Decided to test this out since I finally got Darkness Sorcery maxed and I haven't seen anyone try.

Looks like the 100% Elemental Resistance ignore on the skill works on Physical Resistance as well. Other than that 100% ER Ignore, the skill gives 40% defense ignore, but I would doubt that alone will increase my damage 3x. There's also a difference of 1 orb on Blessing of Darkness in the screenshots below but it still wouldn't add this much.

Range is ~17.5k in the screenshots below using level 11 Light Reflection

without level 30 Darkness Sorcery

with level 30 Darkness Sorcery