The Lumii Grow Light Timer/Contactor is suitable for timing 1 x 600w HID ballast or up to 6 x 200w CFLs. It is very reliable and has a high quality timer unit with a robust 'inline' case design with socket and timer dust covers.
Normal household timers are not built to take the high inductive loads produced by HID ballasts. If used with an HID ballast, the contacts inside the timer that open and close the timed circuit will overheat and weld together, breaking the timer and leaving your grow lights permanently on.
The LUMii Heavy Duty 24 Hour Plug In Timer is different – as the name suggests it is designed to take high loads and has no problem dealing with the inductive loads produced by a 600 watt ballast. This means no separate contactor is required, saving you money. There are 96 switching operations within a 24 hour period (every 15 minutes). Heavy duty contacts mean it can take high inductive loads.