbs you during certain hours (e.g. while watching TV). Rather set them to switch off during the times that you’re likely to watch TV.
Make sure that the timer you choose is rated at a high enough amperage to support the lights it will control.
Some timers will allow you to vary the timing for each day of the week while others only allow a day to day setting.