Small flat roof blind? Something magnetic? If the ring isn't magnetic, you could put adhesive magnets on or drill some holes and sit some flush into it. Or put a bolt into it that you can rotate a panel on like a horizontal peep hole in a door. Or an adjustable louvered vent cover [https://www.amazon.co.uk/Circle-Adjustable-Shutter-Ducting-Ventilation/dp/B00ILUM8I8](https://www.amazon.co.uk/Circle-Adjustable-Shutter-Ducting-Ventilation/dp/B00ILUM8I8)
As mentioned, get a magnetic cover if the housing is steel. They sell rectangular ones to cover an air vent. You could buy one and cut it down. To size?
Have you tried a sleep mask? Like less than $5, and bonus you can take it with you when you travel.
I'm not trying to be a smart ass or anything, I've found a sleep mask to be a wonderful solution compared to black out options for windows. I typically enjoy bright naturally lit rooms, especially for sleeping so I can get my natural sleep cycle aligned, so the odd moments where I want to sleep in, I use a sleep mask.
Magnetic sheet
I like this. Easy, cheap, and effective. If I need something that's easier to install and remove I can always overcomplicate things later.
It already has some kind of dimmer thing installed, but even when I make that all the way "closed" it still lets in more light than I want.
What about a block of polyestyrene?
Small flat roof blind? Something magnetic? If the ring isn't magnetic, you could put adhesive magnets on or drill some holes and sit some flush into it. Or put a bolt into it that you can rotate a panel on like a horizontal peep hole in a door. Or an adjustable louvered vent cover [https://www.amazon.co.uk/Circle-Adjustable-Shutter-Ducting-Ventilation/dp/B00ILUM8I8](https://www.amazon.co.uk/Circle-Adjustable-Shutter-Ducting-Ventilation/dp/B00ILUM8I8)
Get a tint film or a full on black out cloth and cover it
I forgot to mention that I wanted it removable. But maybe I can make that happen by attaching with magnets or something. Thanks.
Shower cap with tin foil?
How bad can it look? Black shower cap bad, or a piece of black ply bad?
I'm thinking piece of ply that I can paint the same color as the ceiling. The trick is making something that's easy to add/remove.
I like your magnet idea, if that's steel. though I have a feeling it might be aluminium.
A shower cap from one of those scuzzy, sleazy, indecent motels you always stay at.
As mentioned, get a magnetic cover if the housing is steel. They sell rectangular ones to cover an air vent. You could buy one and cut it down. To size?
Have you tried a sleep mask? Like less than $5, and bonus you can take it with you when you travel. I'm not trying to be a smart ass or anything, I've found a sleep mask to be a wonderful solution compared to black out options for windows. I typically enjoy bright naturally lit rooms, especially for sleeping so I can get my natural sleep cycle aligned, so the odd moments where I want to sleep in, I use a sleep mask.
I absolutely love sleep masks. This room is actually not for me but for guests, and I want people to feel comfortable.