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. (EDA: Placebo Effect)

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

Ultraviolet light could also be dangerous to other lifeforms, sometimes causing cancer. The Ice Warriors referred to the ultravolet light as the "Red Dawn". (BFA: Red Dawn) It increased to fatal levels after the Key to Time was removed from the planet, causing climatic changes. (NA: The Key 2 Time - The Judgement of Isskar)