Adapted from Wookiepedia.

Designed to be equally effective in both combat and ceremony, the lightsaber is inextricably synonymous with the Jedi Order’s values to uphold peace and justice throughout the Galaxy. This perception has always endured, despite the many conflicts between the Jedi and the Sith, who also used the lightsaber extensively.

A lightsaber consists of a blade of pure plasma emitted from the hilt and suspended in a force containment field. The field contained the immense heat of the plasma, protecting the wielder, and allowed the blade to keep its shape.  The hilt was almost always self-fabricated by the wielder to match his or her specific needs, preferences and style. Due to the weightlessness of plasma and the strong gyroscopic effect generated by it, lightsabers required a great deal of strength and dexterity to wield, and it was extremely difficult—and dangerous—for the untrained to attempt using. However, in the hands of an expert of the Force, the lightsaber was a weapon to be greatly respected and feared. To wield a lightsaber was to demonstrate incredible skill and confidence, as well as masterful dexterity and attunement to the Force.

Ironically, the Sith Empire was ultimately responsible for the advancement of lightsabers, replacing the original belt-mounted power pack with a smaller power cell within the hilt. An internal superconductor was introduced, which transferred the returning looped energy from the negative-charged flux aperture back into an internal power cell. With this modification, the power cell would only expend power when the energy loop was broken, such as when the lightsaber cut something, solving the need for a large, separate power supply.

With the Great Jedi Purge, lightsabers were outlawed. To further hinder surviving Jedi, Palpatine had many of the sites where Jedi traditionally collected lightsaber crystals razed or quarantined, and placed strict sanctions on any crystals available on the market that could be used on such, such as Corusca gems.  Jedi were forced to refrain from drawing their lightsabers during this era, as openly displaying their traditional weapon would only draw attention.  Ultimately, the only individuals permitted to wield lightsabers were Palpatine’s own Dark side servants, such as Darth Vader or his Shadow guardsman, to name a few.   As the widespread outlawing of these weapons made an already rare artifacts now almost impossible to find save in the hands of surviving Jedi, Jedi hunters would often collect the weapons as proof of kill, either turning them over to the Empire or keeping them as trophies.

Traditionally, the Jedi favored Blue blades and the Sith Red, though there where exceptions.  Most notably was Mace Windu’s amethyst blade.  However, years later when Luke Skywalker set about constructing his lightsaber, he was forced to use a synth-crystal for his weapon, as he lacked any knowledge of the sites where Jedi traditionally gathered crystals, most of which had been destroyed anyway. The resulting crystal possessed a green coloration, due to both the crystal’s composition and Skywalker’s meditations upon it during its formation.