The best way to brighten your day is sunshine. Since many of us spend the brightest hours of the day indoors, we need to find ways to let the light in.
The best improvement I made to my office was putting solar tubes in any room that did not have a window. Solar tubes are easier to maintain than skylights and don’t seem to allow any energy loss. Actually the energy savings from not turning on the lights most likely exceeds any heat/cooling loss.
I can walk through my entire office and never turn on a light because every room, including the warehouse has natural light pouring in. So on those days that I come to the office when no one is here because I like the solitude, I can walk around without flipping a switch. (All you entrepreneurs know that Saturday morning feeling of wondering around your office alone…just because)