It is indeed. But that looks more like a reference to the supposed % energy saving claimed, not a suggested heat replacement factor.

However if it is a back of an envelope calculation you could always show us your workings.

you double accounted for the 80% !!

There is also a swing towards winter as lights on longer and heating needed more 5:1

reduced by some low energy bulbs used outside 5% would be an over statement.

I would much rather that the calculations ware all done in energy terms.

Double accounted? What do you mean?

Steamy -- I dont like percentage savings especially of carbon because where is or was the starting point etc and then it is too easy to fudge the width of the goal posts.

I've not double counted anything Tony, just trying to make sense of your somewhat confusing statements. I'll go through an example again and explain the arithmetic (leaving aside carbon and cost).

100w bulb on for 1,000 hrs equates to an energy use of 100kWh.

Replace that with a 20w bulb for 1,000 hrs and the energy use is 20kWh.

On the face of it that's a saving of 80kWh (or 80%).

However it's not that simple because of the Heat Replacement Effect. Earlier you referred to a "figure for heat replacement compared to the 80% I am suggesting". A HRE of 80% would mean no energy saving at all, that 80kWh of replacement heating would be required to make up for the 80kWh less of lighting. For that to be true, for the typical household, lights would only ever be used when there was heating on. So in effect there would have to be no such thing as summer.

Is that what you're suggesting Tony? That there's no such thing as summer? If so, good luck with that.

Because if any lights are used when the heating isn't on, the HRE has to be less than 80%, at least in the typical household. Because an 80% factor isn't credible, I looked again at the other statement of yours you pointed to in your first post.

"In this way 80% of the savings being claimed are not being made in the real world."

80% of the savings aren't being made, eh? That would mean 20% are.

And with our hypothetical 100w bulb what were the original savings 'claimed'? 80kWh.

And what's 20% of 80kWh? Why that would be a 16Kwh saving on the original 100kWh.

That means energy use would be 84Kwh, consisting of 20kWh of low energy lighting and 64kWh of replacement heating.

Or in other words a HRE of 64%.

I only use 80% of 80% because that's what you suggested in your first post.

But this 80% of 80% is just a figure you've plucked out of thin air.

The actual figure, based on research, is much lower and suggests a heat replacement factor of 21%, or alternatively a saving of 59% on the useful energy of the lighting.

In any event the motivating factor for switching to low energy bulbs isn't really a reduction in energy use. The principal factors are cost & carbon and in those terms, for the typical house, the % savings are much higher than the energy savings.

Why?

I've already given rough figures which suggest that, for a typical house and compared to a standard bulb, a low energy bulb will result in an energy saving of about 59%, a CO2 saving about 72%, and a cost saving about 73%.

The 80% saving usually quoted is an oversimplification but it is at least, albeit in a narrow sense, true. Any other way of expressing the saving starts getting complicated and the average % cost & CO2 savings aren't far off anyway.

Your engagement with the laws of physics seems very selective, and taking your ball home when no one is agreeing with you doesn't really seem terribly reasonable either.

I see entirely why you find it counter-intuitive, but that doesn't necessarily make it wrong.

Rgds

Damon