If you have access to a broken LED TV or monitor, or in some cases CFC, you can just buy these. Search for "led panel light", and you can find them in all sorts of sizes.<p>I was looking at building one last winter, but on CraigsList people tend to overestimate the worth of a TV with a broken screen. "Awesome 4K TV, paid $1200 3 months ago, just need to replace broken screen, $250." You gotta talk them out of that with a "A new panel costs more than buying the whole TV."<p>You can also buy just fresnel lenses on Amazon, but then you gotta build the and line it with foil.