Step 1: The joints
Just cut four cylinders from an old broom handle, length could be about 4 cm.
Then you need a small wood board, at least 1 cm thick.
Make 6 mm holes in both ends of the cylinders, and also on a side of the board.
I've also glued on the bottom side of the board a rectangle of rubber of the right dimensions, to improve the adherence on any surface.
One of the cylinders has two little hole instead of a big one, they're to screw the spotlight holder, so measure the screws stem to find the right diameter. The groove made with a file is not essential, but it keeps the wood far from the hot glass of the lamp.
Step 2: The bars
Cut four pieces from them, and bend them at these shapes you see in the picture. There is no need to be very accurate, just be sure to have about half length of the wood cylinders before the fold.