VIZIO OLED H1 TV picture is too dark or keeps dimming

The checks in more detail

Choose Standard or Vivid for a bright room, and Calibrated Dark for a dim one, to compare. Raise the Backlight control, which on an OLED sets the panel brightness, and the Brightness and Contrast controls. Turn off the Eco Mode and the Ambient Light Sensor, which dim the picture as the room or the content changes, and Active Full Array if it is shown for your settings. Check the Black Detail and Adaptive Luma controls, which affect shadow detail. Then HDR and the source. An HDR source needs the HDMI input set to the full format, which VIZIO calls HDMI Mode or Full UHD Color, so that 4K HDR is carried;

turn it on for the port. HDR content is mastered for a dark room, so it can look dark in a bright room; use the HDR picture modes, which are brighter, and reduce the room lighting. On a streaming device, set the output to HDR and Dolby Vision where available. Remember that a brief dimming when a bright scene fills the screen is the brightness limiter, which is normal on every OLED. Keep the screen clean and avoid reflections. A dim picture on every source in a dark room with the settings correct may mean an aging panel; contact VIZIO support with the model number and the serial number. SmartCast has a few of its own quirks that affect a dark picture.

The Picture menu can store separate settings for each input and for each app, so you may have fixed the picture on one input and found it dark on another; check each. The TV offers a Reset Picture option for each mode, which is worth using after experiments, and an Auto Brightness feature on some builds that follows the room. A casting session from a phone sends a picture whose brightness is set by the phone, so a dim Chromecast picture can be the phone's own setting. VIZIO's OLED is the only self-emissive panel in the line, so the diagnosis differs from the LCD models, which have a backlight to turn up.