Windows, until the development of cheap and effective glass manufacturing, were originally small things that weren’t much more than holes in the wall. Their usefulness had to be balanced between the amount of light they let in and the amount of heat and smoke they let out. Yet in situations where money was no object, as in the construction of the great European cathedrals, windows could be used for illumination far more effectively (and beautifully) than any other form of light. As the technology developed, the construction of the window-rich stately old homes of England (particularly Hardwick Hall, "more glass than wall" as the saying went) in the 1590s set architects on the path of bringing more sunlight into the home.
The widespread development of natural gas lighting around the 1820s, followed 60 years later by the gas mantle (a piece of radioactive thorium that when heated by a gas flame glowed brighter than the gas flame itself) were the last hurrah of the large scale burning of things to produce light. To the jeers of "Judas!" from gas lamps everywhere, in the 1880s indoor lighting went electric.
But Thomas Edison’s invention still didn’t separate light from heat. The incandescent lamp worked by running a current of electricity through a thin tungsten wire until it glowed. The bulb gave off light, but only as a by-product of the enormous amounts of heat created; to this day, incandescent lamps convert, at best, only three percent of their energy to visible light. The sale of fluorescent lights in the 1930s brought a slightly cooler method of producing light, but it has only been comparatively recently that cold light has moved from the lab into the home.
Now we’re in the midst of a revolution in interior lighting: New technologies to produce light are being developed and—at least in America, where lighting accounts for approximately 9 percent of America’s electricity use—they all may soon be regulated by the American Clean Energy and Security Act of 2009. Section 211 of that bill calls for all electric lights manufactured after 2014 to output at least 80 lumens per watt of electricity—an efficiency many times greater than today’s incandescent lightbulbs! But that’s only part of the story. For the foreseeable future, our houses will still be lit by a variety of means, including high-tech spotlights, direct or indirect sunlight, and, from time to time, even the simple candle.