Four-hundred-watt HPS (high pressure sodium) lights are used for providing nourishing light to indoor plants when no or little natural sunlight is available. Using artificial lights allows you to control vegetation and flowering without having to be limited or controlled by the seasons. Make sure to use a corresponding HPS ballast with your HPS bulb. Most ballasts can plug into standard outlets.
Hang the ballast above the plants. Ballasts usually hang with chains and can be secured with hooks on the ceiling or to a rack positioned over the plants.
Keep the light away from other surfaces, like walls or wood shelves, as they can get quite hot. Hang the light so it sits about 8 to 10 inches above the tops of the plants.
Use a plug-in electric timer so that the intervals of time that the light is on and off can be regulated and consistent.
Set the time for the lights to be on according to how much light the plants need during their vegetative stage. Light times will vary depending on the type of plants, but on average the light can be set to be on between 14 and 18 hours per day.
Keep adjusting the chain to raise the light as the plants grow.
Change the timer settings once the plants are ready to enter into a flowering stage. Again, this time varies depending on the plant, but usually this is 10 or 12 hours per day.