The luminaire adopts a rotationally symmetric reflector, and the symmetrical axis of the light source with rotationally symmetric light distribution is installed along the reflector axis. The isointensity curve of this kind of lamps is concentric. When this kind of projection lamp is illuminated by a single lamp, an elliptical spot is obtained on the illuminated surface, and the illumination is not uniform; however, when multiple lamps are illuminated, the spot overlaps with each other, which can produce satisfactory lighting effect. For example, hundreds of rotationally symmetrical projection lamps are commonly used in stadiums, which are installed on the high towers around the stadiums to obtain high illumination and high uniformity lighting effects.
There are two symmetrical planes in the isointensity curve of this kind of projection lamp. Most lamps use symmetrical cylindrical reflector, and the linear light source is installed along the axis of the cylinder.
The equal light intensity curve of the lamp has only one symmetrical plane. The luminaire is made of asymmetric cylindrical reflector or symmetrical cylindrical reflector plus grid restricting light. The most typical is the sharp cut-off block retracted light distribution. This kind of light intensity distribution single lamp can obtain a more satisfactory illumination distribution.
There is no symmetrical plane in the isointensity curve of this kind of lamps. It mainly uses the mixed light lamps with different kinds of light sources with different light intensity distribution and special lamps designed according to the specific lighting requirements of the place of use.