It appears that MIT scientists are making it happen on a picowatt scale. Of course if they catch up with Tesla who was doing it on a megawatt scale progress will be at hand. Simply put if electrons are moving and a braking force is applied you convert electron inertia into energy. If the ligt is then converted into providing the braking force we should have enough energy until every single electron on Earth isn't moving which will be a long long time from now.
http://inhabitat.com/mit-researchers-create-led-light-that-exceeds-100-percent-efficiency/led-light-2/ (http://inhabitat.com/mit-researchers-create-led-light-that-exceeds-100-percent-efficiency/led-light-2/)