[Q] Lockscreen brightness very low topic

I'm on Carbon rom now (previously cm10,cm11,aokp,beanstalk, gummy, in all of them the same problem occured) , and for some reason the same wallpaper is much darker when on screenlock than on homescreen or the picture itself.
I read that disabling Ripple Effect on the touchwiz rom fixes this issue, but since I'm using a custom rom I don't have this Ripple Effect option anyway,
So does anyone know how to fix this?

Thanks !