Hi John,
Generally, gas discharge tubes cannot be operated in parallel. They
need a high voltage to start, but settle down to a low voltage ca. 90
volts (I guess) once they are conducting. With ordinary inductor
ballasts I have seen two 20W short tubes, each with their own starter,
wired in series with a 40W ballast. This is for 240V. Maybe that would
work with a high frequency electronic ballast.
I chose to use a 500 watt floodlamp from the hardware store. The short
linear quartz halogen lamps give off a lot of near UV, which is what I
want for exposing Riston negative photoresist.
At a distance of about 45cm I have exposure times of 2 to 3 minutes.
This is a much narrower angle source of light than having a bunch of
fluorescent tubes only 10cm away, so for a given phototool and possible
distance from the phototool to the top and bottom of the Riston, I get a
much sharper image (shadow).
The only potential concern I can think of is heating of the phototool,
PCB and whatever means is used to hold them together. I have a fan
blowing on them to keep them cool.
There's no warm-up time for a QI light. Tubular fluorescent lamps are
likely to have some kind of warm-up time, making it difficult to predict
their light output unless they have just been running and are fully
warmed up. High pressure mercury vapor lamps have much longer warm-up
times, and so do the compact fluorescent lamps which are now widely
used. All these fluorescent lamps - tubular, 400W (or other wattage)
high pressure mercury vapor lamps, and compact fluorescent lamps - come
in "black light" versions which I think put out the ideal wavelength for
exposing Riston.
http://www2.dupont.com/Imaging_Materials/en_US/tech_info/datasheets/index.htmlI haven't looked at all the types, but the types I have looked at are
specified to respond best to 350 to 380nm light. This datasheet for a
400W high pressure mercury vapour fluorescent H500-BL:
http://www.eyelighting.com/tb/Mercury/MVR/EQS-N-52-78-69917.pdfshows most of the output at about 370nm.
However, I think their warm-up times are a problem.
QI lamps will vary their near UV output somewhat according to their
operating voltage, but unless the mains voltage varies widely, I would
be surprised if this variation was enough to cause trouble with Riston.
- Robin
http://www.firstpr.com.au/pcb-diy/