Friday, 13 December 2013

Replacing CFL bulbs with LEDs

I replaced the traditional incandescent bulbs in my flat some years ago and it was a no-brainer.  The compact florescent lights (CFLs) were coming rapidly down in price, were available in all the sizes I needed and of course consumed far less energy than the other heated filament bulbs they replaced.  I was happy to be saving energy and cutting my electricity bills.  All was good with the world, even though some of the bulbs took a while to "warm up" before they gave full output. I could live with that in most places.

Scroll forward to 2013 and I've now replaced a few of the first CFL bulbs with another new technology: mains power LED bulbs.  I need to replace some of the older CFLs that had failed over the 8 or 9 years I'd had them and Tesco (of all people) had new 4W LED bulbs on special offer at around £8 per bulb.  Now that's still a lot more than CFLs (which were being given away at one point and which you can quite happily get in pound shops these days).  However I wanted to try them out as I have four down lighters in the kitchen that are used quite a bit and where I could really do with the crisper, bluer, more immediate light from the LEDs.

I thus spent £32 on replacing 4 x 14W CFLs with 4 x 4W LEDs (compared to 4x100W reflectors that were there when I moved in over a decade ago!).  I liked the light and there's no "warming up" period (or at least none that I can detect).  Whilst the LED bulbs were more expensive the energy savings of having them on for a few hours per day on a regular basis means that I should be financially in front after 5 years or so, and the LED bulbs have a much longer predicted lifespan.

With that good experience under my belt, I started to wonder if there were other bulbs I should consider replacing in my flat.  The top contenders are the lounge standard lamp that is on for a few hours every evening, my bedside light (ditto) and the outside light above my front door (which could really do with a brighter light with no warm up whilst I'm trying to go up or down my iron staircase). As a result of discussions at the Footpaths Group at Loughborough University I started to wonder what the embodied energy of the various bulbs is and that's where things got alot more complicated.

Embodied energy is the energy required to actually make and distribute the product. The more complex the processing required to make a product and/or the more raw materials requiring high energy processing, the higher the embodied energy is.  The US Government funded an analysis of the embodied energy in different types of bulbs:

  • Incandescent bulbs require an average of 42MJ per 20 million lumen hours,
  • CFLs require an average of 170MJ per 20 million lumen hours,
  • Current LEDs require an average of 343MJ per 20 million lumen hours.
The "MJ per 20 million lumen hours" might seem to be a rather odd set of units, but it is basically used to standardise the amount of energy (MJ - mega-joules) over a fixed light output (the "per 20 million lumen hours") irrespective of the actual light output of the resulting bulbs.  This lets you compare the embodied energy required to replace, for example, a single very bright incandescent bulb with several CFLs or LEDs with lower light outputs (in lumens).

Now this looks bad for LEDs but the same report also shows the energy used actually lighting the bulbs. The traditional bulb consumes 15,100 MJ per 20 million lumen hours, the CFLs use up 3780 MJ per 20 million lumen hours and current LEDs sip just 3540 MJ per 20 million lumen hours.  This confirms that replacing traditional incandescent bulbs with either CFLs or LEDs is a good thing to do.  Even though both CFLs and LEDs have higher embodied energy, they consume about a fifth of the energy required to provide the standardised light output, and the energy used in lighting the incandescent bulbs dwarfs the embodied energy.

The tricky call is replacing CFLs with current LEDs though.  Whilst the energy used in powering the LEDs is 240MJ less per 20 million lumen hours, they require 173MJ more to make.  So they do win out in the end energy wise but the break even point comes rather late in their life.

I'm probably still going to replace my high use CFLs with LEDs.  However waiting a while may help: mains powered LEDs are still a relatively young technology and the energy use, embodied energy and prices are all likely to fall over the next few years.  My existing CFLs are still pretty good, so its probably best to wait until they break, and then make the switch to LEDs.