How are you going to measure it, by Watts, Lumins, Expected Life and are you comparing it just to incandescences or to LEDs too or just over a fixed time period?
I bought some 8 and 12 W CFL last year for 10p each, they are now £1.80 to £2.40.

Having just run a test with a small CFL that is rated at 8W but takes 9 to 10 with a power factor of 0.4. Does that mean it is really using (as in paying for) an extra 5 to 6 W?

Seems to use 0.01kWh per hour or in real terms 10 W for an 8 W. 20% tolerance, seems usual for the electrical/electronic industry.

Posted By: SteamyTea: “Having just run a test with a small CFL that is rated at 8W but takes 9 to 10 with a power factor of 0.4. Does that mean it is really using (as in paying for) an extra 5 to 6 W?”

No. As a normal domestic electricity consumer if you use 9 W of real power then you pay for 9 W, within the limits of meter accuracy, even if your power factor is 0.4. A larger industrial user might well pay for 9/0.4 = 22.5 VA, though.

I replaced all of my bayonet fitting 60-100W incandescent bulbs last year when Homebase were offering 8-11W CFLs for 10p. The light output isn't of the same quality, but they turn on quickly & its good enough for most purposes.

Assuming you're replacing a 50p 60W incandescent bulbs with a £3 8W CFL, the electricity costs 12p per kWh & you consider the light output equivalent then its paid for itself after 400 hours of operation. In other words, you save £2.50 in electricity charges after 400 hours of operation.

However, that's not the whole story because it will continue to save you money after the break even point and CFLs are supposed to have a longer life than incandescents. So it could save many times its purchase price in its lifetime.

David

I work on a 1:4 replacement ratio - i.e to properly replace a 60W bulb you need a 15w cfl.

In my kitchen, for example, which is a bit gloomy, I reckon the light is on 2000 hrs/yr (8000 hrs in a year, roughly). I replaced a 100W bulb with a 25w cfl. So I'm saving 2000 x 75 watt hours per year = 150kWh. So thats about 150 x .12 pounds (£) per year = £18 per year. cfls cost about £2 - £3 (prices may vary) So any space where the light is on more than a few hundred hours per year will pay for itself within a year.

Tim

Our Megaman GX 53 CFL's have not done well - half failed after 12-18 months so payback is not good. Anybody had any experience with these?

WE have just moved into a "new" house. In the kitchen there are nine 35W halogen bulbs (GU10s). These cost £2.5 - £4 each and have a life of 1000 - 4000 hours. Two have failed within 5 months though their actual age is unknown. I have replaced them all with Philips LED GU10s (£10) with a quoted life of 25,000 hours and an energy consumption of 4W.
Looking at the cost of the bulbs over its life, Halogen £3/2000 Hrs ~ .15P/Hr, cost of LED bulb £10/25000 ~ .004 P/Hr. One year ~ 8000 Hrs, so if the bulb is on for 30% of the time (2600 Hrs) cost of electricity for Halogens = 2600 X 35 x 12p X 1/1000 = £10.9,for LEDs = 2600 X 4 X 12p X 1/1000 = £1.20. Working out the cost of bulb replacement, Halogens, 2600 X .15 = £3.9, for LEDs, 2600 X .004 = £1.04. So for one halogen at 35 Watts, it'll cost me £14.8 or for the LED equivalent, it's £2.24, so I save about £12.5 on every bulb I change in the kitchen - times 9 is £110 per year.
And there are more savings!, its a bungalow so each bulb has a "box" around it to stop the loft insulation covering the lamp holder and causing it to over heat. So when the lights are off, I have nine 6" square holes in my loft insulation, these will be attended to when the weather improves.
Frank

In my bedroom lots, in my lodgers, none

Not going to mention the light tonight, already mentioned the 20+ minute shower, we are both sulking now.

ST - I think the term is incentivisation
Or just fit one of those shower taps that you keep on having to push to keep the water flowing - swimming pool type showers, the name for which eludes me at the moment. Or a timer that takes 50p pieces

Posted By: TerryOur Megaman GX 53 CFL's have not done well - half failed after 12-18 months so payback is not good. Anybody had any experience with these?

not had much trouble with GX53s, but have had problems with GU10 cfl dimmerble from megaman , 50% blow rate in 3 years on one project , wont use them again , I presume the dimming function just to much for them. Waiting for the LED dimmaerables to drop in price, which will hopefully be a longterm replacement for GU10 halogens that everyones gone crazy for over the last decade or so .

As to payback , CFLs in standard fittings payback within a year , triphosphor tubes again very quick payback , the more expensive LED and CFL designs , well time will tell depending on how long they last. Not had any LED blow yet , other than a few faulty within a couple of days and some GU10 LED in downlights failing after the first few months ,down to over heating in units ,found out later instructions did state they weren't suit for downlight use.

I have got over a 100 low energy light bulbs that cost less than 8p each sitting in my cupboard so the question is will I get through them before a newer better design comes along.

I did work out sometime ago that it was best to replace 60w older style light bulbs straight away rather than before they blew, but I was down a pub so no real evidence.