There’s a hidden way to do it. If you select the landscape, go into landscape edit mode(shift +3) then click on manage. Use the selection tool to select all of the landscape components. Next exit landscape mode and go back the default Place Mode (Shift +1) Then click on the Details panel and in there you should see the “affect distance field lighting” check box under the Lighting section.
This is a workaround I use for materials that use distance to nearest surface on older GPU’s will cause weird artifacting.