Neutral Density:
The neutral density actions will attempt to add density on
your photographs through the use of curves and a layer mask,
this way only the bright parts will be affected.
ND 0.3 will reduce the bright parts by 1 stop
ND 0.6 will reduce the bright parts by 2 stops
ND 0.9 will reduce the bright parts by 3 stops
ND 1.2 will reduce the bright parts by 4 stops