Treehugger asks if LED lighting is more efficient than daylight. It seems like a dumb question at first because isn’t daylight free? But the problem inside buildings is that windows allow heat to come and go in addition to light, and LEDs have gotten so efficient that it is not an easy question to answer whether bricking up a window and replacing the light with LEDs would be more or less energy efficient. They conclude that windows should be designed with human comfort and happiness in mind.