In article ,
jim rozen wrote:
In article , DoN. Nichols says...

Hmm ... are you sure that you weren't seeing ultraviolet coming
through the phosphors.

This is not possible - the major component of the mercury line is
at 254 nm, which is way too short to be passed by the glass tube.
Also the phosphors are completely opaque at those frequencies,

Hmm ... the phosphors are sufficiently scattered so *visible*
light goes through with little problem -- just hold a flashlight behind
one to prove this. I doubt that there is sufficient density in the
phosphor coating to block the UV when it is so sparse in the visible.

because the coatings are engineered to absorb all of the UV and
convert them into visible light. Any UV that gets past the
phosphor layer and absorbed by the glass will reduce the lamp's
efficiency.

O.K. But I still have my doubts. I guess that the UV lamps in
the same form factor as the standard fluorescents is quartz glass.

Lighting phosphors have very short persistence. Long persistence
phosphors imply a metastable trap state in the system - and those
tend to be likewise be pretty lossy.

O.K. Scope phosphors tend to be selected for long decay times.
The same for CRTs for terminals with green or amber displays, while TV
CRTs tend to have rather fast decays -- as needed because of the
frequent changes. Obviously, the white phosphor terminals are using TV
CRTs for economy purposes.

Probably what he was seeing was the response of the actual phosphor.

Perhaps, though I still suspect UV penetration, even if somewhat
attenuated by absorption in the (quite thin) glass walls.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---