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Ultraviolet light

  1. Jan 26, 2006 #1
    i dont know if this is in the right forum, but anyway...why is it that it's nigh on impossible to focus on the edges of an ultraviolet lamp? is it just me? cos i just see a blur at the edges, and i wondered if there was a reason why. is it to do with uv light being at one end of the visible spectrum?
  2. jcsd
  3. Jan 29, 2006 #2

    Claude Bile

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    What you seeing is obviously not UV light at all, but light emitted at the higher end of the visible spectrum (blue and purple frequencies). The reason it appears blurry is because the light is being emitted by a plasma.

    On an aside note, I hope you are wearing some sort of eye protection when staring at these lamps.

  4. Jan 29, 2006 #3


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    IIRC, the eye is adapted to the red, yellow, green regions of the spectrum and not to blue and violet. The ability to focus depends on the index of refraction.

    There is an effect known as chromatic aberration - http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/aber2.html - which I believe is the phenomenon responsible for the inability to focus at blue/violet when the eye is adapted/optimized for lower frequencies (longer wavelength).

    See - http://hyperphysics.phy-astr.gsu.edu/hbase/vision/visioncon.html#c1

  5. Jan 30, 2006 #4
    If at all something was Ultra violet rays, we cannot see it anyway. So the fact that we can see it also makes it clear that it is not Ultra Violet rays.
    I have a general doubt. I am a undergrad student and hence has no much knowledge abt waves and optics. Anyway differant colors seen on differant materials heve always puzzled me since even my middle school. So my doubt has to be answered in a very explanatory way. The doubt is that what will happen if at all there exists something which reflect only lights from Ultra Violet frequency and not any light of any other frequency.
  6. Jan 30, 2006 #5

    Claude Bile

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    Optics for UV lasers reflect only UV light, this is accomplished by putting high reflection coatings on the mirrors, optimised at the desired wavelength. Such coatings are mostly transparent, however they display tinges of purple and blue because the reflection spectrum usually intrudes into the visible.

    Note that on any optical surface, roughly 4-5% (depending on refractive index) of all optical wavelengths will be reflected (unless it is coated by a high-reflective or anti-reflectiv dielectric stack, or some other reflection modifying coating), so nothing ever looks completely transparent.

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