An HPS indoor grow light, used to start seedlings when it is too cold to leave plants outdoors, can be made with fluorescent light fixtures attached to a piece of plywood and hung at different distances from the plants as they grow. Young seedlings will need more warmth and so will need to have the grow lamp closer, while stronger plants may not need to have the lighting as close. Lamps should be set on a timer and left on most of the day and night to make up for the loss of sunlight.
Cut a piece of plywood 5 feet long by 3 feet wide. Place two 4-foot-long standard fluorescent light kit fixtures on the plywood so they are evenly spaced from each other.
Mark the plywood where the back insert of each fixture is. This is where the screws insert into the fixtures.
Take the fixtures off the plywood and lay them face down on the table in the same position they were in on the plywood.
Place the plywood on top of the fixtures exposing the marks on the back insert locations of the fixtures. Drill a pilot hole at each of the marks and screw a zip screw through the plywood into the back insert. Drill a pilot hole at each corner of the plywood and screw in an eye hook at each end.
Locate the studs in the ceiling by using an electronic stud finder that beeps when it finds a stud. Make the appropriate 4-foot-length measurements and mark the ceiling with a pencil where you intend to hang the plywood. Be sure these marks are on the studs to give the anchors and screws more strength to hold the hanging plywood and light fixture.
Drill pilot holes in the ceiling at the marks you made. Place heavily-ribbed plastic anchors in the holes. Screw in hooks through the anchors. Hang plastic and metal chains from the ceiling hooks with enough length so that they can be adjusted to different levels as needed. Attach the chains to the eye hooks in the plywood.
Insert the fluorescent bulb into the light fixtures. Plug the fixtures' electrical cords into an extension cord and connect the extension cord to an electric timer. Connect the timer cord to the power outlet. Set the timer for 16 hours a day to compensate for the low level of interior light (compared to that of natural sunlight).