Force lightning, also known as Sith lightning, was a power that Force users could conjure through the dark side of the Force.
Why Couldn’t Darth Vader Use Force Lighting? Despite being an immensely powerful dark side ability and the fact that other Sith in cybernetic suits, like Darth Malgus were able to use Force lighting, Darth Vader never did. This was mostly because of his specific suit.
Vader’s master, Darth Sidious constructed his suit in a way that would cause as much pain and suffering for Vader as possible, allowing him to channel immense dark side power, but never get too strong. In doing so, Palpatine made sure the suit was extremely electrically conductive and ensured that Vader’s critical life support systems would pass through his arms, putting them at severe risk of shorting out and killing Vader if he used force lightning.
Palpatine did this so that if his apprentice ever attempted to overthrow him, there was a glaring weakness to stop him…
As a result, Vader Couldn’t use force lightning without the risk of getting himself killed..