That holds about as much water as a Sainsbury's trolley, is typical of people selling lights and not taking account of consumers wishes and needs and lifestyle. I don't want 10 lights each with different brightness, nor can I afford the cost of purchasing them, getting them wired and servicing them with over rated and massively expensive cfls. cfls damage the environment, give poor quality of light, create migranes in those susceptable and do not last as long as they are claimed making them poor value for money.It's the old story — pay more at the outset and reap the rewards in running costs. As has been mentioned earlier, the efficient way to alter the lighting is to have a number of lights in the room and to switch them on as appropriate. They can all be low energy lamps then. In addition, you can alter the location of the burning lights to suit mood.
As an engineer the solution you suggest is the worst of all worlds. The best engineering solution is simplicty - one light with variable brightness - oh that sounds like a dimmer. What we need to solve is the efficiency of dimmers and lights which are safe, cheap and produce quality light.
In the mean tiime, I'll stick with incandescent or halogen and dimmers where necessary