1) The source is this paper from Denmark by Gydesen and Maiman.
http://www.iaeel.org/iaeel/Archive/Right_Light_Proceedings/Abstracts/RL1_Abstracts/RL1AbE11.html

2) 8000 hours is the typical quoted lifespan, with some manufacturers claiming more. It’s the figure used in the Danish paper. It’s worth noting that performance does tend to drop off over time with CFLs so they may be replaced before they actually fail. The difference is so large that the return on investment will still be high.

On your other points, the figures don’t exclude disposal. The 1/9 x embodied energy includes the end of life cost. It’s also worth noting that CFLs release about half the amount of mercury to the environment per hour of use as incandescent bulbs, due to the reduced mercury from coal-fired power stations.

On recycling, CFLs are technically covered by the WEEE (waste electrical and electronic equipment) directive meaning that the retailer is obliged to take them back once they fail. Apparently only IKEA actually have a scheme in place for this. CFLs can also be recycled in the WEEE section of local recycling centres. Incandescent bulbs are not covered by the directive.

And finally, you’re absolutely right. The best option is to maximise daylight through light room surfaces, larger windows, daylight sensitive lighting control for offices, etc. There may be an energy penalty from the larger windows (depending on orientation, U value, etc – let’s leave that one for another day!) but the other two are virtually free in terms of embodied energy.

I’m glad you found the post interesting and I hope this clears up some of your questions.

1) What is the source of the embiduied energy for CFL being 9 times that of conventional bulbs – I do not dispute it but I would like to know the source.

2) In terms of these bulbs lasting 8,000 hours, again I wonder where this is from (most likely the manufacturers.)

The key point here, taking your point that lamps are only used 3.5 hours a day, this equates to over 6 years of use – I suspect most lamp fittings get changed (certainly domestically) in this time period when the room is redecorated.

The “ven” diagrams are good but they are missing a valuable point, disposal !! CFLs contain more chemicals (inlcuding as you point out mercury) thus they will have a bigger impact on the environent when disposed. If people were charged for disposing of them (in relation to the real disposal costs) – I suspect they would think twice about buying them.

The fact is, the savings are longer term, not “instant” as the promotion makes ot. the best solution is not to use the lamp in the first place i.e. make sure wherever possible, that natural light is utilised – a factor that is not always taken into account when designing buildings.

I’m assuming this won’t work for Mac Office though… (

So no, no error. But please do bear in mind that with so few data points, and with assumptions having been made, these numbers are only approximations.