Just bought and installed my first set of GU10 LED downlighters. I went for Philips 'PerfectFit' 6W 3000k 40degree ones, and replaced a bank of 4 x 50w halogen downlighters.

These things are incredibly white and bright. I'd expected the 3000k ones to be a bit yellower than the halogens, which I'd read are 3100k, but they are actually much whiter, so I can't imagine what the 4000k ones must look like, some kind of dazzling blue-white I guess. Perhaps its the quality of the light, but the LEDs seem brighter, and really bounce light off the white Corian worktop in our kitchen, and seem to give much crisper shadows, probably because the light comes from a single small source.

Dimming with C-Bus2 1A dimmer is very similar to the halogens, I left a halogen in one fitting to compare them, and the LED dims down to almost exactly the same point as the halogen before it goes off, but remains white rather than going very yellow as the halogen does. No problem using 4 on a circuit, no dim light showing when they are switched off, which had been a worry.

I 'd thought I'd just replace one bank of halogens, and use up the displaced halogen bulbs as in the other bank as needed, but I love the quality of the light they give off, so have ordered a set for the other bank.

They are expensive, don't know if the business case really stacks up, but with a bit of 'man maths', these things are a good buy, I paid about 15 each with postage from ebay. No doubt they will be 5 in a couple of years, but having tried them, I had to buy more. Now, about the ones in the hall ....