I have a Roku Ultra, connected into the HDMI 2 input on a Sony 55" TV. Everything was working fine and now suddenly when the TV input is changed to HDMI 2 for the Roku, the screen is dimmed considerably.
I have tried EVERYTHING including a factory reset of the Roku and I cannot figure out how to adjust the brightness up on the display.
I finally solved the problem by completely resetting the TV to it's original factory settings, in effect a complete "re-boot" of the TV. It was a bit of a pain, because I had to re-establish the connections between the TV and the cable system wi-fi, as well as reset the connections with Amazon Prime, Netflix etc, as well as the Roku.
But that fixed the problem and so far I haven't had a relapse.
Unfortunately, that did not work for me. If I turn it off and back on it is bright for a few minutes and by the time I pull up a show it is back dim. Very frustrating. At this point I may return it and try another streaming device.
Did you do a full factory reset or initial settings restore on your TV? That's what I had to do. The command was somewhere in the settings menu on the TV I think. If that's what you did and it didn't work, I'm out of suggestions.
On my LG TV, the issue is that different picture settings can be set for each input source (e.g., Roku, DVD player, Xfinity receiver). When I originally set up the TV (using optimized picture settings from Consumer Reports), I set it for all inputs to use the same settings. However, I discovered that when I plugged in the new Roku, it used different picture settings that made the picture much brighter. The other inputs retained the old settings. Instead of having to reset the TV to its original settings, I was able to use an input other than the Roku input and then use the option to set all inputs to use the same settings (under Advanced Picture Settings).