Question

why is it generally advised that every living room must get direct sunlight at least for a short time

Answer 1

as under higher temperature like 110 degrees bacteria get destroyed therefore after continuous supply of heat the particular room will get heat and bacteria will get destroyed

Answer 2

Living room is an area where the people in the house spend most of the time. It is important to keep the room dry and warm instead of being fungus infected and damp. Sunlight being the natural disinfectant, keeps the fungus away, provides dryness to the wall, floor and the room and hence beneficial to the health of the people. Moreover, sunlight provides the  vitamin D which is essential for the growth of bones and thus contributes to healthy living.