Eror: Different Brightness Settings

[ard4wien]

My monitor (W2243), connected via a VGA cable, becomes completely bright when I set the brightness value to 0, and it becomes dark when I set it to 100 (I think this is how it should work). However, my second monitor (SL3230T), connected via HDMI, is bright when the brightness value is 100 and dark when it is 0. How can I solve this?