Light is essential for human life. Modern societies have created homes, schools, and workplaces that rely on electric light sources. Some of the electricity used to generate the light in these spaces is wasted, largely owing to ignorance. The efficient application of electric, as well as natural, light sources to the human condition is a sophisticated effort, but one that is essential to a sustainable and enjoyable future.

What Is Light?

Humans are a diurnal species, which means that we are active in the day and asleep at night. Indeed, daylight is the primary stimulus to the photobiological system that regulates our sleep-awake cycle. Of course, while we are awake, we see, and we depend a great deal on seeing. Approximately 80 percent of the human brain devoted to sensing the environment is devoted to vision. It is not surprising, then, that from the beginning of human history we...