St. Elmo's fire is a true corona effect, and is remarkable and looks like an envelope of glowing gas, because that is what it is. I have seen it on the wings of my airplane once, it is beautiful and ghostly. Note that the explanation of St. Elmo's fire discusses the need for the ship to build a strong electric field relative to its environment. This is what Lu has been saying, and is one possible source of light, were the aircraft not grounded.
The stuff that we see in night dusty operations is not St. Elmo's fire. The bright sparkles are each discrete particle of sand emitting light when it is struck by the blade. The blade is going about 450 knots in a hover, quite enough to shock the sand into glowing (which also hits the blade hard enough to erode it harshly).
Note the flashes at the rotor while the aircraft is grounded. St Elmo's fre is quickly wicked off when the bonding system of the aircraft is touched to ground. Look at the left landng gear to see the grounding wire. Also, note that the flashes only occur when enveloped in the sand.
In many events that I have observed (and in the posted photos) you can actually see the scintillation from each grain because the lights are not a gas corona but rather a sparkling mass of points of light, each a particle of sand that is emitting light.
The scratched crystal in the site I posted is a direct example of this type of light.