The Big Kahuna of all light sources is, of course, the sun. In terms of lighting homes or businesses, sunlight should be, as much as possible, included in an overall lighting plan - or scheme. The deliberate inclusion of natural light into a lighting plan is called daylighting. Optimally, artificial light is used as a compliment to daylight, providing illumination to places beyond the reach of natural light during the day, or instead of natural light after daylight hours.
It goes without saying that the more daylight can be routinely used in lighting, the lower the overall cost of lighting will be.