Effect of daylight saving time on lighting energy use: A literature review
Introduction
Lighting has a profound effect on the lives of humans. It facilitates vision, which is our most important source of information on the world, and it affects our basic biological functioning through its effect on our ‘body clocks’ (Webb, 2006); access to daylight and sunlight affects the form of our buildings and our cities, and provision of electric lighting is one of the world's biggest end uses of electricity. For industrialized countries, national electricity use for lighting ranges from 5% to 15% of total electrical energy use (Mills and Orlando, 2002). Because this energy is often supplied by fossil-fuel generation, provision of lighting results in the large-scale release of greenhouse gases (GHGs): 1775 Mt of carbon-dioxide emissions, according to a 2002 estimate (Mills and Orlando, 2002). Further, lighting is a major contributor to the peak demand for electrical power, which is often met by expensive, high-GHG generators.
Because of its high-energy burden, lighting has often been the target of energy efficiency initiatives. One such initiative is daylight saving time (DST). The principal reason for the introduction of DST was to shift human activity patterns to make better use of daylight, and thus reduce the amount of electric lighting necessary to support these activities. There are several other effects of DST, including changes to traffic fatalities, and commercial activities.
Beginning in 2007, DST—or summer time in Europe1—was extended by 1 month in the US and Canada (with some exceptions). DST started on the second Sunday in March and will end on the first Sunday in November. The new begin and end dates are set in the 2005 US Energy Policy Act (Energy Policy Act, 2005). To investigate the influence of the extension, the Act included the commitment that “not later than nine months after the effective date of the 2007 DST, the Secretary will report to the US Congress on the impact of the extension on energy use in the US”. Depending on the results, the Congress retains the right to revert DST back to the 2005 time schedules. Canada followed the US in extending DST; this decision may have been more about avoiding chaos in financial and commercial areas due to lack of clock synchronization, than about expectations of energy savings (Beauregard-Tellier, 2005). In Europe, agreements are signed until 2007 (Fontaine and Ringholm, 2001). The European Commission will submit a report in 2007 with suitable proposals for continuation or change (Fontaine and Ringholm, 2001; De Bruijn and Van Poppel, 2005; EurLex, 2000).
North America and Europe are not the only areas in the world to observe DST. For example, on the African continent, Egypt, Tunisia, and Namibia have DST. Israel, Palestine, and Jordan observe DST, and both Australia and New Zealand introduced DST to save energy. Mexico has observed DST since 1996, and Cuba, Honduras, and Guatemala introduced DST in 2006.
The purpose of this paper is to review the literature concerning the effects of DST on energy use, particularly with regard to lighting, and to derive implications for energy policy. First, a short overview of the historical background of DST is given. Second, we give some simplified estimates of effect size, with a focus on residential lighting. Third, research conducted between 1968 and 2007 is discussed (mainly in chronological order). This research was conducted to better estimate likely effects, or to demonstrate effects from measured energy use data. We also briefly describe some of the research into the non-energy effects of DST. Finally, a general discussion with regard to the available knowledge, better effect estimates, and design possibilities is presented.
Section snippets
Historical background
In 1784, Benjamin Franklin, the American Minister to France, wrote a letter to the editors of the Journal of Paris about “the waste of both candlelight and daylight”. Franklin was not proposing DST, but rather suggested that people get up and go to bed earlier, thus saving money on the purchase of candles (Franklin, 1784).
In 1907, the Briton William Willett published a pamphlet entitled “The Waste of Daylight”. In this document he proposed advancing clocks by 80 min in the summer. On successive
Simple estimate of potential lighting energy savings
The potential of DST to save energy rests primarily on projected effects on residential lighting use. The assumption is that with more daylight in the evening, residents will delay switching on electric lighting in their home. Advancing the clocks 1 h implies that lights will be switched on an hour later in the evening. Assuming the bedtime of residents does not change, this suggests that the “on time” of lighting with DST will be 1 h less than without DST. Combining this basic assumption with
Research on DST (1968–2007)
In 1968, the UK began a 3-year trial of so-called British Standard Time (BST), which was implemented year round (YRDST). The clocks were advanced 1 h in March 1968 and not put back until October 1971. A review of this trial by Her Majesty's Stationery Office (HMSO) (1970) concluded that it was impossible to quantify important advantages and disadvantages and drew no conclusions either in favour or against YRDST. Demand for electricity increased by 2.5% in the morning peak period, but reduced by
Non-energy effects of DST
The primary reason for the introduction of DST was, and still is, to save energy. Nevertheless, the 1-h clock change influences more than energy use alone. Therefore, some authors have discussed other DST effects in their reports. DST may affect traffic safety, business, and leisure time, and may have physiological and psychological effects.
Shapiro et al. (1990) indicated that neither the change in photoperiod nor the effect of a small change in circadian rhythm, both associated with DST, had
General discussion
Studies have demonstrated effects of DST on traffic, health, leisure, and safety. However, the principal reason for introducing and extending DST was projected energy savings, particularly for electric lighting. Support for this in the research is mixed. Several studies claim to have demonstrated the expected reductions in overall electricity use (∼0.5–2%), largely as a result of residential lighting reduction. However, there are just as many studies that suggest no effect, or that the data are
Conclusions and suggestions for future research
Based on the literature review, conclusions about the effect of daylight saving time (DST) on (lighting) energy use are as follows:
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The existing knowledge about how DST affects energy use is limited, incomplete, or contradictory. Many conclusions are the result of expectations alone, are based on constrained assumptions, or are older than 25 years.
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Economical, geographical, and climatological factors have major effects on electricity end use. Studies should always correct for such factors.
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Energy
Acknowledgement
The authors are particularly grateful to our colleague Dr. Christoph Reinhart for some of the initial ideas for this paper, and for his review of the text.
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