Testing a UV Light Meter

It is not necessary to use a UV light meter for platinum/palladium printing. After all, generations of printers have made excellent prints without one. But when I saw that lightmeasure.com is selling reasonably priced UV light meters I couldn’t resist buying one. I bought a PPM-2 meter with a short wavelength sensor.

I bought it in the hope that I could answer the following questions:

  1. How long does it take my UV flourescent tube array to warm up and reach stable output?
  2. How much UV light is blocked by the glass in my vacuum frame?
  3. Is there significant fall-off of UV intensity towards the edge of my vacuum frame? In other words, what is the ‘safe’ area for printing?

I was very pleased to discover that this light meter has answered all of these questions for me. The meter worked well and was very easy to set up and use. I particularly like the flat cable that allows the sensor to be tucked under my vacuum frame’s glass.

Answering the first question was easy. When cold, the tubes take 2-3 minutes to reach stable output, but once warm they reach stable output after less than 20 seconds. The second question was also easy. The glass in my vacuum frame passes through about 85% of the UV that hits it.

After quite a lot of measurement and calculations in Microsoft Excel, I was able to answer the third question too. The ‘safe’ area under my UV tubes is approximately 30cm x 60cm. Outside this area the fall-off approaches 1/3 of a stop, which is more than I am comfortable with. This is plenty enough for an 11″x14″print. Here is a chart that shows the UV intensity under my array of UV fluorescent tubes.

UV Coverage – 46x78cm Array of BL Flourescent Tubes (288W)
UV Coverage – 46x78cm Array of BL Flourescent Tubes (288W)

I’m not yet sure how useful these data are for other printers. The type of lights, their electronic ballasts, and the distance from the print are all factors to consider. Hopefully it’s interesting nonetheless.

Originally published: August 22, 2015

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