If all you want is a glowy sphere, then set the radius of the light same as the sphere’s and set Min. Roughness to default value(0.08). But it is best to set Min. Roughness to 1 if you want area light kind of effect and reflections with non-spherical shapes. Also don’t forget to disable inverse sqaure falloff as i mentioned before. Example here;
I’m moving this thread to Rendering section, btw. It suits there better i think.