Dirk Hanson, writing for Nautilus:
[Sandia National Laboratory physicist Jeff] Tsao calculates that, as a result, light represents a constant fraction of per capita gross domestic product (GDP) over time; the world has been spending 0.72 percent of its GDP for light for 300 years now. […]
The Sandia group forecasts that “the developed countries are nearing a saturation point in average illuminance, but plausible arguments can be made that the saturation point may yet be a factor of 10 or more higher.” Even a factor of 10 is small compared to the distance we’ve come, and may be reached in the not-too-distant future.