There are 3 kinds of Flat Design Long Shadows.
- simple and unrealistic (needs to be in a container as shadow doesn't fade)
- fading shadow which ends in a flat line (using blend with straight lines 1px apart, 2nd line opacity set to 0%)
- fading shadow which ends in the shape of the object casting the shadow (using blend with "casting" objects 1px apart, 2nd objectopacity set to 0%)
In both 2. and 3., you overall opacity of the blend can be adjusted if it is too strong going from 100-0% (which is obviously true for the simple method 1.)