Dimroom 'safe' lights?

[MattKing]

The swatch had an overall UV exposure to a bit higher than a Zone VIII print density, so is very sensitive to fog.

This part wasn't clear before. So you have already done a UV pre-exposure "flash" sufficient to create some density before you add the safelight exposure. Well done .

I am trying to understand this - you are pre-exposing this test strip to Zone VIII and THEN leaving it out in different light conditions? Why not just use unexposed paper?

:Niranjan

Most light sensitive processes don't respond in a purely linear fashion. They exhibit some threshold behaviors - exposures lower than a certain level result in no response, but when the cumulative exposure is above the threshold level the materials start building density.
If you are performing a safelight test, the fact that the safelight alone doesn't raise the exposure above the threshold level doesn't suffice. You need to test for safelight induced changes in behavior - whether the density created using an above-threshold UV exposure is changed by the addition of non-image bearing safelight exposure.

To be absolutely complete, an additional test should be added - a UV post-exposure "flash" also sufficient to create some density after you add the safelight exposure.

 

[MurrayMinchin]

Most light sensitive processes don't respond in a purely linear fashion. They exhibit some threshold behaviors - exposures lower than a certain level result in no response, but when the cumulative exposure is above the threshold level the materials start building density.
If you are performing a safelight test, the fact that the safelight alone doesn't raise the exposure above the threshold level doesn't suffice. You need to test for safelight induced changes in behavior - whether the density created using an above-threshold UV exposure is changed by the addition of non-image bearing safelight exposure.

Thanks, that's a way more word-smith, wordier, comp-ree-hen-syble description

I'll be dialling back the amount of 'safe' light, and the paper is face down for at least half the processing time, so should be okay.

Before getting serious I'll do this again with a Zone IX (plus a bit) print density, to see if everything is still good. I'm unfamiliar with salt printing, so don't want to accept fogged high values thinking that's the way they're supposed to look.

Will also give that Kodak test a closer read.

 

[nmp]

This part wasn't clear before. So you have already done a UV pre-exposure "flash" sufficient to create some density before you add the safelight exposure. Well done .


Most light sensitive processes don't respond in a purely linear fashion. They exhibit some threshold behaviors - exposures lower than a certain level result in no response, but when the cumulative exposure is above the threshold level the materials start building density.
If you are performing a safelight test, the fact that the safelight alone doesn't raise the exposure above the threshold level doesn't suffice. You need to test for safelight induced changes in behavior - whether the density created using an above-threshold UV exposure is changed by the addition of non-image bearing safelight exposure.

To be absolutely complete, an additional test should be added - a UV post-exposure "flash" also sufficient to create some density after you add the safelight exposure.

Thanks for the explanation. A little too complicated for me. I only did plain coated paper - half covered and half exposed under "safe" light for a period of time and then develop and see if you see any difference. Obviously, this only shows if there is going to be any fogging in the white areas of the print due to potential UV exposure. It does not say anything about how it affects the other areas, which might change the resposnse curve and the contrast itself because of the threshold phenomena - what I understand from above.

:Niranjan.