Gradient’s parameters:

The next circle will be created with the same tool.

Blending Options-Gradient Overlay

Gradient’s parameters:

Applying the known instrument you can insert another circle with the sizes indicated below.

Blending Options-Gradient Overlay

Gradient’s parameters:

Take a brush with blurred edges now of white color and insert a flare on the lowest part of the circles situated on the central part of the luminescent screen.