Check the camera model again, the DS-2CD2147G2-SU is a ColorVU and does not have IR, which can reflect in night mode. Nonetheless, if it's something with IR, like the DS-2CD2146G2-ISU, you might try adjusting the camera module to point it in a slightly different direction, where the IR LEDs won't overlap the housing, and not toward a wall or other things from which IR can reflect. Another thing is to correct the rubber band at the lens as mentioned by ludshed.
Or just move it inside and use bullet/turret outside, much friendlier casings, dome can be really painful and im using it only when theres a need for IK10 rating.