James,
Thanks for the input. I considered mercury vapor lamps, but I don't care for the discontinuous spectrum. The strong mercury line at 365.483nm is right at the sweet spot for UVA exposure applications, but it is very narrow. Metal-halide does not have as high a peak at 365nm, but has higher off peak intensity.
Here is an excellent article on exposure issues,
http://www.thegrendel.com/Shop/osc/grigar_article2.phpThe discussion comes from the screen printing direction, but applies equally well to all UV exposures.
One of the problems with the many DIY exposure boxes, is that the designers do not have the slightest notion of their exposure intensity which is very important. For example, Dupont has the following recommendations for Riston (in general):
peak wavelength: 350-380nm
>= 5mw/cm2 for >= 5 mil resolution
>= 10mw/cm2 for 3 to 4 mils
>= 20mw/cm2 for < 3 mils
exposure range: 35 mj/cm2 to 150 mj/cm2 (across different variants of Riston)
Since 1 mj = 1mw for 1 second, one should be able to expose any Riston variant in 15 seconds (15sec∗10mw=150mj/cm2) with a 10mw/cm2 intensity at the cure surface.
I decided to stop guessing about my exposure intensity and bought a UV radiometer. It is a UVAB meter for the range 280-400nm with NIST traceable calibration at 365 nm.
I have been using a Damar, 25w, blb, spiral, CFL in a parabolic shop light reflector. This bulb has peak emission at 352 nm. that falls off to ~ 0 at 300 nm and 400 nm. I thought this bulb had nice output: WRONG! The measurements across the bottom of the reflector, at 3" varied from 1.1mw/cm2 to 3.6 mw/cm2 (at the center). I found some data on a NEC blacklight T10 which is made in Japan and I think available in Australia: at the face, 4.82 mw/cm2, at 3", 0.96 mw/cm2, at 6", 0.55 mw/cm2. These data are consistent with my spiral blb.
I then measured the output from a plain old 20w 120v halogen under cabinet puck with its glass cover which said UV Filter-001. At 3" the reading was 22 mw/cm2 and with the glass cover taken off the reading was 25 mw/cm2. This was quite startling. Halogen bulbs generally have a bad reputation for producing UV. It also implies that all of the UV fluorescent DIY exposure boxes are inefficient designs. Moreover, I think when bulb manufacturers say "UV blocked" they really mean UVB, but do not say so. The percent reduction with the glass shield is about the same content of UVB as in the full UV spectrum for a halogen bulb.
I am awaiting delivery of my metal-halide unit which is pictured here,
http://www.championlighting.com/product.php?productid=9000100&cat=0&page=1Unfortunately, I will probably not be able to report an intensity that is greater than 40 mw/cm2. This is the maximum reading for my meter. Moral, read the specs carefully before buying...
Baxter
> Metal halide lamps produce relatively little UV, the halide salt vapors absorb it. A clear mercury vapor lamp produces much more, while the bare quartz arc tube from one is a very powerful UV emitter, the latter will produce large amounts of ozone.
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