Cut a piece of 3/4-inch thick plywood 12 inches wide and long enough to give each dimmer 5 inches of space. Using a light switch junction box as a tracing template, mark a hole for each dimmer, evenly spaced across the plywood. Use a jig saw to cut these holes out. Fit a junction box into each hole in the plywood and attach each box with a 3/4 inch wood screw through the tab at the top and bottom. With a screwdriver, tap out the top and bottom punch-out on each junction box.
Cut one 8 foot heavy duty 12 gauge extension cord in half for each dimmer. Cut the casing back about 3 inches from the end of each half with a utility knife. Use a wire stripper to strip the insulation from each of the three wires. To strip the insulation, insert the wire into the correct notch in the stripper one inch from the end of the wire and clamp it closed, pulling toward the end of the wire.
Feed the cable of the male ends into the bottom holes of the junction boxes and the female end through the top. Attach the wires, one set for each dimmer, to 500 watt household sliding dimmers. Attach the black wires to the silver screw, the white wires to the gold screw and the green ground to the green screw. Tighten the screws with a screwdriver. Fit each dimmer into a hole in the board and attach with a screw through the top and bottom tabs.
Fit face plates over each dimmer and tighten the screws to hold them firmly in place. Plug the male ends into extension cords and run each cord to an outlet, no more than two plugs for any one circuit. Run extension cords from the female ends and connect them to your lights. Each dimmer can power up to 500 watts of light safely. This can be one 500 watt fixture, or any combination of lights up to 500 watts. Turn the lights on by sliding the dimmers up to the desired level.