If it's not Photoshop (it can be) you will need:
* a long exposure
* a white laser pointer that will be used to "paint" during the exposure
* and a lot of patience
edit // I think this may be mostly Photoshoped because of some details:
(1) The light must be "on something". In that top zone, the light is just "in air".
(2) Uncompleted reflections
It may be painted with long exposure but completed with Photoshop.