Understanding light pollution

[BS269]

I live right on the edge of bortle 4/5 skies, with a sky quality of 20.47, according to the clear outside app. I live in a national park but the light pollution from Manchester is what makes it so supposedly high. However the closest significant local light sources to me (street lights, multiple houses etc) are probably about 1km away (and even further in most other directions).. which leads me to my question. Given the little local light pollution around me, is it possible that my seeing conditions are better than bortle 4/5? Or is this the best it can possibly be and local light sources only make it worse? Is bortle 4/5 skies worth getting light pollution filters? I intend to do visual and all types of AP.
 

I only started this hobby in may and not had many opportunities to actually Do much stargazing, but when I have I’ve been able to see quite a lot of stars, given it never seems to get truly dark this time of year. I imagine it will only get a great deal better come autumn/winter.

Cheers!

[Captain Scarlet]

If you look on lightpollutionmap.info, select atlas 2015 and click on your location, you’ll get a very good indication of the best sqm value you should expect at zenith. I have collected lots of actual sqm-l data from two very different locations and that website is spot on for both of them.

[BS269]

I have had a look at this map before and it gives my sky quality as 20.44, so very similar. I was just wondering if the lack of very local light pollution could have improved it or not. Hopefully I should still be able to see some impressive views!

cheers

[Waddensky]

The Atlas 2015 map is based on a calculation of light pollution levels from satellite data, not on actual measurements. Clear Outside uses the same source as lightpollutionmap.info. Sky glow can be caused by scattered light from distant sources as well as local lights. Light pollution filters don't help much.

The best way to determine your actual sky darkness is performing measurements yourself using an SQM or by finding out your naked-eye limiting magnitude using suitable charts.

[Tenor Viol]

I live on the outskirts of a small market town in Shropshire. LP is classed as '4' here. Most of the street lighting is low pressure sodium and a substantial part of it (not all) goes off about 11.45pm. Milky Way is readily visible when it's clear. There is no major town to the south for over 20 miles, and about 15 for west and north, and nearly 30 to the east.  Skies don't noticeably improve until you move deeply rural into Wales. 

Class 4 skies are pretty decent and I don't think you need to be too aggressive about filtration. I'm still waiting for key pieces of kit to arrive and I am going to experiment photographing with / without filters, but I am going to avoid say CLS-CCD as I don't think I need that level. I thin as long as I can filter out sodium D line it will be OK.

[wookie1965]

This what I have to put up with complained to the council they put a shield on this is the result , not worth a carrot

[PoI-LordBlackwood]

Ah finally light pollution

For someone who lives in Bortle Class 8 skies and near-constantly cloudy weather, it's almost a miracle when the clouds clear at around 12 to 1 am. We have it quite hard here and most of us have either resorted to looking at the brighter DSOs or getting light pollution filters. 

4 hours ago, Waddensky said:

Light pollution filters don't help much.

Could I ask, would they help reduce the pollution to around a Bortle Class 5-6's worth? If so, I might just consider...

Cheerio and Clear Skies 😀

[Kyle Allen]

I think Light Pollution Filters only work if the main source of light pollution is from sodium street lights. All filters work by blocking certain wavelengths of light and allowing others to pass through. This results in a dimmer image but higher contrast. Sodium street lights can be filtered out because they only emit light in the orange part of the spectrum but newer LED street lights emit light across the whole spectrum so can't be filtered out.

[dd999]

I had a similar question - I live in what is showing as a Bortle 4 area, but almost next door to us is a hospital with three large flood lights on all night long....and frustratingly towards the south from my back garden.

How much of an impact to the sky visibility would this usually cause? ... does this type of impact reduce you down a bortle or two?

Do light pollution filters help filter out this type of light as well as street light glow?