hikvision IR at night

hi, just after abit of information really, ive set up my -

1. HIKVISION DS-2CD2355FWD-I | 4MM
2. S-2CD2T55FWD-I5/B | 4MM

all work perfect during the day and even at night but ive noticed i cant see any licence plates as it seems over exposed is there something im missing in the camera setting, ive tried speeding up the shutter speeds but seems to wash out the image completely.

any advise will be greatly appreciated...

hikvision IR at night