Will Greener Lighting Save Energy?

I feel reasonably sure that we all, by now, have heard some of the urging to reduce our energy consumption, and thereby indirectly help reduce emissions of carbon dioxide.  One of the steps that has been widely recommended, at least here in the US, is to substitute more efficient light sources (such as compact fluorescent lamps) for our traditional incandescent light bulbs.  (Most of the energy used by incandescent bulbs is given off as heat.)  There has also been an expectation (I wrote about it earlier) that further development of light-emitting diodes (LEDs) could give us an even more energy-efficient source of light.    There has been a more or less common but unspoken assumption that people would just switch to the new lighting technologies, thereby saving energy, with nothing else changing.

Now this is a somewhat curious assumption to make from an economic point of view.  If there new lighting devices save energy, that will manifest itself as a lower cost per unit of light obtained.  (Of course, one must account for the total cost of light production, including the purchase of the device, but at least the possibility of net savings exists.)   For most goods that people buy, a drop in the price per unit will tend to produce an increase in the number of units consumed, other things being equal.

This week’s edition of The Economist has an article reporting on a new analysis[abstract] published this week in the Journal of Physics D by a groups of scientists at Sandia National Laboratory [full paper PDF free download for 1 month].  (The PhysOrg.com site also has an article on this.)  The authors examine the history of lighting technology improvements, and find that better, and cheaper, lighting technology has generally produced an increased demand for lighting.  As The Economist puts it,

The light perceived by the human eye is measured in units called lumen-hours. This is about the amount produced by burning a candle for an hour. In 1700 a typical Briton consumed 580 lumen-hours in the course of a year, from candles, wood and oil. Today, burning electric lights, he uses about 46 megalumen-hours—almost 100,000 times as much. Better technology has stimulated demand, resulting in more energy being purchased for conversion into light.

If you have ever tried to manage after dark by candlelight when the power is out, you will probably have gained some appreciation that the artificial light levels we are used to today are rather higher than those expected a few generations ago.

The paper itself is a very good piece of work.  It looks at how lighting consumption has changed as new technologies for producing artificial light have been introduced.   Interestingly, using data from a collection of studies, the authors find that the proportion of world-wide gross domestic product per capita spent on artificial light has remained nearly constant, at about 0..71%.   As the article points out, this is not a perverse result: people don’t do this because they are gluttons, but because the greater availability of useful lighting makes them more productive and brings other benefits, such as being able to read at night.

The authors also develop a model to forecast what the net effect of introducing LED lighting might be.  Using the assumption from current technology forecasts that, by 2030, LEDs will be about three times as efficient as current compact fluorescent lamps, their model predicts that per capita artificial light consumption will increase by about 10× over the same period.  But they also point out some possible ways in which this increase might be mitigated; for example, since LEDs are solid-state electronic devices, it should be possible to control both the amount and color temperature of the delivered light in a much more precise and localized way.

The paper is a good example of trying to think through all the implications of a technology change; it is well worth a read.

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