For Lighting, Sustainability is within Reach: But is demand saturated?

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In 2006 when the first Annual Energy Outlook was released by the Department of Energy, electricity dedicated to residential lighting was expected to continue growing at a consistent (if slow 0.3% per household annually) rate (red line below). Instead the electricity the average household is using for lighting has fallen by 18%!1)The AEO’s most recent measured numbers are two years older than the report’s year, so this change is from 2004-2012 The even better news is that this is just the beginning of what is expected to be a huge fall in the demand for electricity to light our homes.

The above graph shows the Department of Energy’s latest projections of electricity demand per household for lighting compared to their original projection.2)As with most trends, population/household growth should be taken out and the trend analyzed on a per capita basis, so I used the AEO’s data to do that and plotted the results here. They project a further drop of more than 60% between now and 2040. The UK government projects a similar scale drop in demand to happen by 2020. What is causing this dramatic change, has everyone started turning off the lights?

Is demand for lighting saturated?

For most of human history our access to lighting was extremely limited–a fire in a hearth for most and the flickering light of candles for those wealthy enough to afford them.3)Well over a billion people in the world are still in this situation. Yet humans clearly contain an innate desire to light their homes and as technology made lighting available and increasing wealth made it more accessible, people have vastly increased the amount of lighting they use. Fouquet and Pearson (2006)4)Fouquet, R. and Pearson, P. (2006) “Seven centuries of energy services: the price and use of lighting in the United Kingdom (1300-2000).” The Energy Journal 27(1) 139-77. traced this trend within the UK and graphed the results for the last three hundred years.

Consumption of Lighting in the UK over the last 300 years

The use of the logarithmic scale disguises the sheer size of the increase in lighting (in this case referred to as lumen-hours, which is a measure of the brightness of light multiplied by time) but the graph clearly demonstrates an increasing demand for light over two hundred years through the 1950s. Has the demand for lighting more or less saturated since then? Demand saturation is a pretty basic economic concept: there is a limit to how much an individual would want to consume of a good or service regardless of the price. For example, even if cookies are given away free at a banquet no one would eat a hundred of them, their demand would be saturated far before then.5)Unfortunately as it is also easy to see from this example we humans don’t seem to reach ‘saturation’ until well after what is Sustainable. Given delicious, low cost cookies, most people would probably eat several which would not be in their long-term health interest–the same applies to driving, flying, shopping etc. This phenomenon is what drives Jevons’ Paradox and is the focus of Conundrum.

Fouquet and Pearson found that lighting use began to sharply increase again in the 90s in the UK probably due to decreasing electricity prices and they and others have speculated that demand for lighting remains constrained by cost and that technological improvements or drops in electricity costs will lead to an increase in demand (as our friend David Owen worried about in Conundrum).6)Described in a recent paper by Fouquet and Pearson as well as more briefly in this blog post. I was unable to find similar data for the USA (the AEO reports only start in 2006), but a study from the Department of Energy in 1993 estimated that households used 940 Kwh of electricity for lighting which is significantly less than what was estimated in the first AEO report a decade later.7)Beginning in 1979 the Department of Energy has conducted Residential Energy Consumption Surveys every couple years, some of which report data specifically on electricity used for lighting. Unfortunately this does not appear to have been re-measured each year as they are just using the per-household level calculated by the 1993 study on lighting and multiplying that by the growing number of households. I believe that the 1993 survey probably under-estimated lighting use because they only counted bulbs on for more than 1 hour a day. But most importantly I was unable to figure a valid way to connect this earlier data with the AEO estimates for the last ten years. It was also estimated that the average American home had around 30 light bulbs while a 2010 study found the average had grown to 67.8)Again these numbers are probably not directly comparable because it does not appear that the study from the 90s counted bulbs used less than 1 hour per day while the recent one counted all bulbs. So I would tentatively conclude that consumption of lighting did increase in developed countries during the 90s.

Demand for Lighting is NOT Decreasing

We cannot conclude from this evidence whether those of us in developed countries have yet reached a saturation point when it comes to lighting. Some speculate that our saturation point won't be reached until indoor rooms are lit as well as the sun lights the African Savanna-in other words we have an evolutionary preference for certain light levels. Regardless of whether the demand for lumens will continue to grow in the developed world, we can at least say that it will probably not fall in any meaningful way. And given that most of the world's population is very light-poor we can speculate that global demand for light is set to dramatically increase-which typically would mean a vast increase in energy use and all its accompanying problems. But fortunately that is not the case, stay tuned for my next post to find out why:

Achieving Sustainability with Technology: the Exceptional Case of Lighting

The Series: Achieving Sustainability in Lighting

Aaron Redman is the founder of Achieving Sustainability and what passes for an administrator in these parts. Currently he is working on his Sustainability PhD at ASU while raising a baby daughter and taking advantage of nap time to foment discussions on this here blog.

Footnotes   [ + ]

1. The AEO’s most recent measured numbers are two years older than the report’s year, so this change is from 2004-2012
2. As with most trends, population/household growth should be taken out and the trend analyzed on a per capita basis, so I used the AEO’s data to do that and plotted the results here.
3. Well over a billion people in the world are still in this situation.
4. Fouquet, R. and Pearson, P. (2006) “Seven centuries of energy services: the price and use of lighting in the United Kingdom (1300-2000).” The Energy Journal 27(1) 139-77.
5. Unfortunately as it is also easy to see from this example we humans don’t seem to reach ‘saturation’ until well after what is Sustainable. Given delicious, low cost cookies, most people would probably eat several which would not be in their long-term health interest–the same applies to driving, flying, shopping etc. This phenomenon is what drives Jevons’ Paradox and is the focus of Conundrum.
6. Described in a recent paper by Fouquet and Pearson as well as more briefly in this blog post.
7. Beginning in 1979 the Department of Energy has conducted Residential Energy Consumption Surveys every couple years, some of which report data specifically on electricity used for lighting. Unfortunately this does not appear to have been re-measured each year as they are just using the per-household level calculated by the 1993 study on lighting and multiplying that by the growing number of households. I believe that the 1993 survey probably under-estimated lighting use because they only counted bulbs on for more than 1 hour a day. But most importantly I was unable to figure a valid way to connect this earlier data with the AEO estimates for the last ten years.
8. Again these numbers are probably not directly comparable because it does not appear that the study from the 90s counted bulbs used less than 1 hour per day while the recent one counted all bulbs.
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