Question: Difference CFL and Tube light?

Joris is asking a question about spectral-workbench
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by Joris | April 30, 2016 19:31 | #13056

What I want to do or know

In the advanced calibration video, it is emphasized that a CFL is needed for calibration, and that a regular old "straight & long" tube light is a lesser choice. At first glance the blue peaks appear to be smaller or more spread out.

I always thought they are essentially the same, just in a different form factor. Can someone enlighten (all pun intended) me as to the difference, both in a calibration sense and in the physics/chemistry root cause?


All fluorescent lamps produce visible light when UV light from excited mercury gas excites phosphors coating the inside of the lamp. Most compact fluorescent lamps use the same phosphors, but there are a few different combinations of phosphors used in tube fluorescent lamps. This Wikipedia article has spectral intensity graphs for several types of lamps.

Most of the different lamp types produce peaks at about 435 nm and 546 nm because those are not emitted from phosphors but from the mercury gas which is in every type of lamp. Any of those lamps can be used to calibrate a spectrometer, but those two peaks in a CFL are much more distinct so recognizing them and lining them up is easier.


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@matej has been scanning and comparing both types in this note:

Chris, do you recall when one of us posted a set of a CFL and a long-tube type (pure mercury) bulb in Spectral Workbench some time ago? I think we used it to try to figure out which of the two green peaks in a CFL was actually a mercury peak. I can't seem to find where we did that...

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I don't think I ever posted a tube fluorescent spectrum. But that's a good idea because those Wikipedia spectra of tube lamps don't all have the second peak near 544 nm. That would be consistent with the 544 nm peak being from something other than mercury (since mercury is present in all the lamps).

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Ah, here it is -- not a great scan, but done on the same instrument in a short span of time:

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This is very helpful guys. Thanks

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