Despite its diminutive size, the white LED on the end of the Dell AC511 USB SoundBar lights up a dark bedroom surprisingly well:
That’s pretty much the only power-on indicator for the streaming players, so I didn’t want to just slap a strip of black tape over it. Instead, because white LEDs don’t emit much energy toward the red end of the spectrum, I made a cute little filter from a snippet of Primary Red gel filter material, surrounded by a black Gorilla Tape donut:
Two layers of Primary Red cut the light intensity to a dim glow that’s barely visible in daylight and completely inoffensive at night:
The blue activity LED on the SunFounder got the black electrical tape treatment, however, with just a sliver showing through to give a hint that it’s still active:
One of the other WiFi adapters has a pinhole over a red LED that’s barely visible. Another, seemingly identical one, lacks the red LED under the pinhole; when I asked the vendor about that, I was told it was removed “to save power.” Yeah, right. That was part of the motivation to try a different adapter next time around, with good results.
Of course, you must wrap an opaque black case around the Raspberry Pi to tamp down the red and green LEDs on the PCB. It’s possible to control them in software, with varying degrees of difficulty depending on which Pi you have, but …
The Smell of Molten Projects in the Morning 
OK, it gives me a small sense of relief to learn I’m not the only one who does this. Back in the day when my AV receiver faced me, every LED lit in movie mode was covered. Added benefit: If you could see red, you knew a setting was wrong.
Side story: My youngest got to learn about negative decibels at an early age. That was the unit on the volume knob; silent was -Inf and full power was 0. He got up early and wanted to watch some TV without waking us up, so set it to “0” and powered everything up.