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B Question about light emissions of fluorescent bulbs

  1. Dec 25, 2016 #1
    So today I was in one of the rooms in the gym where they have 4 fluorescent lights shining. 2 of them where clearly low on life/power and they were barely glowing, the glow was this very faint pink color.

    So my friends asked me why I thought they were glowing pink. On the spot I thought of some random bullshit and said because the lights were obviously very low on power/energy they could only emit light from the shortest wavelength, which is red.

    I want to know how accurate my hypothesis really is. And if you guys have any ideas as to why the lights had a faint pink glow.

    I have a newfound interest in science, so little things like this happen to be extremely interesting to me lol.
  2. jcsd
  3. Dec 25, 2016 #2
    I had a feeling it's loss of mercury... but I checked by putting "Why old fluorescent lights pink" in google search ....many hits the best being this ... https://en.wikipedia.org/wiki/Fluorescent_lamp ..

    The new lights contain a small amount of mercury inside a tube with low pressure argon , the mercury vapour makes the lamps work efficiently producing UV which the white phosphor coating on the glass turns into visible light ... over time the mercury gets absorbed by the glass and others components of the lamp ... when the mercury is mostly gone the argon base gas takes over as the primary discharge causing the light to change to pink
  4. Dec 25, 2016 #3

    Paul Colby

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    Florescent bulbs usually use a vacuum discharge to generate ultra violet (UV) radiation which is a shorter (higher energy photon) than is visible to the human eye. The UV then hits a specially designed phosphor the typically whitish dusty material on the inside of the bulb. The color of the light is determined by the choice of this phosphor. In old CRT TVs Red Blue and Green phosphors were used to generate the different color pixels. Interestingly, modern "white light" LEDs are really UV LEDs that illuminate white phosphors to make the light you see. This is how car headlights work and the canned lighting in my house. It's a very efficient way to generate light. The spectrum (color) of the light is determined by the phosphor mix used.
  5. Dec 25, 2016 #4


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    The two posts above give the impression that these sources ONLY generate UV light. They do not.

    These Hg sources generate a bunch of spectral lines, many of them within the visible range, in addition to the UV spectrum. The coating on these lamps are there to capture the invisible UV light and convert it to the visible part, thus generating even more light that we can see.

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