Traditional incandescent lights have terrible efficiency 2.5% or so. The benefit from Old Incandescent vs LED's is huge (5x to 10+x), but there is just not much room from the best LED's to 100% efficiency making the remaining gains less important. https://en.wikipedia.org/wiki/Luminous_efficacy
PS: Power is kind of an odd thing. Direct costs are so cheap most people ignore it, but the external costs are high enough to push efficiency gains. Taxes would be the best solution, but politics is odd.
There you go. Set the "sales" tax rate on a luminous efficacy sliding scale. The lower the efficacy, the higher the tax %. It'd have to be some kind of wholesale/manufacturer tax, at least in the U.S., so that it's reflected in the sticker price before checkout.
EX: 303lm/w vs maximum possible 683 lumens/w. http://www.cree.com/News-and-Events/Cree-News/Press-Releases...
PS: Power is kind of an odd thing. Direct costs are so cheap most people ignore it, but the external costs are high enough to push efficiency gains. Taxes would be the best solution, but politics is odd.