How much megawatts U.S could save if they used LED for public illumination?
Bonus : The math for China which is another big energy consumer in the world. And the math for the humanity as whole.
Would like to know about % total energy saved too.
In one sense, a lot. But in terms of real life, not much. Lighting accounts for something like 6% of electrical use. (Please don't ask me to source that...) So if LED lighting cut that in half, it would only save 3%.
(Why half? LED isn't much more efficient than fluorescent lighting. Some LEDs would replace incandescents.)
The replacement cost is significant. Unless lighting is going to be used 24/7 probably the best strategy is to use LEDs when you ahve to replace lighting, but to leave existing lighting be until it breaks, or the building is being refitted.