Distance from bulb to printing frame

I know it is here somewhere, but can't find it again.

I am getting everything ready to make the dive into carbon, and other types of printing. I am building my exposure box. What is the distance between the lights and the printing frame.

Necessary Info:
Using LEDs as the light source.

Building a drawer type vacuum frame so the distance will not be adjustable, unless I can figure out a way.

Thanks for the help.

I think it depends on the spacing between your bulbs and the type and size of the bulbs. I'm using fluorescent tubes with about 1/4 inch spacing between them and I find a tube-to-print distance of 1 1/2 inches is sufficient to avoid any hot spots. You may have to do some experimenting before you finalize the build.

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Originally Posted by Denny

I think it depends on the spacing between your bulbs and the type and size of the bulbs. I'm using fluorescent tubes with about 1/4 inch spacing between them and I find a tube-to-print distance of 1 1/2 inches is sufficient to avoid any hot spots. You may have to do some experimenting before you finalize the build.

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Good answer Denny.

I can do that. Now I just have to figure out how.

One more thing you might consider is determining the maximum area that your light source is capable of illuminating evenly. This will determine the maximum print size without falloff at the edges, and will vary with distance from bulb to print frame. If you're handy with a spreadsheet you can do some theoretical calculations to get you in the ballpark (maybe easier to calculate if you're building with fluorescent lamps), or you might just wait and test your final setup. Here's an example of a plot from an old light box that had 6 bulbs:
Attachment 183400

Quote:

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Originally Posted by Denny

One more thing you might consider is determining the maximum area that your light source is capable of illuminating evenly. This will determine the maximum print size without falloff at the edges, and will vary with distance from bulb to print frame. If you're handy with a spreadsheet you can do some theoretical calculations to get you in the ballpark (maybe easier to calculate if you're building with fluorescent lamps), or you might just wait and test your final setup. Here's an example of a plot from an old light box that had 6 bulbs:
Attachment 183400

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You can chart this with a light meter right?

Maybe possible with an incident meter, I've never tried.