Wikipedia
Dark Lightning is a very strong, invisible by-product of thunderstorms in the Earth’s atmosphere. Much like regular lightning, dark lightning is created from the natural process of the buildup of electrostatic charged particles within clouds, trying to cancel out opposing charges and naturally occurs in thunderstorms. However, two main features of Dark lightning drastically separate it from regular lightning. These two factors are that Dark lightning is, in fact, invisible to see with one's eyes and doesn’t radiate any heat or light whatsoever, as regular lightning does. Instead dark lightning releases bursts of gamma radiation (gamma rays). The gamma rays created by dark lightning are from large clouds of positrons within thunderclouds, which do not immediately react and producing gamma rays. [1]
Much speculation is made by researchers as to the purpose of dark lightning. One of these predictions as to the reason for dark lightning's existence is that it may be competing with regular lightning during thunderstorms as a pathway for clouds during storms to give off their energy.
Usage examples of "dark lightning".
The sun crawledout from the dark lightning-shot cloudbank to blaze tri-umphantly in the blue sky.
The ground seemed torn everywhere now with the dark lightning strokes of rifts, heaving themselves open widely to the accompaniment of awful groans and screechings.
The wyvern's long, barbed tail whipped toward the griffin like dark lightning.