GU10 CFLs (aka energy saving spots)

I decided it was time to fit low-energy bulbs in our kitchen/diner. We currently have 2 surface mounted fittings, a 4-spot bar fitting in the kitchen area and a circular 3-spot in the diner area. There are signs that the 4-spot was a replacement for a traditional florescent tube whilst the 3-spot probably replaced a simple pendant lamp.

When we moved in, the 4-spot contained 4 50w halogens and the 3-spot contained 3 50w halogens. So 350w total power consumption to light the room. Shortly after we moved in, two of the bulbs in the 3-spot blew. One was replaced by a 9w Megaman CFL, the other was left in place, not working. (So total power consumption reduced to 259w).

Since we got the currentcost and it was easy to see how much the 4-bar was using, we've mainly used the 3-spot, just using the 200w 4-spot when cooking. But now with the twins, we're at home a lot more and using the kitchen lights more. Another halogen has gone so I've decided to get a full set of CFLs.

But whilst "traditional" bulbs were normally quite a simple purchase (select shape, select wattage, done), CFLs add colour temperature to the equation. And this isn't always obvious.

Cool white vs Warm white vs "real" light
First off, there seems to be no set standard for the use of the terms "Cool" and "Warm". The real comparison should be made using the colour temperature measure.

The measure is between how 'white' a light looks vs how 'yellow' it looks. The higher the number, the closer it will look to outdoor daylight. The lower the number, the more 'yellow' it will look - but as traditional light bulbs are quite 'yellow', we are often pre-disposed to expecting artificial lights to be like this, so we often prefer the more 'yellow' (lower temperature) bulb. At least this is how it seems.

Another reason the "warm" and "cool" terms seem counter-intuitive is because our experience of heat temperatures means we expect "cool" to be a lower number than "warm" - as it is when we heat a room, for instance. However it is the opposite for colour temperatures - "cool" has a higher value than "warm".

To put this in a simple comparison:
real daylight : most likely >6000k
so-called "cool white" : ~4000k
so-called "warm white" : ~2700 - 3000k
traditional halogens : ~2500k

Changing the kitchen to CFLs
In the end, I decided to stick to the Megaman 9w 3000k to match the existing, as the light output seems adequate (albeit based on testing with just 1 bulb). Changing the remaining 5 (+1 already dead) bulb to these CFLs will drop the full power consumption from 259w to 63w. That's 159w less.

As at Feb '09, TLC Direct seems to be giving the best price (excluding ebay) at £7.25 ea including VAT.

So we save the planet but does it save money?
This is the part I am most sceptical about.

With our current "high" usage of the kitchen (I estimate 8hrs per day for the diner part, 2hrs per day for the kitchen part), a conservative estimate during the winter half of the year is ~10p / day reduction in electricity or ~70p/week, approximately £18 / year. With the CFLs costing approximately £40, that's a payback of around 2 years.

... Watch this space for updates when we've fitted them all.