Reference Book: Star Wars Saga Edition Jedi Academy Training Manual
See also: Lightsabers
A Bondar Crystal is used in the creation of the safest Lightsabers, given to younglings for basic weapon training in the Jedi Temple. Bondar Crystals create wholly nonlethal Lightsabers that merely shock the target and do not actually cut into it. Typically, Lightsabers with Bondar Crystals see use during sparring sessions between Padawans, as they allow the Jedi to actually strike the target with what would be a serious blow without permanent harm. Kathracite Crystals, on the other hand, produces a more traditional Lightsaber blade, albeit a weaker one that is less likely to cause serious harm in case of an accident.
By the time an adventuring Jedi begins their career, they have likely abandoned Training Lightsabers entirely and uses a full-strength Lightsaber, albeit not one of their own creation. Lightsabers with a Bondar Crystal or Kathracite Crystal usually appear in the hands of younglings, or are kept safely in reserve by the Jedi Temples and Academies for when new students come of age.