This one is actually very interesting. For one its not a lens flare because they are always round or oblong.
Its not a reflection, notice that the shape of the light on top of the door and behind the door is uniform. If it was a reflection the light behind the door would be offset slightly and perhaps a bit bigger or smaller.
Its not dust, because dust generally exhibits a bright border with slightly dimmer inside. And also usually has a round shape. And this shape is brighter on the inside than outside.
That leaves a few options.
Edit picture - possible but doubtful.
Motion blur on some fast moving object.
Some form of natural vapor or smoke.
Some form of paranormal vapor or smoke.
My gut feeling is that its not paranormal, its too regular shaped. But I can't figure out what it is. Got me stumped.