some dwarf hair grass grows just fine in medium light . I actually planted some in a tank half a year back. My grandpa thought to "save electricity" and turned off the light I had on a timer completely. growth slowed significantly on the dwarf hairgrass but it still grew with no vertical growth.
In my own setups I have dwarf hair grass grown under med-high light and no CO2. it is sending out runners and filling out at quite a decent speed.
dhg likes to remain rooted in the substrate and once rooted, rarely sends out runners that stray from the substrate.