When growing indoors we are replicating seasons using lighting on different time schedules, a lot of plants will continue to grow without flowering or fruiting under extended periods of light (usually 18 hours).  When the timing is brought down to 12 hours, the plants will assume the late Summer/early Autumn is arriving and its time to flower or bare fruit.  Controlling this is a vital part of a successful indoor crop.  If using T5, CFL, some lower powered LED or single 600w HID lighting then a simple mechanical heavy duty timer will suffice.  However, if you are using multiple HID lights you will need to use a Contractor.  Firing multiple HID lamps will cause a surge in electrical draw which will often fuse the pins in a timer leaving your lights permanently on or off and cause potential hazards.  A contactor such as a Greenpower Eco-switch is built to deal with these issues, absorbing the surge within its mechanics and ensuring it never reaches its in-built Graslin Timer.  Another benefit of using a contactor is that your lighting will in most cases only require 2 electrical outlets leaving others in the room available for fans, pumps etc without the need for hazardous trailing extension cables so often seen in Grow rooms.  We supply contactors built for 2, 4, 6, 8 and 16 lights.  Remember, most contactors will one rated for a number of lights – this is more often than not calculated on 600w light fixtures and the unit will have a total wattage load rating. If you are using 750/1000w fixtures then you will need to get a unit that is rated for the total wattage of your lights and not necessarily the number of lights.