This display shows a Point Light, which is the most basic type of light available in UE4. A Point Light emits light from a single point in all directions, spherically. This is most obviously seen by looking at the light's radius, which is visible when the light is selected:
In the image above, you can see a pale blue wireframe sphere that surrounds the light. This shows the radius of the light, beyond which the light will have no affect on the environment. The falloff for the light will begin at the extents of this sphere and move inward toward the light Actor's position.