Photosensitivity
Photosensitivity was a medical condition in which a lifeform was sensitive to light.

After a symbiotic lifeform captured several members of the  crew in 2152, Doctor Phlox was able to determine that the creature was highly photosensitive, resulting in a security team using EM emitters to weaken the creature. ()

The sole biological difference between the otherwise identical prime universe Humans and mirror universe s was that the latter were highly sensitive to bright light. Being Terran,  had severe photosensitivity that was exacerbated by the prime universe's different light, and to mask such an ailment, he claimed it was the result of eye damage from destroying the  during the  to spare his crew a slow death on Qo'noS. He refused treatment, supposedly to maintain a reminder of the incident but in reality because he knew analysis of his eyes would reveal nothing wrong and thus expose him as an impostor. Ultimately, Lorca's true nature was only discovered when Michael Burnham saw  being dazzled by the 's super-mycelial reactor. () 

The neural parasites encountered by the  in 2267 were found to be extremely photosensitive. Visible and ultraviolet light were both fatal to the organisms. ()

In 2364, chromosomal damage was causing the Aldeans to be sensitive to light. ()

Due to having evolved on the dark side of their tidally locked homeworld Remus, Remans preferred darker environments and were easily blinded by lights. ()

In 2367, Susanna Leijten developed an extreme sensitivity to light during the early stages of her exposure to the Tarchannen III parasite. ()

The Night Aliens were an extremely photosensitive species. Native to  region of the Delta Quadrant, the species' physiology evolved to survive in complete darkness. When one of the species was being treated in the sickbay on board the , The Doctor needed to dim the lights in order to accommodate the needs of the alien. ()

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Medical conditions