brightness control inverter

[mhermens]

I have a magicmirror with a LM230WF5 (TL)(A1) panel, to control this i have installed a M.NT68676.2 LCD module with SQD-632 inverter module. which i have bought as pair.
when i want to adjust the brightness the strength of the led doesn’t change, the image seems to get whiter.
to explain it better i have included some pictures.
does anyone know what is causing this problem?

0% brightness

50% brightness

100% brightness