Those Sith who turned away from the dark side of the Force and embraced the light were known as Light Sith, or light-sided Sith.
During the time of the Cold War, a faction of Sith who leaned towards the light emerged within the structure of the Sith Empire. The Dark Council selected the Sith Lord Cendence for the task of hunting down and eliminating any Sith deemed impure.
During this period, Sith apprentice Jaesa Willsaam received orders from her Master to locate these renegade Sith. Jaesa accomplished her objective, eliminating them all. Sometime later, she came across a Light Sith who was severely wounded. Before his death, he spoke of Cendence. Jaesa located Cendence, but after realizing that he was killing any Sith he wanted, she killed him. Caliqu, another Sith Lord, then offered Jaesa his position.
Centuries afterward, a Sith Lord by the name of Darth Gravid also reached the conclusion that unwavering devotion to the dark side would condemn the Sith of his time to the same destiny as their predecessors. He sought a new philosophy where the Sith would embrace the light side of the Force, fortifying themselves with compassion and love, similar to their Jedi counterparts. Confined within his Jaguada stronghold, Gravid dedicated himself to gathering centuries of Sith knowledge passed down from Master to apprentice since the era of Darth Bane, which included: holocrons, crystals, scrolls, tomes, amulets and all other manner of artifacts. He then proceeded to destroy these items, aiming to ensure that future generations of aspiring Sith remained committed to the path he had established.
Unfortunately, Darth Gean, Gravid's apprentice, did not share her Master's perspective. Appalled by the destruction of the Sith's treasures, she attacked Gravid with her bare hands. After a fierce struggle, she succeeded in killing him, abruptly ending his plans. Although many valuable artifacts and teachings were lost to the flames, including the highly sought-after technique of essence transfer, Gean managed to preserve enough material to instruct her own apprentice, ensuring the continuation of Darth Bane's original intentions: unwavering allegiance to the dark side.
Darth Plagueis later referenced the events of Darth Gravid's death when searching for the lost method of immortality. Similarly, Plagueis would engage in actions similar to Gravid's in spirit—he attempted to terminate the Rule of Two, only to be murdered by his apprentice, Darth Sidious, who believed that ending the rule went against the essence of the dark side.
If Jaesa Willsaam remains aligned with the light side, she seeks out the Light Sith with the intention of forming an alliance. Her initial attempts are unsuccessful because they are suspicious of her and attack, compelling Willsaam to defend herself with lethal force. Surviving as a Light Sith necessitates a significant degree of suspicion, a fact well-known to her master, and her initial approach lacked the necessary credibility. Subsequent attempts prove more successful.
It is possible for a player character who is a Sith Warrior or Sith Inquisitor to embody the principles of a Light Sith. In the Inquisitor's situation, their actions lead to the acquisition of the title Darth Imperius, as their light-sided deeds are perceived as pragmatic measures that ultimately benefit the Empire. Notably, if the player creates a level 70 Inquisitor to begin the game at the Knights of the Fallen Empire expansion, their Sith title will default to Imperius, even if the game assumes they consistently made dark-side choices in all other aspects.
Originally, within Star Wars: The Old Republic, all light side Sith characters encountered by the player throughout the game wielded lightsabers with purple blades. This was due to a gameplay mechanic that restricted the use of red-colored crystals to characters aligned with the dark side. However, this restriction has since been lifted.