The ROI isn't there - and won't be for years. The big advantage of LEDs, economically, is in increased lifetime, and the reduced labor costs associated with replacement - which is why LEDs appear in stoplights, airplane interiors (new 787). The other big advantage is a smaller package size - why they are making big inroads in automobiles, taillamps currently, with HBLEDs appearing in headlamps in the next few years. Oh, and making them uses a bunch of really nasty chemicals like Gallium and Arsenide.