The Photonic Lifeforms are a species made out of photonic, rather than chemical, structure. They are essentially similar to Starfleet's holograms, which are photonic-based simulations. As a result, this species consider holograms as real and chemical matter as artificial or illusory.
They made first contact with Federation technology in 2375, when a pair of Photonic Lifeform explorers detected the USS Voyager 's holodeck playing a retro-style science fiction simulation called The Adventures of Captain Proton. Mistaking the program for reality, the lifeforms assumed Human form and attempted to interact with the holographic characters, but ended up in war against the maniacal Dr. Chaotica. The holographic death ray and other forms of weaponry on the program – completely harmless for material life – were actually deadly to them, resulting in a war which was very real. As technical problems prevented the Voyager crew from shutting down the program and attempts to explain to the aliens that they were fighting a simulation were unsuccessful (the aliens replied that everything in the holodeck was very real as their sensor showed, and the biochemical life forms are the ones which are simulated) the Voyager 's Emergency Medical Hologram was sent to make contact with the aliens and convinced them to help Captain Proton defeat Chaotica.