Light is electromagnetic radiation at frequencies that were sensed by the humanoid eye. Occasionally, the term "light" was used to refer to electromagnetic radiation in general. A quantitative unit of light is the photon, with the unit of measure known as the electronvolt. Photosensitivity was a sensitivity to light.
Three dim lights seen by Commander Trip Tucker in the catacombs beneath the Vulcan monastery at P'Jem assisted the landing party from Enterprise NX-01 in their escape in June of 2151. These lights were the holes of the eyes and the mouth of a large wall sculpture in the atrium of the monastery. (ENT: "The Andorian Incident")
In 2151, Sub-commander T'Pol suggested to land the shuttlepod near one of the two poles on Archer's Comet as the surface ice would be more stable out of direct sunlight. Later, after Shuttlepod 1 crashed through the ice surface several meters down, the surface ice was recrystallizing after the comet went out of direct sunlight. (ENT: "Breaking the Ice")