The lightning shield was a fictional type of impenetrable deflector shield within the The Adventures of Captain Proton holoprogram created by Tom Paris. It was used by Doctor Chaotica to protect his base of operations, the Fortress of Doom, from his enemies. This included his nemesis Captain Proton and photonic lifeforms which the program believed to be from the fifth dimension, but were in fact real.
To assist the photonic lifeforms in defeating Chaotica, the crew of the USS Voyager played along with the program and sent Queen Arachnia, played by Captain Kathryn Janeway, to seduce Chaotica and disable the shield from within. This proved to be successful. (VOY: "Bride of Chaotica!")