Further challenges in store for energy

Your special issue on "energy challenges for the 21st century" (July pp13–15 and pp25–45) was informative and interesting, but failed to mention the overall energy or environmental budget. None of the articles compared the energy used in the manufacture of a conventional car or light bulb with that of their "energy-saving" replacements. This is, of course, a complex matter, especially if one considers the energy used in maintenance. A new type of traffic light, for example, might require less energy to run, but might also be more reliable, last longer and require fewer visits from repair crews.