Kimiyo Hoshi is a distinct character from the DC villain of the same name. She has, however, crossed paths with the villainous Doctor Light on several occasions. During their first encounter (Suicide Squad #52 (April 1991) ) they briefly ended up in each other's body; a description of their most recent meeting (Green Arrow vol. 3, #54 (November 2005)) appears below.
As the Crisis continued, Hoshi's fascination with the phenomenon grew into an obsession while the men grew concerned for their safety. Disgusted by their mounting fear, Hoshi arrogantly insulted them and ordered an evacuation, leaving her to study the Crisis alone through her telescope.
Meanwhile, the Monitor, a being linked with all positive matter, senses his enemy, the Anti-Monitor, absorbing yet another positive-matter Earth with his antimatter cloud. In order to tip the scales for the heroes of the positive universe, the Monitor activates one last warrior.
He sends a devastating beam of energy from the star Vega to Earth, which strikes the observing Hoshi, leaving massive destruction in its wake. Granted the power of photonics and the name Doctor Light, Hoshi is assigned by the Monitor to guard one of the vibrational forks needed to save the Earth. Teen Titans member Starfire and Outsiders member Halo set out to destroy the machine. Since Doctor Light can't speak to them in English, she resorts to blasting them away from the machine. Superman is the first to communicate with her, given his knowledge of most of Earth's languages.
Once the Earth's heroes and villains are brought aboard the Monitor's satellite, the Japanese-speaking Katana takes over as Kimiyo's translator.
Doctor Light, granted the ability to understand English, accompanies several heroes to the anti-matter universe to confront the Anti-Monitor. She and Superman soon discover the machines that the villain has deployed to destroy the remaining Earths. The Anti-Monitor ambushes the Man of Steel; Doctor Light defends Superman as best she can. Supergirl arrives, and sacrifices her life, allowing Doctor Light to carry the unconscious Superman to safety.
Seeing Supergirl's sacrifice makes Doctor Light realize how selfish she has been, and she resolves to change.
When Harbinger summons her to fight in the final battle, Doctor Light is ready. As the other heroes barrage the Anti-Monitor, she absorbs the energy of a gigantic star that he is using as a power source. Scoring the first fall of the Anti-Monitor during that battle, she blasts a gaping hole through him.
In the post-Crisis continuity, Supergirl was written out of existence, so it is explained that Doctor Light was inspired by the other heroes.
She is potentially one of the most powerful superheroines in the DC Universe, but she has not tapped into the heightened levels of power she used during the Crisis. (Although few remember those events, Doctor Light is one of the few who do, seeing as how she once mentioned in Showcase '96 #9 (October 1996) that she's faced "Anti-Matter Gods".)
Doctor Light has joined the Justice League a few times over the years, most notably as a member of Justice League Europe during the latter half of its incarnation. (She was also a one-time ally of the Outsiders and was briefly part of an incarnation of the Doom Patrol.) During her time on the Justice League Europe, she believed that her anti-social attitude during the Crisis was due to the food she regularly ate, after Power Girl is diagnosed with a similar condition. However, it is revealed that her behavior in Crisis was, in fact, her genuine behavior. While a member of the Justice League, Doctor Light formed significant friendships with The Flash (Wally West) and Power Girl. There is a protracted period of animosity with the member of the Global Guardians known as Rising Sun. His romantic endeavours win out and the two enter into a relationship
In Green Arrow vol. 3, #54 (November 2005), following his recovery from the mind-wipe he suffered at the hands of the Justice League, Arthur Light, the villainous male Doctor Light attacked Doctor Hoshi and drained her of her powers.
It appeared that her de-powerment was temporary; in Infinite Crisis #5 (February 2006) she used her powers to aid in the evacuation of Tokyo, Japan. In that same issue she was warned by Bart Allen, in the costume of the Silver Age Flash, of the escape of an enraged Superboy-Prime. She was later seen in Infinite Crisis #7 (April 2006) battling the evil Doctor Light.
However, an article discussing the destruction of Star City (and, by extension, Kimiyo's depowerment) appeared at the 52 website, which is designed to complement the weekly comic series. The article places a date on the city's destruction, which was depicted in the final 2 Pre-OYL Green Arrow arcs, specifying that the event took place on May 15th. Problematically, this dating places the story after the events depicted in Infinite Crisis.
Given this dating, Kimoyo's depowerment took place during the events of 52 - Week 2 which, given Kimiyo and Green Arrow's appearances at the end of 52 - Week 1, would appear to make sense, although it in turn makes nonsense of information contained in Green Arrow vol. 3, #54, where it is revealed that Kimiyo has not used her powers for two years.
The story arc also concludes with Green Arrow experiencing a strange multiplying effect that places the story during Infinite Crisis, not two weeks after the event's conclusion. (Several other characters in the DCU experienced this effect in the issue of their titles that immediately preceded the OYL jump.)
Kimiyo Hoshi appeared in costume in 52 Week 35, alongside various other heroes. All are assisting the injured victims of Lex Luthor, who had caused a rain of 'supermen' by deactivating their powers. She is also shown in 52 Week 50, in the climactic battle of World War III.
Dr. Light appears in World War III: United We Stand, the fourth issue of the World War III mini-series that coincided with 52 Week 50. She is one of the first wave of heroes who confront (and are taken down by) Black Adam. He grasps her neck with such force that she instantly blacks out; he throws her aside.
Geoff Johns has revealed on his message board that he is working on storylines involving Doctor Light.
Oracle invites Kimiyo to join the Birds of Prey (issue #100), but she was not selected to take part in the first mission. She does, however, appear in Birds of Prey #113 (January 2008), assisting Oracle by scanning the electromagnetic spectrum for any evidence that might lead her to the parties responsible for an influx of hi-tech weaponry being smuggled into Metropolis. She is, however, unable to locate any such evidence.
Gail Simone has confirmed in a chat on comicbloc.com that Kimiyo's children have not been retconted out of existence by the recent changes to DC continuity (that resulted from Superboy-Prime tampering with reality during Infinite Crisis).