Use the adjective ultraviolet to describe light with a wavelength that's less than visible light, but longer than x-rays. You can't see ultraviolet light.

You might hear people talk about ultraviolet light as UV radiation — it's the part of sunlight that can give you a sunburn if you're exposed to it for too long. In physics, this kind of electromagnetic radiation is defined by how long its waves are. The word itself, ultraviolet, refers to the fact that its wavelength is shorter than the violet end of the spectrum of visible light. The Latin prefix ultra means "beyond."

Definitions of ultraviolet
  1. adjective
    having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end
    ultraviolet radiation”
    “an ultraviolet lamp”
    invisible, unseeable
    impossible or nearly impossible to see; imperceptible by the eye
  2. noun
    radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays
    synonyms: UV, ultraviolet illumination, ultraviolet light, ultraviolet radiation
    see moresee less
    sun-ray, sunray
    a ray of artificial ultraviolet light from a sunray lamp
    type of:
    actinic radiation, actinic ray
    electromagnetic radiation that can produce photochemical reactions
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