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Is light pollution less bad later at night?

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#1 RobH2020

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Posted 15 January 2020 - 04:59 AM

I've tried searching the forums and Google for this, not sure it's got much coverage.

 

Does anyone find that light pollution diminishes as the night wears on? As the general population goes to bed, turns off house lights, cars stop being driven, shops and factories shut down... 

 

In my area, they even turn off most of the street lights on quiet residential streets after midnight.

 

However, I'm 30 mins train ride from the centre of London - this is lit up so brightly at all times that when I lived there and got used to the brightness I was actually confused about the darkness at night when I visited my parents at Christmas. It was so unfamiliar to walk around in the dark! 

So anyway I'm not sure if the proximity of London means that local lights being turned off have little effect.

 

What's anyone else's experience?



#2 Tony Flanders

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Posted 15 January 2020 - 05:34 AM

Does anyone find that light pollution diminishes as the night wears on? As the general population goes to bed, turns off house lights, cars stop being driven, shops and factories shut down...


Yes, I have measured the effect frequently with my Sky Quality Meter. In or near cities, the skyglow typically falls by roughly 1/2 magnitude between early evening and the early a.m., after which it flattens out. The drop is less in semi-rural areas, but it's still quite substantial.


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#3 LDW47

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Posted 15 January 2020 - 08:33 AM

Up here in the wide open spaces of Northern Ontario in our small city of 50,000 since they installed LED lighting about 6-8 yrs. ago it is even more pronounced. From my back yard here in town all the major constellations are well defined even the Big Dipper, which hangs out over the city core, is no problem defining, on a good nite of transparency / seeing M 80-81 can be picked up with ease high above, what many call those d*mn LED’s ! I love LED lighting in comparison to the days of HPS / MV that shone like a spot light high into the night skies ! 



#4 happylimpet

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Posted 15 January 2020 - 11:11 AM

In Southampton the LED streetlights dim noticeably at 2355. I had some imaging across this time and noticed a ~5% drop in background level....obviously much of my light pollution isnt local. But some is.

 

It is definitely darker in the wee small hours than at, say, 10pm.



#5 PXR-5

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Posted 15 January 2020 - 12:24 PM

Yes!
By 2AM it's better, then by 4AM is much better.
I can't really explain why though.

#6 John Fitzgerald

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Posted 15 January 2020 - 12:28 PM

Lots of house lights, car lights, and storefronts turn off lighting after 10 PM, especially in the winter after the holidays.  In summer and during holiday sales it seems to go on a little later.  Christmas lighting makes LP noticeably worse here for several weeks before the holiday and a week after.


Edited by John Fitzgerald, 15 January 2020 - 12:28 PM.

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