There has been a very rapid rise in the use of low energy lighting luminaries in the last few years. At first sight it would appear that as a consequence large amounts of energy are being saved. However if we look a little more closely we quickly realise that that this might not be the case.
In a heated building at a particular point in time the amount of energy required to keep a room at its design temperature is fixed. For the sake of argument let us say that the room in question needs 500W to keep it warm. This energy is supplied by a radiator that emits 400W and a 100W light bulb. Now someone fits a low energy light bulb which only needs to use 20W to light the room to the same level as the old incandescent one did. The problem now is that the room has only got 420W of energy going into it but its heat loss is 500W so it will be colder. In order for us to maintain the temperature at the same level as before we must now supply 480W through the radiator. Thus no energy has been saved.

400W + 100W = 480W + 20W

The uptake and increase in the use of low energy light bulbs is being used by central government as way of meeting our carbon reduction targets YET NO ENERGY IS BEING SAVED!
Many reports on energy use in buildings are assuming quite incorrectly that energy and costs are being saved in the winter, whereas, no energy is being saved although some costs might be depending on the relative costs of the different energy sources used. In the summer there will be a cost saving but lighting is used less as it is lighter for later into the evening and light early in the mornings. In this way 80% of the savings being claimed are not being made in the real world.

I call this over-accounting.

What about lighting in the summer when we don't need to heat our homes (if the insulation and thermal capacity are balanced). No need then for that lighting heat?

Tony, I am with you mate, I have used this argument many times and untill a decent low energy lamp at a decent price is sold I am not changing "some" of mine, however I dont mind using CLF's in places that require lamps on for a long time and you dont mind the bad quality of the light. I think LED's will come on a long way and eventualy give us a good replacement.

Posted By: DamonHDTony: you keep raising this old canard as if repeating it will change the laws of thermodynamics.

Sing along now

The First Law of Thermodymamics:
Heat is work and work is heat
Very good!

The Second Law of Thermodymamics:
Heat cannot of itself pass from one body to a hotter body
Heat won't pass from a cooler to a hotter
You can try it if you like but you far better notter
'Cos the cold in the cooler with get hotter as a ruler
'Cos the hotter body's heat will pass to the cooler

First Law:
Heat is work and work is heat and work is heat and heat is work
Heat will pass by conduction
Heat will pass by convection
Heat will pass by radiation
And that's a physical law
Heat is work and work's a curse
And all the heat in the Universe
Is gonna cooool down 'cos it can't increase
Then there'll be no more work and there'll be perfect peace
Really?
Yeah - that's entropy, man!

And all because of the Second Law of Thermodynamics, which lays down:
That you can't pass heat from the cooler to the hotter
Try it if you like but you far better notter
'Cos the cold in the cooler will get hotter as a ruler
'Cos the hotter body's heat will pass to the cooler
Oh, you can't pass heat from the cooler to the hotter
You can try it if you like but you'll only look a fooler
'Cos the cold in the cooler will get hotter as a ruler
That's a physical Law!

Oh, I'm hot!
Hot? That's because you've been working!

Oh, Beatles - nothing!
That's the First and Second Laws of Thermodynamics!"

Incandescent lights have a colour temperature of 2700k to 3300k.

There are numerous bulbs available in this colour temperature often termed warm white or soft white but always check the colour temperature.

try a philips softone about £7 each.

Nigel -- I like you answer the best

you said, "So whilst you are correct in terms of energy you are not correct in terms of carbon emissions."

so in energy terms you agree yet you say in environmental terms it is all good :-

400W of gas = 88 g of carbon plus 100W electricity = 41g >> 129g of carbon

480W of gas = 105.6g plus 20W electricity = 8.2g >> 113.8g of carbon

difference is 12% yet HMG is claiming 100% of the 80W saved and this is what winds me up as it is untrue.


Not all the energy that is being saved by using low energy light bulbs is being saved nor is all the carbon only a proportion of it is

Yet this 100% is being used to meet our carbon targets -- OVER- ACCOUNTING in my book

Tony - you keep raising this exact same point.

When we loose the will to keep pointing out what you are saying is only partly correct that won't make it undesputed fact...

OK then guys so are you saying to me that HMG is correct to claim that all of the 80W saved by using low energy bulbs can be multiplied by the number sold and their average use and then that figure turned int carbon saved and deducted from the target set?

I do not agree and this is why I am on the case of over-accounting.

Nigel,

Thanks for the recommendation, have looked at the argos website and indeed a bargain at £3.99 but I notice that quite a few people give the bulbs a poor rating for longer than standard CFL startup time and some say not bright enough. I will however buy some and give them a go.

A lot of the carbon calculators and figures for estimated savings (financial and CO2) do take the heat replacement effect into account.

seanie -- show me these please

And I've come across it elsewhere. It's a well known factor even if there's uncertainty about the extent of the effect.

Posted By: nigelIncandescent lights have a colour temperature of 2700k to 3300k.

There are numerous bulbs available in this colour temperature often termed warm white or soft white but always check the colour temperature.

What I don't quite understand is this table...
http://www.efi.org/factoids/cri.html
It says warm white CFL have a worse CRI than cool white. Yet many people seem to prefer warm white?

The philips softone has a CRI around 80 I think.

Sounds like over-accounting to me still

21% sounds like a very low figure for heat replacement compared to the 80% I am suggesting