If the night vision on your camera is very dim or non-existent, it may be a defective I.R. board, but that is unlikely.

You can think of I.R. lights as a flashlight. When you point that flash light up at the sky, you will not see the light illuminate anything. This is the same way with night vision cameras. If you point your cameras parallel to the horizon, they won't illuminate anything. You want to make sure to point your cameras downwards so that the I.R. lights will allow you to see the ground.

In most real-world scenarios, the general rule of thumb is to reduce the specified IR viewing distance by a third. For example, if a camera’s IR viewing distance is rated at 50 feet, it will be able to produce a clear nighttime image at about 34 feet away and the IR illumination will begin to fade at that half-way point. If you were to put the same camera in a room that is pitch black, point it directly at a wall and move it back 50 feet, you should be able to see that wall.