The Light Gem is an honorable spirit who stands out from the rest of the gems along with Bubble, Memory, and Glow. What I mean is, this gem wishes not for Ceaira`s destruction. Light`s powers are to shoot beams of light or to illuminate the surrounding area. Her form is a white knight with long silver hair.
Light appears in Episode 17, after Marietta and Anastasia move to Reidenton, and she challanges Ceaira to a sword battle. It lasted a while, but Ceaira finally managed to gain the upper hand so she could win. Light surrenedered with honor, and allowed Ceaira to seal her back into a gem form. When summoned, the powers of light can be harnessed.