How does the camera switch to night-time IR mode?  A discrete sensor or from an analysis of the picture content?

I'm attempting to overcome a problem where most of what I'm trying to monitor is in near darkness but there is a light source that only occupies the top two (small) corners of the picture. This two small areas of light prevent the camera from switching from day mode to night-time IR mode. This results in the majority of the picture being too dark to be seen during the night.

Is it possible to mask out these areas so they are not considered part of the scene and do do contribute to the false detection of daylight?