Uniform Spherical Distribution (Photometric Lights)
Uniform spherical distribution, as its name implies, casts light equally in all directions.
Create panel > (Lights) > Photometric > Click Target Light or Free Light. > General Parameters rollout > Light Distribution (Type) group > Choose Uniform Spherical from the drop-down list.
Uniform spherical light distribution
Viewport representation of a Target light with uniform spherical distribution