Lights
All three light types. ( parallel, radius, spot light ) have options
for how shadows
from the light source is rendered.
You locate the lights property window the same as you do with objects. Right
click on a light or off the project window, by clicking on the light symbol.
On the property window there is a shadow tab.
The parallel light shadow option is only enable or disable cast shadow.
The radius and spot light have the enable or disable cast shadow.
This option doesn't determine how bright or how far the light will illuminate.
It sets how hard or soft the shadows created by the light will be.
Lower values will have hard shadows ( the edge of the shadow )
higher values will have softer shadows edges.
Here are some examples using a radius light:

Hard 0.000%
|

Medium 50.000%
|

Softest 100.000%
|