With a brief rendering time of only 2minutes, we can afford to increase the number of lights to smooth out the shadows. With LUMEN this is quite easily accomplished. Click on the Sphere object, and change its Segments from 24 to 48. You'll see the number of spotlights in the editor window jump up in number.
Because the number of lights has increased, we need to decrease the brightness that each light has. Click on the Light object in the LUMEN hierarchy, and under the General tab, reduce its brightness from 100 to 20. Lets widen the area the light is shining on too — go to the Detail tab, and change the inner angle to 30, and the outter angle to 60. This will have two effects: it will soften the shadow maps a bit by spreading them over a wider area, and it will brighten up the scene some. Render, and lets look at the result.
We have very smooth shadows now, nearly as smooth as Global Illlumination. If we had textures on the floor and object, chances are the remaining artifacts would be invisible. Alternatively, increasing the shadow map Sample Radius can help smooth out the remaining artifacts on the floor. Be wary though... shadow maps can have a tendency to leave dark halos around detailed areas — an effect that is creeping into the sample image here.
The final render time for this image is only 13min 51sec, nearly half that for the Global Illumination Render. Roll over the image to compare the two techniques.