4. A circular room has a diameter of 12 m and a side-wall height of 10 m. The ceiling is a diffuse transmitter (transmittance equal to 0.3), which allows daylight goes into the space. a) Daylight produces 20,000 lux on top of the ceiling transmitter, what is the exitance of the ceiling transmitter? b) What is the luminance of the ceiling transmitter viewed from inside of the space? c) What is the luminous intensity at the normal direction of the ceiling transmitter? d) What is the direct horizontal illuminance at the center of the room on the floor? e) If the reflectance of the ceiling is 0, the wall has a reflectance of 0.5 and floor has a reflectance of 0.3, what is the final average illuminance at the floor? (Fcf= 0.22)