A friend has actually been working on a more advanced implementation of the “cooler in the day, and warmer at night” idea – “designing a roof for hot climates that gets free cooling through radiant coupling with the sky…replac[ing] the standard insulation component with an open cell honeycomb… allow[ing] longwave radiation to pass, while arresting convection”.

Thanks to the fantastic way that most academic journals work, of course, I doubt you’ll actually be able to read the full text of that article…

Sparky: “Yup. Saving energy is good for the planet.”

Punter: “So, the more I use them, the more energy I save?”

Sparky: “Yup. And the more money you save too.”

Punter: “So, I should use them as much as possible, even leaving them on all the time?”

Sparky: “Yup… er, erm, well, no.”

Punter: “No? But if I don’t use them, I won’t save energy and help save the planet?”

Sparky: “Actually, I think you’re meant to use these energy saving bulbs as little as possible.”

Punter: “Oh, ok. I’ll not be buying any from you today then. Thank you. Goodbye.”

The problem is, these aren’t energy SAVING bulbs at all. They simply consume and waste less energy than incandescent bulbs. Any saving only occurs in the comparison or substitution, not intrinsically. The laws of thermodynamics prevent light bulbs from saving energy (even solar powered ones that simply store and release it).

They may well reduce the amount of energy mankind generates (from fossil & nuclear fuels) for its lighting, but that’s a reduction in generation, not an intrinsic saving of energy contained within the system known as planet Earth, i.e. storing it as fossil fuels, destroying it, or ejecting it into space.

The best way of saving energy (from heating up the planet), as opposed to reducing demand for its generation, on a domestic scale would be to mirror the surface of one’s roof and reflect a fraction of the sunlight’s energy that reaches it back into space. It thus keeps the house cooler in the day, and warmer at night. However, although it saves energy in operation it isn’t particularly economic (more energy may be consumed in its manufacture and installation than in its lifetime is radiated into space over and above an unmirrored roof), especially not for the householder (unless it saves on cooling costs).