One disturbing aspect to be taken into consideration when measuring effects of energy efficiency campaigns is the rebound effect.

That is as energy efficiency of some process is improved, the same process gets cheaper and that provides incentives to its increase of use. The total consumption of energy changes less than proportionally to changes in physical energy efficiency. The rebound effect is quantified as the extent of the deviation from the proportionality. [1]

This would mean for example, people would consider having two efficient cars in their households instead of one. Another phenomenon for example is the increase in garden lightings with the introduction of efficient bulbs.

It has been suggested that ironically, the amount of waste is insensitive to improvements in efficiency.

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Wikipedia The Rebound Effect

[1] Kenneth A S, Kurt Van Dender (2007), “Fuel Efficiency and Motor Vehicle Travel: The Declining Rebound Effect”, The Energy Journal 28 (1)