Re: old UV tubes less contrast?

----- Original Message -----
From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, March 02, 2006 12:55 PM
Subject: Re: old UV tubes less contrast?

>
> If the bulbs are facing up, you might try dusting them. At
> least around here, a coating accumulates. It's also true
> that bulbs are *brighter* when quite new, tho that soon
> tapers off. And, as I recall, the rated life of the bulb
> is circa 9 to 12,000 hours, no?
>
> Plus, did you change anything in the vicinity? Reflection
> counts.
>
> J.
>
   I suspect the behavior of low pressure UV lamps is the
same as regular fluorescent lamps. Fluorescent lamps lose
brightness with age and also take longer to warm up to full
brightness. All of these lamps like to run hot and will
increase in brightness as they warm up. Room temperature can
also cause dim lamps if it is really cold. They also do not
like excessive heat which may be a problem when the lamp is
completely enclosed.
   The life of these lamps is longest when allowed to run
continuously.
   There is a pretty good primer on fluorescent lamps at:
http://www.thekrib.com/Lights/fluor-goldwasser.html Most
of this applies to BL and BLB type UV lamps which are
essentially fluorescent lamps without the internal phosphor
coating. BL and BLB lamps are the same except that BLB lamps
have a filter coating for removing visible light output.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com