Inverse Squared Falloff
These lights also use Inverse Squared Falloff, which is a setting found in the light's Details panel under the Light Advanced category.
This is a realistic calculation of how fast light falls off as it escapes its source. Incidentally, this is also a very fast falloff rate, requiring the light radius to be high. This is important to keep in mind, as there is currently a limitation of no more than 4 shadowing stationary lights overlapping at one time. When boosting light radius to compensate for inverse squared falloff, it is easy to make several lights that overlap.
For more information, please see the Stationary Lights documentation.