September 2010: Chart of the Month

For reasons that don't bear explaining I have found myself looking into the latest government data on light bulbs. It was quite an illuminating exercise. For instance, I learned that we have cut our energy usage for lighting by 4% in the last 20 years, although on average the light bulbs we use are 43% more efficient. Hmmm, something up with that. The explanation must be that there are more of us, and we have more bulbs each. I chewed through the data and sure enough, the picture is as follows:

(Click on the image for a full size view)

To me, the column of interest in this chart is the third. It shows that we're each using more light bulbs, which is weird. But sure enough, that's exactly what we're doing. Think of a classic kitchen refurb: you take out a 100 watt centrally suspended bulb and replace it with 8 or 10 halogen spotlights, at 35 or 50 watts each. So the total energy requirement triples, at least. Sometimes it quintuples. There are now 170 million halogen lights in UK homes, more than the total number of energy saving light bulbs in the whole country.


Some people hope to solve this problem with LED lights, but I am not convinced. A 4 watt LED from Philips costs £22, compared to 99p for a 50W halogen spotlight . The LED lasts 20 times as long, and at 10p / KWh I estimate the cost of ownership is 6 times less per hour the bulb is used. But since the halogen spot only costs 0.5p per hour, and produces nearly 10 times more lumens  than the LED version, I'm not surprised if most people just can't be bothered with the calculation.


As usual, the source data is here for anyone who wants to check the maths. But more interesting than the raw data is the moral of the story: to make the kind of reductions in energy usage that we are currently targeting, we need the third column of this chart to start working for us, not against us. In this example, we need to stop ripping out low energy solutions and replacing them with high energy solutions. It just doesn't make sense. Perhaps we should introduce a tax (or a pox!) on halogen spots.