The size of the ceiling should be 20 cm high from the wall, 30 cm or 35 cm wide from the wall, and a few are 40 cm light troughs. The width outside the baffle is generally about 8 cm, and the width of the light trough is 10 cm or 12 cm, which is generally determined according to the width of the whole ceiling. If the ceiling height is high, the high fork will be larger, and if the ceiling height is low, the height difference will be smaller.