We've just switched to LEDs in our kitchen / dining room / hall - a large open plan area with 12 halogen spots. These each had a 50W halogen bulb in when we first bought the property.
We've gradually moved to 35W, then B&Q "Eco halogens", which were 28W but with the light equivalent of 35W. These were excellent, with a great, really white light. The only problem was they lasted literally 5 minutes before blowing. I suspect they achieve the energy-saving by using thinner filaments.
Anyway, we've now moved to 5W LEDs - a big investment, but I'm hoping for a fairly quick payback. Trouble is, we have thick walls, small windows and are at the bottom of a hill. Plus, the sun doesn't get more than 8 degrees above the horizon in the depths of winter here. So we run the lights pretty much any time we're in the room, which is most of the time as it's where the stove is!
The LEDs are actually pretty good. Definitely not as "grey" as CFLs, instant-on and near-daylight in colour. Next step is to paint the walls with Dulux "Light and Space". This is apparently a great product and by no means a gimmick. Their advice to professional specifiers is that you can reduce window area by 25% and achieve same ambient light levels due to the higher reflectivity - but it looks like a matt finish. Again, expensive compared to regular paint, but getting light into the house is a major issue for us, so we're prepared to live with it.
Engage in geo-engineering. Plant a tree today.