Grow Light Controllers
Grow light controllers are fantastic - especially if you have multi-light rooms, or multiple grow rooms.
They don't just automate on/off times, but they have range of other features that allow you to get a tight control over your climate:
Sunrise & sunset mode: Lights gradually dim and boost over a period of time, rather than instantly. This is to ensure plants don't get shocked.
Temperature Control: With some controllers (like Parlux), you can dim and boost your output according to your grow room temperature. Others have a similar feature, called 'auto-dim', which automatically dims and eventually shuts off grow lights if your grow room grows too hot.
Smaller dimming increments: If dimming with a ballast, you normally only have 5 output options. With a controller, you can control your output in smaller increments and often have a larger output range.
Connect to other equipment: some grow light controllers have ECMs (external contactor modules) that allow you to connect and control other devices; like fans, CO2 equipment and heaters. If you're trying to create a closed loop room, this is ideal.