The lightsabers technically aren't deflecting anything. Rather, they're absorbing the energy and discharging it right back to its source.
Darth Vader can not use force lighting, because of his severed arms. Robotic hands can't summon the force lighting.
Mace Windu, with his lightsaber combat form Vaapad, could reflect the lightning back to its source with a "superconducting loop". It required tremendous effort on the reflector's part, however, as seen in Windu's battle with Palpatine; Windu was seemingly able to overcome Sidious's lightning.
A Jedi and Sith could deflect the lightning with a lightsaber, such as when Obi-Wan Kenobi blocked Dooku's lightning with his saber; a powerful Jedi Master such as Yoda was capable of deflecting the attack using Force deflection but only for a short while and with immense effort.
By the dark side, the move is electrcial and therefore can be blocked by metal though there are some skilled users such as the Dark Jedi, Galen Marek who can imbuede his lightsaber with the force lightning and Yoda who in Episode III- Revenge of the Sith, Blocked Count Dooku's force lightning.
While Darth Vader doesn't use Force Lightning in the Star Wars films, the power played a key role in his story in the comics. Despite being considered one of the strongest wielders of the Dark Side of the Force, Darth Vader never uses Force Lightning in any of the films.
While many Star Wars fans would consider Yoda and Palpatine to be almost perfect antitheses of one another, it seems that they share a strange connection through Yoda's usage of Force Lightning in The Last Jedi that is eerily similar to something Palpatine did just a few years prior–and that connection goes much deeper ...
Force lightning is a dark side ability used to torture, disfigure, and even kill one's victims.
Gray Jedi commonly demonstrated their skills with both Light and Dark side Force capabilities. For example, the capacity to construct a lightsaber from scratch, along with unique Force talents such as Force lightning.
1 Darth Sidious
As well as being a gifted bladesman Sidious' connection to the Dark Side is extremely powerful, granting Sidious the ability to conduct force lightning.
Legends Canon: Yes he has. What he used was a variant of force lightning called “Emerald Lightning” which is supposed to be similar to Plo Koon's “Electric Judgement”.
Over the decades, For lightning has become strongly associated with the Sith. Palpatine is particularly fond of this power, using it to most spectacular effect in Star Wars: The Rise of Skywalker.
Jedi Battlemaster Cin Drallig and Grand Master Yoda had knowledge and mastery of all seven forms, including Juyo, befitting Drallig's role as lightsaber combat instructor at the Jedi Temple and Yoda's reputation of having mastered all forms of lightsaber combat as did Anoon Bondara, another lightsaber instructor.
It's the intensity of reflected lightning and the channelling of such raw dark side power that are the catalysts for Palpatine's transformation. Perhaps the face that boils up to the surface is shaped by his dark side corruption, but the lightning is definitely the cause.”
Sidious, born Sheev Palpatine, was trained in the dark side of the Force by Darth Plagueis. Eventually, Sidious took on his own apprentice, Darth Maul, and killed his master.
While he never showed the ability to use Force lightning before, it's appearance here helps communicate Kylo Ren's shift in his allegiance, and it's presently the only canon instance of Kylo using such an ability.
Let's be honest - it's not as if Yoda is going to have forgotten about that time back on Coruscant where Palpatine nearly fried him with lightning, so the logical answer seems to be that he didn't want to distract Luke with anything such as "watch out for this, that and the other" - he reminds Luke that the Emperor is ...
Electric Judgment, also known as Emerald Lightning, was a light side Force technique used to spray electric bolts of variable intensity from the hands and fingers.
Without question, the most powerful Force ability present in Star Wars is the Thought Bomb. It is created through an ancient Sith ritual where the Sith combine their dark side powers. If done successfully, the Thought Bomb can destroy all Force-sensitive beings unfortunate enough to be within the radius of its blast.
The true Force-form of Darth Vader explains why he can't use Force Lightning. Conceived by the will of the Force itself, and with a midi-chlorian count so high it was greater than even Master Yoda's, Anakin Skywalker was the greatest Jedi Knight of his generation.
However, despite their strict adherence to the light side of the Force, several Jedi were known to use this power, as although it was considered a dark side ability, it was also a technique of telekinesis. Its use, however, was forbidden by the Jedi.