Being slumped over a keyboard in the same artificial lighting for hours on end, day in and day out, is going to harm your productivity more than help it. If you can, get outside in nature for a refreshing break. There have been countless studies on the benefits of being out in nature. Even just looking out of the window can freshen you up, while also giving your eyes a necessary break. Failing that, simply looking at an image of a natural scene can have similar calming effects, and help you focus.