By Jesse Emspak: Subscribe to Jesse's RSS feed
August 26, 2010 2:02 PM EDT
Light emitting diodes, or LEDs, are often touted as a greener alternative to light bulbs, but a study from Sandia National Laboratories says people may just use more light.
Jeff Tsao is a principal member of the technical staff at Sandia, and he looked at how much light people have used over time. He found that the number of lumens -- units of light -- that people use has steadily increased for three hundred years. Even though new technologies were more efficient -- gas lamps are more so than candles, for instance -- the response was to use more light at night rather than use less energy.
"Every time there is an increase in wealth, or income, and a decrease in cost of light, we consume more light," Tsao said. "In undeveloped countries similar things are going to happen. They are consuming what we may have consumed 100 years ago."
Tsao says he looked at consumption patterns in terms of the light used rather than the energy. He found the data from other economic studies, which tracked items such as whale oil imports (whale oil was once used in gas lamps) and candle sales. From that he was able to work out how much energy was used and how much light was produced.
He then plotted the use of lumen-hours per person. A 40-watt light bulb produces about 500 lumens, and a candle produces about 13. In the United Kingdom, people used less than 10 billion lumen-hours per year back in 1700. That sounds like a lot but it is less than 5 lumen-hours per day per person at the time -- which means on average people went through a small number of wax candles. Many went to bed soon after sunset, and only the wealthy had much light at all after dark.
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Tsao noted that the number of lumen-hours per year started to rise as new technologies, such as gas lamps came into wider use. But he also noticed that the amount of light used tended to follow gross domestic products rather closely. In the U.K., by 1900, most people used gas lamps, and the amount of light used was 10 trillion lumen-hours per year. The population was 38 million, and people used about 720 lumen-hours per day.
Today, the light use has grown to 100 times what it was in 1900, and using the numbers for the U.K. it shows people use 44,000 lumen-hours per day per person. That means on average a single person lights about nine 40-watt light bulbs for an hour each day.
The amount of light used has flattened out in the last few decades, Tsao said, primarily because the amount of energy per lumen hasn't improved all that much in that time. "It's basically been 40 to 50 lumens per watt for about 40 years or so," he said. LEDs increase that efficiently by a factor of two, so if they become widespread that further cuts the cost.
"There are a lot of things that could be playing into the increase in the consumption of light," Tsao said. "For instance, light isn't the only thing these new technologies give us. Moving to light bulbs meant freedom from smoke, and a light bulb is much less of a fire hazard."
But one thing he says is clear: there was a marked increase in light use, and if the future is anything like the past more efficient technologies -- reducing the cost of light -- will push people to use more.
One thing Tsao said might change that pattern is if the market for light is saturated. While he isn't sure that is the case, there are only so many hours in the day people can stay awake. Outdoor areas are not often lit that much, even in urban areas -- outside of heavy traffic regions such as the Las Vegas strip or Times Square, there really isn't all that much light used, he said.
But the counter to that is whether cheaper LEDs might make people use light in ways they didn't previously. Cheap electric lighting, for instance, made sporting events at night possible and increased the consumption of light per person. Some designers have talked about making clothing with glowing LEDs. "There are places where there's a whole new aesthetic, places where we didn't use light before," he said.
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