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Sat Apr 22, 2017, 01:56 PM

Earth (NASA)

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Reply Earth (NASA) (Original post)
demmiblue Apr 2017 OP
hunter Apr 2017 #1

Response to demmiblue (Original post)

Sat Apr 22, 2017, 03:19 PM

1. I think it's fascinating how cities that once glowed yellow-orange now glow white...

... as sodium vapor streetlights are replaced by LED streetlights.

The guys who invented the blue LED (and won a Noble Prize for it), which is the basis of white LEDs, have changed the nighttime world as seen from space.

When I was a kid the lights on our street used big 300 watt incandescent bulbs that required huge amounts of energy and had to be replaced frequently. Replacing streetlights was a full time job for some people. Those lights were replaced by more efficient and longer lasting mercury vapor lamps which cast an eerie bluish light that made everyone look like zombies. Those were then replaced by high pressure sodium lamps which didn't seem as awful.

Now our city has replaced all the sodium vapor lamps with more efficient LEDs. Sometimes I'm a little nostalgic for the orange streetlights because that's the light our kids grew up with. Maybe I associate the LED streetlights with them moving away from home.

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