DAYLIGHT IS FREE
Daylight, with its high luminous efficiency of 90 to 110 lumens per watt of radiant power, is available to us completely free of charge. The clever use of this practically inexhaustible energy resource in buildings reduces the time we need artificial light (and heating) and thus lowers capital and operating costs.
In addition, sufficient daylight increases our sense of well-being and alertness. This, too, is often a cost factor.
Accordingly, if we were to consider daylight as a material good, we could all be considered rich individuals. Daylight is thus probably the most democratic light source in the world.