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Walking on the Moon

SQM reads the same but sky looks brighter?


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I was out last Saturday night imaging from my usual spot and although the SQM meter was indicating pretty much the same as usual (circa 20.80) things just didn't seem very dark at all to the naked eye.

Conditions weren't perfect as there was a slight bit of haze but no worse than what I'm used to.

I could make out the cloud of the Milky Way but again it just didn't seem very bright, almost washed out like someone has been adjusting the contrast/gamma.

What has changed is that the street lights have changed from sodium vapour to LED so could it be more of a perception thing?

Also I was using different imaging kit to usual so I couldn't compare previous subs to this session to see if it was better or worse.

I thought that an SQM reading would go lower as the sky fog/glow increased but as I said it was pretty much where it usually is.

Any thoughts?

PS...one other thing that has changed is that I'm getting older but I'd have thought that would make the view dimmer not brighter 😂


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Along with the VIIRS satellite, SQM meters under read high temperature LED light. So if your street lights have gone from sodium to white LED, then yes the SQM meter will not truly represent your visual impression.

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Things get brighter (perceptually) when you get dark adapted.

Maybe change of lighting helped to get better dark adaptation (leds are usually directional rather than omni directional).

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I'll take them both onboard @vlaiv and @AstroKeith as I'm sure they both play a part in it.


Of course this thread (that I missed) may also play a big part in it.


I equate my experience to looking at those washed out LCD monitors of yesteryear where there was no real black and the contrast was poor.

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