"If your ultimate goal is to decrease energy consumption, it may take more than just energy efficiency," Simmons said.
The Sandia scientists base their prediction on records dating back to 1700, which show that people have consistently spent about 0.72% of gross domestic product on lighting, regardless of the type of light source used. "There is this striking relationship between the consumption of light, its cost, and the wealth of nations," Tsao told environmentalresearchweb.
Much of the overall cost of light comes from the energy it uses; increased efficiency – or more precisely, better luminous efficacy – therefore lowers this cost per lumen unit of light output. However, if the cost of energy stays constant, continuing the historical trend would see increased light consumption countering the decreased energy consumption that LEDs would otherwise yield.
"Until now most people had constructed a baseline where the consumption of light that we have now won't change in the future," Tsao said. "In this paper we assume the future will behave like the past, rather than that the future will behave differently than the past."
While this situation casts a gloomy light on LEDs' eco-friendly credentials, the Sandia team emphasises that it does make them economically attractive. That's because, historically, increasing light consumption has helped economic growth, for example by allowing people to work by night or indoors. The Sandia researchers' work predicts that LEDs will continue to drive this trend. The productivity gained could add 1% to the world's per-capita GDP by 2030, compared to a scenario where fluorescent lights are dominant.
Improved lighting efficiency also provides options if energy prices should increase, either through supply constraints or carbon taxes. "If that happens and if luminous efficacy were to stay constant, the overall cost of light would increase," Tsao explained. "People would likely consume less, and in taking a hit on the consumption of light, they would also take a hit on productivity, which nobody wants. That's probably the biggest single argument against a carbon tax. But if a carbon tax materialized, the increase in luminous efficacy due to LEDs could help offset the loss of human productivity that would otherwise have occurred due to a loss of light consumption."
Despite previously authoring an enthusiastic forecast for LED lighting's energy savings based on current light-consumption levels, Fred Schubert believes that Tsao and Simmons' projections are convincing. The LED technology researcher, based at Rensselaer Polytechnic Institute, US, also reiterates the pair's message about energy prices. "The growth in the consumption of light cannot continue exponentially in the long term because our resources are limited," Schubert said.
Tsao, Simmons and colleagues reported their work in Journal of Physics D: Applied Physics.