Making better use of natural daylight can reduce a home’s lighting energy use by around 20 percent simply by opening things up.
Rearrange rooms so desks and seating sit near windows, since tasks done in daylight need no lamp.
Use light-colored walls and mirrors to bounce daylight deeper into a room, which multiplies what the window provides.
Keep windows clean and curtains open during the day, and add dimmers so artificial light is only a supplement.
Free daylight is the cheapest energy there is, and the easiest to overlook.