ABSTRACT
The lighting of interior spaces evolved over millennia from only daylight and firelight sources to increasingly complex uses of both, and finally to electric light replacing fossil fuel-based light in the early 20th century. As architecture became more complex, buildings became better at using available daylight to provide ample light indoors, and as fuel-based light sources evolved, then became more efficient at producing light, light became whiter. Since the introduction of electric light, interior lighting has evolved from a standard practice of one lightbulb in the ceiling into a more sophisticated approach with different layers of light. This evolution has been accelerated and improved with the introduction of LEDs, which are much more flexible, efficient, and adaptable to different residential lighting applications than incandescent light sources.
