Re: Season misconceptions in newspaper

[Bernard Cleyet <anngeorg@PACBELL.NET>]

"Supposing that Bernard paid $4.20 for his Quartzline 500 W bulb,
that would represent 95.2 lumen.hours per watt.cent.

The projector bulb, on account of its reduced life and increased cost
is not a candidate for general purpose illumination on this account,
at < 1 lumen.hour per watt.cent  and would be replaced in a modern
 design by a halogen incandescent or xenon strobe  source.

Brian Whatcott    Altus"


I took the only comparable pair available (old table, which gives nearly the extremen.), so BW is quite correct in faulting the comparison.

Until the advent of concentrated arc lamps and then inexpensive LASERs, Std. lab lamps were W ribbon filaments operating at 6 => 14 V.  The 30A/T20/4 at 30A has so long a life that it's not given in that table  It's a 60 cd; T (color) 2300 K; 225 W lamp.  If "over voltage" to 640 W; 700 cd; 3000 K, it still has a long life.  However, another table gives its life as 300 hr. at 3100 and 100 at 3200 (color temp.)

A tungsten table gives the evaporation rate of W as a function of temp. (deg. Kelvin; color temp. and thermo. temp. differ by ~ 50 to 110 deg. in this range).  If one assumes that life is proportional to the rate, I find the life is exponential with one order for ~ every 200 deg.  Therefore, at 3,000 deg. the life should be ~ 1k hr. and at 2300 ~ > 100 k hr.  Long before this, the envelop will be darkened.

bc

p.s. I think it was I. Langmuir's * great invention to add an inert gas to reduce the evaporation rate.  Again a trade off: much longer life, but reduced efficiency due to the thermal conductivity.


*  Yes (1913), and I discover that H. Becquerel (1867!) was the inventor of the fluorescent lamp!





Brian Whatcott wrote:

> At 01:18 AM 6/22/2003 -0500, John Clements, you wrote:
>
>
>
> > /snip/ they were implying that the 60W halogen bulb would save
> > money because it was more efficient than a regular 60W light bulb.
>
>  If a hot filament is surrounded by an inert atmosphere
> it loses tungsten to its surroundings. In a local region of the filament,
> the deltaR leads to a 2*(deltaV), providing increased
> energy dissipation in that region; a recipe for local filament failure.
> One limits the filament temperature to keep its life at acceptable
>  levels in the  700-2000 hours range.
>
> Some commercial examples of halogen lamps have provided
> consumers with discouraging service.
> In particular, there was a rash of free standing tall halogen lamps
> ("lumieres")which provided a source of bad smells if insects flew
>  into their hot surface, which started house fires if curtain
> drapes blew onto them,and which oxidized their bulb connectors
> at the high temperature in effect at the small contact areas of
>  base metal provided  (in contrast to the generous contact
> surfaces provided in auto headlamp usage.)
>
> /snip/ I have also seen efficiency claims being made for other halogen bulbs
>
>
> > which have similar light output compared to standard bulbs of the same
> > wattage.
>
> /snip/
>
>
>
> > John M. Clement
> > Houston, TX
> >
> > Bernard Cleyet <anngeorg@PACBELL.NET> said earlier:
> > /snip/
> >
> >
> > > From an old table (< '68 ca.) two comparable lamps:
> > >
> > > Both std. and Iodine cycle  (quartzline) 500 W operated at a color
> > > Temp. of 3200.    /snip/
> > > They both emit ~ 10K Lumens; the iodine has a life of  2,000
> > > hr..,  the std (CZX projection) only 25 hr.
>
> /snip/
>
> I took a pack of GE soft white incandescents off the shelf:
> the claim is
> Light Output: 1690 lumen
> "Energy Used:"   (Power)   = 100 watts
> Life: 750 hours
>
> A rational  lamp selection parameter would be
>  lumen.hours per watt.cent (of first cost)
>
> If the unit cost were $1.50, the parameter would give
>  84.5  lumen.hours per watt.cent
>
> Supposing that Bernard paid $4.20 for his Quartzline 500 W bulb,
> that would represent 95.2 lumen.hours per watt.cent.
>
> The projector bulb, on account of its reduced life and increased cost
> is not a candidate for general purpose illumination on this account,
> at < 1 lumen.hour per watt.cent  and would be replaced in a modern
>  design by a halogen incandescent or xenon strobe  source.
>
> Brian Whatcott    Altus