You definitely need at least 150 watts of led light to compare with a 400 watt hps and on top of that you need a full spectrum LED grow light.
From what Ive been learning so far is that:
150w led = about 400w hid
300w led = about 600w hid
600w led = about 1000w hid
The important this is to get a LED grow light that's really bright and powerful and provides a full spectrum light in order to get comparable results.