# Question about UV light from my 1st grader **URL:** \ **Category:** Factual Questions\ **Created:** [February 20, 2017, 10:18pm UTC](https://boards.straightdope.com/t/question-about-uv-light-from-my-1st-grader/780356 "2017-02-20T22:18:15Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [February 21, 2017, 12:28pm UTC](https://boards.straightdope.com/t/question-about-uv-light-from-my-1st-grader/780356/21 "2017-02-21T12:28:39Z")
> [@whitetho](#): > > This topic has come up a few times before. The main reason we can’t see near ultraviolet is because the eye’s cornea blocks UV light. However, some early cornea replacements were transparent to UV light. The unimpressive findings were that UV just looks whitish-blue or whitish-violet. When my father had cataract surgery, I asked him about this, but he said the doctors told him that modern cornea replacements are now designed to block UV rays. White ??? Its seen as white ? Thats being its not “seeing” in any sensible way. Thats the same as “seeing” nuclear radiation using your eyes. I am sure the UV light could be seen in any focus, it was blasting through the retina and activating nerves and so on … not forming a picture. People lacking a lens (a condition known as aphakia) perceive ultraviolet light as whitish blue or whitish-violet That was the more interesting thing - that even the frequencies closest to blue are still only being seen as white flash. The people making artificial lenses for the human eye also ensure that the lens is a UV filter, as the UV A would otherwise damage the eye. So for both the reasons, that the UV A range is also seen as a white flash , not a picture, and that UV A is highly damaging to the retina, and causes sunburn to the skin, there is no real possibility that the UV light would be seen as if was blue light. Its seen as a damage occurring to the retina and not as a resolved picture . ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 21, 2017, 12:48pm UTC](https://boards.straightdope.com/t/question-about-uv-light-from-my-1st-grader/780356/22 "2017-02-21T12:48:31Z")
> [@Isilder](#): > > I am sure the UV light could be seen in any focus, it was blasting through the retina and activating nerves and so on … not forming a picture. > > … no real possibility that the UV light would be seen as if was blue light. Its seen as a damage occurring to the retina and not as a resolved picture . This is not correct. If a lens focuses in visible light, and is transparent to near-UV, it would work reasonably well in near-UV. It won’t be in perfect focus, because of chromatic aberration, but it would still form a picture. In my field (UV astronomy) we sometimes use lenses in UV. If we select a lens material that is transparent in UV (e.g. MgF2) and correct for chromatic aberration, it works fine. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [February 21, 2017, 1:12pm UTC](https://boards.straightdope.com/t/question-about-uv-light-from-my-1st-grader/780356/23 "2017-02-21T13:12:52Z")
Wouldn’t it depend on the translucence of the medium in the marker? If it were an opaque ink, it would appear black, since it would block the reflectance of the white paper beneath the mark. But if it were highly transparent ink, the white would come through unaffected by any of the invisible pigmentation in the ink. Shades of gray would then be the correct answer. Ink is a suspension of opaque particles in a transparent fluid. [Previous page](https://boards.straightdope.com/t/question-about-uv-light-from-my-1st-grader/780356.md?page=1)