It depends on the size of the screen. I have 2 screens 32 & 34 inches (so relatively large). That's why I ordered two. With 2x 24s it works theoretically if you only use one, but then one side is darker (i.e. the one without light). I would recommend two, as I am quite happy with my lighting result, and I would recommend the Screenbar PLUS, as the operation with the wheel is much better than with the standard Screenbar.