Lots of customer encounter the problem where night vision is dark on the one side and light on a object or other side.
Problem is camera placement. Camera cannot be placed next to a wall and has to be moved at a different angle. This happens to ALL infrared night vision cameras, does not matter the brand. Same happens if there is glass windows. Also note, very important, if there is a big tree, bush or anything in front of camera, the same thing will happen. The tree will be illuminated, but the areas around will end up being dark. CAMERA PLACEMENT is MOST IMPORTANT.
Secondly, if there is not obstacles in front of camera, and night vision appears to only work short distance, take note this is a chipset specification. If it is entry level chipsets, they work on a higher level lux and needs lots of light to function, e.g. 1 lux. This means the camera's iris only allows a certain amount of light through and there is very few methods to improve this with infrared. Best is to have a light outside as well. If it is our Sony CCD range of cameras which have a lower lux, the infrared distance will improve dramatically since this is 0.1lux and lower. With these higher spec cameras you can achieve respectable infrared distances. This is why most of the entry level 1mp cameras can only effectively do 15m to 20m infrared (since they are 1 lux) and we as manufacturer dont put stronger infrared lights on them since the effect is not worth it.