...Perhaps a definitive
wiki article is in order?
Once the
wiki comes back in its entirety, remind me. Here's my thoughts on long-life lamps. Since you lose
intensity, you'll more than likely be running them higher, so the
halogen cycle not working isn't really an issue. Also, I believe we've determined in the
Preheating Conventionals thread, that that the
halogen cycle only stops works at a very low percentage, like 25% or something.
In this
post, Gafftaper states:
This cycle doesn't work when lamps are dimmed, so it's good idea to run your Halogen lamps on high for a few minutes at the end of the show. So that the process can kick in and the tungsten molecules can be relocated back to the filament.
But he is citing Richard Cadena's
book,
Automated Lighting. There are many errors in this
book, so now you've got me on a quest to prove them both wrong...
On this
site, the author states:
In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".
Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton or xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency.
In this
post, (same thread as cited above), gafftaper states:
-A tungsten filament can reach temperatures over 3600 degrees Fahrenheit and can produce temperatures on the envelope over 1600 degrees F. (DON'T TOUCH!)
While I can't find an exact
envelope temperature, according to this
site, the max.
pinch seal protection temperature of an HPL575/115V lamp is
Philips P3 technology, Max 500 degree C [932 °F] pinch temperature.
No pinch protection, Max 350 degree C [662 °F] pinch protection.
So one could surmise the
halogen cycle may stop working below ≈50%. I can do more investigation if you insist, but ship can probably quote the figures off the top of his head without any research.
Mr. Cadena's and gafftaper's statement about running the lamps to full (which usually happens during the
curtain call anyway) can counteract the loss of the cycle during the show seems valid.
charcoaldabs, did that answer your question? You owe me 01:41:00.00 (
SMPTE notation) of my life back!