Typically cylinder lights are used to simulate fluorescent tube lighting
The cylinder light shape simulates light from a cylindrical area source (tube shape).
Along with the settings that are common to all lights, this light also has the following parameters:
Increasing the size of the cylinder light will create a larger area light size and therefore will soften the shadows that run perpendicular to the cylinder’s axis. Cylinder lights will always be circular. It is not possible to scale the width to create an ellipse.