A while back I wrote that the man at Voltarc (whose name I have in my
notes, for what that's worth, but who had been technical director & did
seem to me to know EVERYTHING about phospors & nanometers, for what
that's worth) explained that their AQA bulbs (now in use at ICP) peaked at
415 nm, which happened to be the PEAK sensitivity (he said) of platinum,
while dichromates generally (with some variations by
chemistry & colloid) peak at 360, but that tests showed either bulb
worked EQUALLY well for either medium, the overlaps apparently equalizing
each other.
As I then added from my own experience, times are short enough
with PROPER construction of the UV light table (I had to INCREASE the
paper distance on mine to get times long enough for control with gum --
which had been less than a minute) to make any possible theoretical or
actual difference between the nominal 415 and nominal 360 not something you
need to worry about. (Then Adam Kimball weighs in claiming negatives at
density 2.2 (!) but, I repeat, own experience shows, and the Voltarc fella
advises, that times are COMPARABLE if not IDENTICAL with the two bulbs.
There's also the fact that one might decide to change media -- to or from
platinum. Etc.)
Again, as I said in my post on the
subject about a month ago, there seems no reason not to get the
more easily available and INEXPENSIVE bulb, that is, the plain BL bulb.
What is actually more important than an attempt to differentiate
between nominal 415 and nominal 360 is to
get all your bulbs at the same time and with a brand name (Sylvania,
Phillips, GE, whatever). That is, if possible, avoid bulbs just
marked "BL." My neighbor bought a set of six no-name bulbs on Canal street,
which proved to be
some 20% slower than mine in the same fixture (maybe an inferior phosphor).
Yes, we tested them.
> Which raises another point evident from some recent postings: why use
> "Black Light" tubes (by which, I assume, is meant those with black glass
> envelopes to filter out all the visible radiation)? Unless BL tubes are
> much cheaper, it seems a pity to absorb all those useful photons.
Mike, the common labelling in the States is "BL" for black light, by
which is meant ultraviolet light. The ones with the expensive glass to
cut out all other wavelengths (the latest I've seen have a dark blue look to
the glass when the light is off) have the designation "BLB," which stands
for (I'm told) "Black Light Blue." These bulbs seem to be sold
for places like discos (maybe there's some scientific use as well),
to give an eerie glow to your white sneakers on the dance floor.
It's possible of course that labelling in the UK is different (you even
spell funny, like "colour" & "glamour"!) but I have seen enough students
spend $30 per bulb for BLB instead of $12 per bulb for BL (I told them &
it's in my "source" sheet," but they weren't paying attention) and have
hand-held
them through the remediation -- plus my own use of BL over a 15 year
stretch-- to say flatly, "when on Canal Street, buy BL." (They emit a
palish pink or baby blue light when lit, depending, I'm told, on the
phosphor.)
As for the color of the visible light, permit me to add something that
occurred to me. At ICP, the present bulbs are, as I said, the AQA bulbs at
(Voltarc says) 415 nanometers. They emit a rather lethal-looking red
light. The previous bulbs were the BLB, about which I at the time
forbore to comment, but they were installed in a cabinet below eye level
and so not as noticeable. With the new conspicuous and conspicuously evil-
looking red glow, we got a sudden (I thought) rather hysterical, unworkable
and impractical system for a series of precautions to not
look at the light. This was, I repeat, for the bulbs at 415nm, actually
closer to the visible spectrum, hence presumably somewhat LESS
dangerous than the prior ones at 360!
What I figured was that the greater visibility and more visible brighter
LOOKING light, had a greater PSYCHOLOGICAL effect.
In any event, I wouldn't look at any of
these lights, or a tungsten either, any more than I could
help, with or without the AWFUL WARNINGS from people
who go sunbathing, smoke, and put their hands in the DEKTOL!
Finally, I understand from a couple of sources that there exist HIGH
INTENSITY blacklight flourescent bulbs, rather new on the market, which
require, for a 24-inch bulb, a 40 watt ballast, but that these are (or
were) quite expensive.
I also mentioned in my previous post that GE told me
they had a new
digital ballast, made in conjunction with Motorola, which gets installed
by a thumb plug (like your telephone
or keyboard). This, the man pointed out means, first, there's less
electrical wiring to do in configuring the
system,and, more important, the system will generate LESS HEAT. (Heat
problems in UV systems are from the ballast far more than the bulbs).
GE promised to send me data on the digital ballast, but
didn't and I let the matter slide, having more urgent hanging details
to fret over, but someone starting from scratch might call the GE
800 number and track down that info.
(I'm very tempted to note that I can't help wondering if you guys have
trouble registering this kind of information from a woman, but I know
that couldn't
possibly be the case so I won't. I think more probably my lengthy last
post on all this was eaten by my evil service provider.)
Cheers,
Judy