A TCL 5-Series S555 picture that looks too dark is usually a setting, a source that is sending a dim signal or the effect of the TV's power saving, because this QLED has the brightness to look vivid and rarely loses it. Press the star button on the Roku remote and open Picture settings. In the Picture mode, Movie and Dark room modes are deliberately dim, and Normal or Vivid are brighter, so check the mode first. Raise Backlight, the control that sets the light level, and not Brightness, which lifts the blacks; then check Contrast.
The checks in more detail
Look for a setting called Energy saving or Auto brightness in the TV's system settings, which dims the screen in a bright room or to save power, and switch it off for a test. An ambient light sensor, if the TV has one, can also dim the picture when the room is dark. Next look at the content. HDR shows are made for a bright display and often look dark if the TV is in a mode that does not suit them, so choose the HDR picture mode when an HDR signal arrives, and check that the source device outputs HDR correctly;
in the Roku settings, a display type option can be set to 4K HDR. A streaming app with a dim picture may have its own brightness or data saver option. On a game console, make sure the HDR calibration is done and that the TV's HDMI input is set to the enhanced format for 4K HDR. A cable that is not rated for 4K HDR can force the device to drop to a dim signal. If the whole picture is dark in every input and even in the menus, the backlight may be dimming or failing.
Use a flashlight to look for a faint picture: if you can see one, the backlight is off or has failed, and that needs service. Also let the TV warm up for a few minutes, since some panels start dim. Update the TV, because brightness behavior changes in software, and run a factory reset if all else fails. The S555 is a QLED with modest local dimming, so dark scenes will never be as deep as on a Mini-LED set; that is the design and not a fault. If the picture is truly dim on all sources, contact TCL with the model number and serial number.
Differential
Likely causes of “TCL 5-Series Roku TV S555 picture is too dark or keeps dimming”, and how to tell them apart
- 1
A dim picture mode
What separates it Movie or Dark room is selected
How to confirm Choose Normal and raise the Backlight
- 2
Energy saving or auto brightness
What separates it The picture dims by itself
How to confirm Turn them off
- 3
HDR content in the wrong mode
What separates it Dark HDR shows
How to confirm Use the HDR mode and a rated cable
- 4
A source sending a dim signal
What separates it One input is dark
How to confirm Check the device's settings and cable
- 5
A failing backlight
What separates it A faint picture under a flashlight
How to confirm Contact TCL
Before you touch a setting
Record this first — changing settings destroys the evidence
- The picture mode
- Whether energy saving is on
- Which input is dark
- Whether a faint picture shows under a flashlight
Try in this order
0 of 6 completedCheck the picture mode
ReversibleNormal is brighter.
Raise the Backlight
ReversibleNot Brightness.
Turn off energy saving
ReversibleAnd auto brightness.
Check HDR settings
ReversibleAnd the cable.
Update the TV
ReversibleIn System update.
Use a flashlight
ReversibleTo test the backlight.
Model-specific
What is true of this model and not of its siblings
- QLED tier
- It is bright but has modest dimming.
- Backlight
- The control that sets the light.
Stop boundary
When this stops being a self-service repair
- !If a faint picture shows under a flashlight, contact TCL
- !If every input and menu is dark, contact TCL with the serial number
- !Update the TV
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why is my S555 picture dark?+
A dim mode or energy saving.
Backlight or Brightness?+
Backlight sets the light level.
Why are HDR shows dark?+
They need the right mode and cable.