Illuminars are classified in 5 categories according  the ratio of the luminous flux emitted by the upper and lower half spaces of the illuminar.

　　(1) Direct luminaire

　　Most of the luminous flux (90%~100%) of this type of luminaire shines directly downward, so the luminous flux utilization rate of the luminaire is the highest. However, due  the large differences in the shape, material and processing of the reflecting surface, or the different devices on the exit surface, the emitted light distribution may be wide or concentrated, with many changes.

　　(2) Semi-direct luminaire

　　Most of the luminous flux (60%~90%) of this type of luminaire is directed  the lower half of the space, and a small part is directed  the upper half of the space such as the ceiling or upper wall. The upward component will improve the brightness ratio of each surface in the room.

　　(3) Diffuse or direct-indirect luminaire

　　The upward and downward luminous flux of this type of luminaire is almost the same (40% ~ 60% each).

　　(4) Semi-indirect luminaire

　　The upward luminous flux of the luminaire accounts for 60%  90%, and its downward component is often only used  produce brightness commensurate with the ceiling. o much of this component or improper distribution can also cause defects such as direct or indirect glare.

　　(5) Indirect luminaire

　　Most of the luminous flux (90%~100%) of this type of luminaire is upward. If designed well, the entire ceiling becomes a lighting source, achieving a soft and shadowless lighting effect. Since the downward luminous flux of the illuminar is very small, as long as the arrangement is reasonable, the direct glare and the reflected glare are very small. The luminous flux utilization rate of this type of luminaire is lower than the previous four types.