@jessethecockapoo
in video capturing mode all things is in auto mode then when you turn your camera to the dark side it's trying to set best exposure , ISO accuracy and balance for such a light reflection condition then you get higher exposure time and ISO so it will cause your dark side getting some noise and brighter than before and also your bright location in frame getting too much exposure actually being over exposure.now you see it can affect your video quality.some locations is too bright and some location with noise you have two options :
1-set your standing location behind the light beam source specially sun light coming in from windows when you standing behind the light source light beam will distribute and reflect from objects in the same ratio
2- using some filtering like ND in front of your lens to control the light density that coming into your camera sensor
you know its not your camera problem it was been issue and challenging to all optic system even for our eyes
hope this help