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Display Brightness
Brightness setting of the screen (0-255).
If the safeguard is enabled, levels less than 20 will be set to 20 to prevent accidental black screens.
Ignore Current Level: if it looks like it's already at the required level, go ahead and set it again anyway.
Immediate Effect: ensure the change takes effect immediately. If not selected, it may not take effect till Android registers the new value, which may require a display on-off.You may that find Immediate Effect disrupts some applications.
Immediate Effect is only needed on Android versions up till 4.4.
If you have auto-brightness controls on your device, it's advisable to disable them before attempting to set the brightness manually. See system settings or Tasker action Auto-Brightness.