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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.

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    Should answers also consider cost of replacing and what will be done with old setups? Bare energy consumption comparaison would still be interesting by itself but might be considered as 'incomplete' from some points of view. – JeromeJ Sep 7 '15 at 21:08
  • Well if you can sure, do you mean the ecological cost or the economical cost ? If economy I don't think there much reason to care...is already known that is cheaper in the long run when compared to low efficiency and low life time lamp's.... You could assume that the old setups will be all recycled, many countries already have high recycling rates so it's make sense they would be recycled – Freedo Sep 7 '15 at 21:52
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    In relative numbers not that much. To give you an estimate, I know that in the Netherlands approx 2% of total electricity generated is for lightning. And electricity generation is only 20-25% of our total energy consumption. That would make it approx 0.5% But in absolute numbers this could mean a few power plants less. – Jan Doggen Sep 8 '15 at 9:45
  • I guess that every % counts if we want to fight global warming. I guess in the future cities will change everything they can to more efficient tech – Freedo Sep 9 '15 at 2:17
  • The answer to this for public lighting is much less straightforward than for domestic lighting, because most of it was not using incandescent lighting to start with. The benefits of LEDs compared to discharge lighting exist, but are more nuanced and less clear cut. Eg in strict efficacy terms, street lighting has produced fewer lumens per watt since moving away from the mid-20th century low pressure sodium lamps. I'm not going to attempt a quantitative answer, but if you were to change the question to a more exploratory one (eg "would the US save...") I'd have a go out outlining the issues. – Flyto Sep 10 '15 at 9:57
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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.

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