I think some OLED displays don't have backlights? On manipulating the backlight to display a dark scene more power-efficiently: my TV that does this, if there'

I think some OLED displays don't have backlights? On manipulating the backlight to display a dark scene more power-efficiently: my TV that does this, if there's a small region of constant color (e.g. a TV station's logo) its brightness wavers noticeably as the rest of the scene changes.