Using 1 x 6 inch planks, build a three-sided box beam the length of the wall where the valance will be mounted. Be sure to make it slightly shorter, perhaps an inch, so that it can easily slide into place. With the boards cut to length, stand two of them on edge, lay a bead of glue, and place the third on top, making an upside-down "U." Nail through the top board into the side pieces. Use a pneumatic nail gun, hammer or screws, but be careful not to split the wood.
Add interior supports. These can be L-brackets or pieces of wood cut to fit inside the beam. Put notches in the wooden supports to leave space for the mounting board and the light cords. Do not put a support where a light will be.
Purchase small, round under-cabinet lights. Make sure that they can be used with a dimmer.
Using a hole saw of the diameter specified in the instructions that come with the lights, cut holes where the lights will go. With the valance turned on its side and the open end facing the wall, the lights should be mounted on the underside.
Directly above the hole for each of the lights, drill three or four small ventilation holes.
At the end of the valance where the cords will come out, make a small notch at the bottom corner.
Paint the entire valance.
While the paint is drying, mark a level line on the wall 3/4 of an inch below where the top of the valance will rest. Four inches below that line, mark the stud locations on the wall.
Cut a piece of 2-by-4 about 2 inches shorter than the length of the valance. With the board lying flat on the wall, line up the top of the 2-by-4 with the line drawn on the wall and screw it into the studs.
When the valance is dry, mount the lights in the holes and run all of the wires to one end. Use extension cords if the ones that come with the lights are not long enough. Test the lights and make sure they are all working.
Slide the valance over the 2-by-4 and screw down through the top of the valance into the 2-by-4. Be sure not to hit the cords.
Attach dimmers to the cords and plug in the lights.
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