Fluorescence occurs rapidly ($\approx 10^{-6}$ to $10^{-9}$ s) but phosphorescence is slow, and is therefore observable ($> 10^{-4}$ s). So, is it right to say that fluorescent lamps actually fluoresce when they actually do is to phosphoresce? Or am I wrong in saying that?


1 Answer 1


Fluorescent lamps do primarily work by fluorescence. According to this Wikipedia article:

"The inner surface of the lamp is coated with a fluorescent (and often slightly phosphorescent) coating..."

First off, an electric current excites the outer electrons of gas atoms (typically mercury) within the lamp to a higher energy state. When the atoms relax back to their stable state, UV light is emitted. This UV light is then absorbed by a fluorescent material coating the inside of the lamp, which in turn fluoresces in the visible region of the EM spectrum. Some confusion could arise here as this coating is called a phosphor, even though the type of luminescence is fluorescence, not phosphorescence.

The rate at which the luminescence occurs is not important because there is a continuous supply of electric current. If it were necessary to provide light for any significant period of time after the power source was removed, then some type of phosphorescence would be necessary due to it's much longer lifetime as compared to fluorescence, as you pointed out. However, this is clearly not a requirement for a standard fluorescent lamp.

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    $\begingroup$ I wonder if the phosphors are solely fluorescent. Fluorescence would happen within nanoseconds. A phosphorescence half-life of about 20 milliseconds would greatly help reduce the 120 Hz flicker of the fluorescent lamp. $\endgroup$
    – MaxW
    Commented Jan 4, 2018 at 17:22
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    $\begingroup$ @MaxW Your comment got me reading more about this and sure enough the phosphors used to coat the lamps can be slightly phosphorescent. Your point makes sense and I suspect it's a matter of cost that drives the use of fluorescent materials vs phosphorescent. That's my best guess anyway. $\endgroup$
    – airhuff
    Commented Jan 4, 2018 at 17:49
  • $\begingroup$ Ahh right! There's a continuous supply of energy that's why we can observe it. And the amount of outer electrons excited relates to the intensity of light emitted by the lamp that's why they can get pretty bright! $\endgroup$
    – Acnologia
    Commented Jan 12, 2018 at 9:24

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