Here are some darkness readings I took with my SQM-L device (at zenith) on my visits to the Rocky Mountain Star Stare (darkest ones each evening):
21Jun'17 => 21.9 magnitudes per square arc second (MPSAS)
22Jun'17 => 21.8
2018 => smokey, cloudy, rainy, 1 hour good observing (I decided to stay home)
26Jun'19 => 22.0 MPSAS
27Jun'19 => 21.9
28Jun'19 => 22.0
03Sep'21 => partly cloudy with approaching fog
04Sep'21 => 21.7 MPSAS
05Sep'21 => 21.7
22Jun'23 => 21.75 MPSAS
(I left early because of allergies and a cloudy/rainy forecast.)
Note that 2017 & 2019 were during the solar sunspot cycle minimum, whereas now we are approaching the solar sunspot maximum, meaning skyglow is much greater from the increased ionization of our upper atmosphere caused by the increased solar wind. The 2022 readings started to show this effect as the solar cycle was leaving its minimum.
I would guess that readings in June 2025 will be around 21.5 MPSAS; noting that this is a worldwide situation of increased sky brightness that needs a few more years before the sky is darker.
