Luma as Superman's Lover
Luma first appearance was in Action Comics #289, June 1962, titled: "Superman's Super-Courtship!"
After watching a romantic movie, Kara begins to feel bad for Superman not having a significant other and decides to become his personal cupid. She sets him up on a few dates with people like Helen of Troy and an adult version of Saturn Girl, she comes to the conclusion that he needs someone more like her. She then uses the Fortress of Solitude's computer to look through the known universe for an adult superheroine and finds Luma Lynai, the Superwoman of the faraway planet Staryl.
Clark and Luma hit it off. Unfortunately, when Luma comes to Earth they find that the yellow sun of Earth is deadly to her. Earth needs Superman too much for Clark to be willing to leave it, so he and Luma break up.
Kara realizes soon after that she shouldn't interfere with Clark's romantic life.
Little is known about Luma's powers other than that they appear to be very similar to Kryptonian powers.
Luma's power comes from the Orange Sun of her solar system.
Luma is weak to yellow star radiation. The yellow sun's light weakens her powers and causes her physical harm. It appears to be deadly in the same way that kryptonite is deadly to Superman.
JSA Classified #3: "Power Trip, Part III" (November 2005)
A grown up Supergirl with Luma's suit appears to Power Girl in a Psycho-Pirate 's illusion.
The Kingdom: Planet Krypton #1 (February 1999)
It is reveled that one of the "ghosts" seen in the empty "Planet Krypton" restaurant is in fact Luma Lynai.
Superman's Girl Friend Lois Lane #97: "The Three Super-Sirens!" (November 1969)
She appears in Superman's memories while he remembers long lost lovers.