Been out of the office, so catching up on some reading....

I have found that the fluorescent black lights come in two styles.  One is a
whitish fluorescent tube which looks identical to a regular fluorescent
except for the markings that indicate it is a black light, the other is the
purple colored black light.  I bought a desk lamp and two black light tubes
to fit it and when I plugged it in, the conformal coating glowed, but
barely.  Nothing like the old light that broke.  I did some looking up
online (Wikipedia - http://en.wikipedia.org/wiki/Black_light) and discovered
that they are made in two ways.  The first (white) type is normal glass but
with only one phospor, and the second type (blue glass) has glass that is
known as "Wood's Glass".  This glass, according to Wiki is "
nickel-oxide-doped glass, which blocks almost all visible light above 400
nanometers."   I have know idea how when you buy a "black light" what type
you are getting, but when I got those blue colored lights, the coating
glowed great again.   I don't know why, as "black light" is technically UVA
light in the range of 320 nm to 400 nm, so they should theoretically be
equivalent regardless of the method used to attain it.  But it made a
difference, so maybe one thing to check is what type of bulbs you have in
the booths and the inspection rings.

Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
Sent: 13 June 2007 16:15
To: [log in to unmask]
Subject: [TN] Black light intensity meters

Good morning all,
I have two questions that relates to conformal coating practices.  We have
a situation internal where we conformal coat assemblies in booths outfitted
with black lights and the coating has a fluorescent dye marker (Humiseal
1B31).  Most booths have four 22W black light bulbs.  Our inspectors use a
circular magnifier outfitted with a circular black light bulb.  The latter
has a stronger output, possibly because the black light bulb is much closer
to the surface being inspected.  This is leading to inspectors finding
coating "defects" which cannot be seen with the black light illumination in
the coating booths.  So we have a running dispute between inspectors and
operators.

1.  Is there a meter that any of you would recommend by which we can measure
black light intensity at various distances?  I know there are a number of
them out on the market, but many are also of the variety that check the UV
output of high intensity devices such as UV imaging of solder masks. 

2.  What do your workmanship standards say regarding inspection under black
light?  Distance, magnification, intensity?

Thanks.

Doug Pauls
Rockwell Collins

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