Screen Printing Forum

Hi all,

This is sort of a theoretical question and I was after any input you might be willing to offer on it.

If I were to...

1. establish a baseline using an exposure calculator for proper exposure
2. at the same time take a UV light meter reading from the exposure unit itself

Could I use the light meter 3 months later to figure out the degradation in the bulb output and adjust the time accordingly?

This question of course assumes that the screen mesh count, mesh type, emulsion / film type, and exposure unit have not changed.

So for giggles if the output is measured at the exposure unit surface to be 100 uW/cm2 and the exposure calculator dials the appropriate exposure time at 3 minutes 30 seconds

Can I then use the number of seconds multiplied by the UV output as a total UV requirement for that particular emulsion / film?

In this case 210 seconds * 100 uW/cm2 = 21000 time units of exposure for this specific film and set of variables.

after 3 months if the bulb UV output has dropped to 87uW/cm2 couldn't the total time units be divided by the current output?

Again this is assuming the same screen mesh count, mesh type, emulsion / film type, and exposure unit.

so 21000 time units of exposure / 87uW/cm2 would push the exposure time to 4 minutes 2 seconds.

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OK thank you to anyone who took the time to read that!!!

1. Is the logic of this approach sound?
2. is there any value in this approach?
3. is anyone using this approach?

Thanks again,

Screenalicious

Interesting concept I know the SPTF has done test on exposure light distribution using a radiometer in different spots on your glass to see how the light is distributed.
So I dont see why your therory would not work. As long as you set your base line with a new lamp and clean reflector and you measure in the same place everytime you measure. Basically your trying to replicate a intergrator. As for value in this approach if it works you will be able to determine if your lamp has degraded and maybe to what point it has. Then you can compensate for the lamp degrading. Even if your math don"t work you know you need X amount of energy to expose a screen properly then you can add time to your exposure until you hit X. The other value to this is you can just do spot checks and track your lamp.
If I didn't have an intergrator on my exposur unit I would try this.
Good post let us know how it works for you.

This should work, but with light it always depends upon the exact wavelength that you are measuring. Emulsions tend to be sensitive to 365nm light, the main output line of a mercury halide, if you are measuring a different wavelength it could give a dodgy result.
A stouffer strip on the emulsion each week should be enough to keep your exposure on track?