Night light is easy to fake with upward-facing illuminators.

Any good metric ceases to be meaningful once it’s actually used as a metric, because that’s when the gamification starts.

It's kinda hard to hide that you are faking it on a national scale. Way easier with GDP.

Additionally the modern trend, in many types of public lighting, is to reduce the amount of light which shines upwards in order to increase efficient and lower light pollution.

I was hesitant to mention this, but yes, it run counter to widespread initiatives to reduce light pollution

Or perhaps measure other forms of pollution?

Possibly, but also assuming it's an actually sophisticated analysis and not an naive one, like the Martinez Democracy vs Autocracy study that western MSM loves to peddle. NBER (one of top eco think tanks) did a sophisticated night lights study of PRC in 2017 - same year as OG Martinez study using naive methodology as Henderson original work from early 2010s - and found PRC's reported GDP was actually _underestimated_ using night light data. But for obvious reasons this study by multiple staff economists at the FED doesn't get any attention in western MSM, but one by an assistent prof of public policy somehow does. Almost as if it's good self marketting considering Martinez keeps updating study with same rudimentary methodology every few years to get clicks.