I recently bought an adjustable bed base which has USB ports on both sides. Each port has a bright blue light that illuminates the whole bedroom at night. I don't use them so covered both with black electrical tape. Problem solved. I've had the same problem with several desk lamps that lit up the world with that blue light even when turned off. I returned a couple of those immediately. But I looked through the review…
There's a brand on Amazon called LIGHT DIMS that sells differently sized stickers, in both ultra-dim and full-blackout forms, which do _exactly_ what they say on the tin, and it's amazing. I used the ultra-dim for the (white) temp display on my Dyson fan in my bedroom, and the blackout for the brighter-than-the-sun blue LED on my charger brick. Also used the dim one on a smoke detector because my 5-year-old thought i…
However after a while it became annoying to try to peel the small stickers off the backing, then fumble to center a small sticky thing over the offending LED.
so... I use painters tape. I started with the blue kind, but switched to black. Easy to tear or cut, easy to size. electrical tape isn't sticky enough.
I choose an appropriate number of layers for the problem.
Most lights just need one layer. Sometimes I need to kill the LED directionality to be acceptable. And some indicator lights need to be dim, not off. Think an HDMI switcher where you need to know which port is active, or router port activity lights.
Sometimes I put a second layer when I need less or no light.