I guess compared to blackout curtains/blocking leds/draft stopper/synced partner when you wake up you could have natural sunlight in the room. ( "Participants were asked to sleep with open shutters/curtains for the entire duration of the study.")
But they didn't test for that here.
The studies conclusion seems to be blackout curtains either cost $$$ or take a bit of effort to install, mask is cheap/easier.
Sleep is good, people sleep better when as much light is blocked as possible. It's a conclusion that is known.
And by contrast, perhaps just as important to get plenty of natural light during the day to regulate melatonin production - an anti-cancer and immune system enhancing agent whereas artificial light at night can be a real problem.
https://cmbl.biomedcentral.com/articles/10.1186/s11658-022-0... and many other reports.
But they didn't test for that here.
The studies conclusion seems to be blackout curtains either cost $$$ or take a bit of effort to install, mask is cheap/easier.
Sleep is good, people sleep better when as much light is blocked as possible. It's a conclusion that is known.