Star Wars: What Do the Lightsaber Colours Mean?
The Star Wars Lightsaber Colours, Explained
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Red lightsabers are used by the Sith and other dark Jedi. According to "Star Wars: The Secrets of the Sith," red lightsabers are powered by synthetic crystals. Since dark Jedi can't form a connection with kyber crystals, their negative emotions would taint the crystals. This process, known as "bleeding," would result in a crystal with a red hue.