Ultraviolet

Ultraviolet (or UV light) was light of a wavelength shorter than visible light. Though some creatures like humans were unable to see it, others, like the V'orrn, could. (PROSE: Placebo Effect)

Some deep sea creatures were susceptible to ultraviolet light. The Myrka could be stunned or killed by ultraviolet light. (TV: Warriors of the Deep) The Saturnyns were repelled by ultraviolet light and killed in high amounts. (TV: The Vampires of Venice)

Ultraviolet light could also be dangerous to other lifeforms. The Ice Warriors called ultraviolet light the "Red Dawn", which the Fifth Doctor described as "dying from sunburn". In the 21st century, Earth's thicker layered atmosphere compared to Mars at the same time could filter the ultraviolet rays, protecting life there. (AUDIO: Red Dawn) Millenia before, the ultraviolet light on Mars increased to fatal levels after the Key to Time was removed from the planet, causing climatic changes. (AUDIO: The Key 2 Time - The Judgement of Isskar)

On Solos, ultraviolet rays reacted with a nitrogen isotope in the soil to produce a mist toxic to humans. (TV: The Mutants)