Out of all the towers, the West Tower remains the most untouched, keeping much of what it was when the school was first founded, with only the occasional need to widen the building to accommodate the larger amount of students over the years. Keeping the lighting the same as it's ever been, magic has been used to help maintain the lighting of this area.
The sole exception would be the updated Horned Serpent Common rooms which are found in this section which features more modern designs and means, it looks as if it was shoehorned into this otherwise classical design.