Reality Check: ‘Lighting accounts for 20 per cent of electricity use’

How much electrical energy do we use for lighting? The figure widely quoted is 20 per cent of the total. By moving to more efficient technologies we can, apparently, reduce this to 10 per cent. It’s hard to say where this 20 per cent figure comes from originally, what it’s based on or how accurate it is. I can trace it as far back as an early Lumileds presentation from 1998.

The figures for different countries in Europe are interesting in the light of the current economic troubles. Greek households are among the biggest users of energy for lighting both in percentage terms of total electricity consumption (18 per cent) and in absolute terms (1,012kWh a year). Compare this with Germany, where the figures are eight per cent and just 310 kWh per year.

 ‘You can save up to 30 per cent by dimming to 50 per cent of the 40 per cent of the 20 per cent of electricity used for lighting’

 It’s hard to say where this 20 per cent figure comes from originally, what it’s based on or how accurate it is. I can trace it as far back as an early Lumileds presentation from 1998.

So while Fritz and Helga are out working hard, Costas and Eleni are sat in front of the TV with all the lights blazing. The sad thing for the German consumer is that they are paying nearly as much money, because energy prices in Germany are twice what they are in Greece. It looks as though it’s the higher energy prices in Germany that have led consumers to adopt more efficient technologies sooner than their Greek cousins.

In the residential sector, where stories of EU bulb bans and toxic CFLs make for great headlines, another report suggests that the sector accounts for only 10 per cent of the electricity used for lighting, which means two per cent of the total electricity used, if the percentage used for lighting is 20 per cent. The same report suggests that about four times as much is used in offices (eight per cent of all the electricity used).

But these numbers are of little practical use, except that they tell us that in a large building full of computers and lights, a significant chunk of cash is burned keeping it lit, and another chunk probably goes towards getting rid of the waste heat from the lights (unless it’s winter of course). I’d hazard a guess that if you invest in the most efficient lighting, air conditioning and computer equipment, then the percentage probably remains the same.

Unfortunately percentages have been creeping into lighting manufacturers’ datasheets and presentations. For office lighting you can fit a control system that can save up to 30 per cent, by dimming to 50 per cent of the 40 per cent of the 20 per cent of electricity used for lighting, and combine this with the LED product which offers to save 50 per cent of the 40 per cent of the 20 per cent of electricity used for lighting. And why not add in a bit of daylight and save another 30 per cent? Don’t forget that the space may have been overlit by 20 per cent in the first place. Confused?

Percentages are fantastic tools to dress up quite complex scenarios, very useful for politicians and high-level discussions about macroeconomic factors, but not much help when you’re trying to delve into detailed applications and work out if it’s worth bothering undertaking a lighting-based energy-efficiency project.

Thrashing out a value proposition can be real grunt work: you have to establish the cost of light in the first instance, with variable operating hours, complex electricity tariffs and lamp wattages that don’t match circuit wattage, and then throw in the latest lighting recommendations and a sprinkling of emergency lighting to the mix. It’s not always the ‘low-hanging fruit’ politicians make it out to be.

To save yourself time, refer to The Hitchhiker’s Guide to the Galaxy, which reveals that the answer to the Ultimate Question of Life, the Universe, and Everything is 42. And funnily enough, if you take 42 per cent of the domestic lighting electricity use in Greece you get pretty close to the figure for Germany.

So there we have it: the answer is 42. Now, what was the question?

 

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