> >
> > Didn't we have this same discussion on the list a few months back?
> >
> > Roland
> >
> We have to differentiate between the total heat emitted and that absorbed by
>the
> envelope (quartz or glass).
>
> I thought that the discussion was about heat in the light unit, not
>temperature
> of the bulb. Feel free to correct me if I am wrong about this!
I believe the original discussion resulted because of the concern that
additional external heat could cause damage to plastic lenses.
>
> I do believe that halogen bulbs run hotter -- but, I suspect that it may be
> because the quartz enevelope is smaller and thus it is poorer at distributing
> heat via convection.
This also occurred to me. The bulbs are smaller so a lot more heat
probably reaches the envelope because of the inverse square
relationship; they have a tubular rather than a spherical shape which
may not dissipate heat as evenly; and perhaps the fact that the
envelopes are filled with halogen rather than being evacuated is a
factor (pure speculation here).
Dave Bean wasn't the only source of warnings about the danger of halogen
bulbs melting plastic lenses so I'm inclined to take the possibility
seriously. Perhaps the total heat dissipated is about the same but more
focussed. Regardless, it is noticeably higher.
Roland
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