Exposure Unit

[Dan K-J]

Ok guys I need advice,

I am building a printing press table with an exposure unit box built underneath the table.
I'm printing on to frames 20'' X 24'' (outside measurement) 17'' X 21'' (inside measurement).
For printing onto paper with 90T Mesh.
And using AZOCOL Z1 screen emulsion.

Everyone recommends to use the halogen security lights 2 X 500W
But the best distance between the lights and the glass/screens are around 1 metre away.

What tube lights would you recommend and the exact distance between the glass and the lights giving the exposure time.
I want to produce a compact box which just fits my screen sizes above.

Cheers,

[jonkeefe]

We tried 500W halogens for a while, they got crazy hot and made me nervous. Fire waiting to happen.

I've seen a few people report great success using "actinic" aquarium tubes. They're meant to stimulate coral growth. Apparently you can get burn times around 90 seconds with a bank of those suckers(!!).

My exposure unit came with plain old cool white tubes, and my exposure times range from 20 to 30 minutes, depending on mesh size and thickness of emulsion. I'd love to cut that 30 minutes down to 90 seconds, but I hate waste and I don't want to toss six good tubes.

This thread might give you some pointers about tube placement.

[Dan K-J]

I dont wont to go with the 500W halogens inside a box because of the heat. Plus my box is going to be quite minimal so perhaps I should try a bank of unfiltered UV fluorescent blacklight bulbs?
90 minutes is silly fast! Would be pretty cool to have that exposure time. I will try out my exposure time once the bulbs are in place. If its a bit of a wait for the exposure I alway get my inks and bits ready to kill time.

[Andymac]

in UV tube exposure, the strength and speed of your exposure is determined by the type of bulb.
it goes Super actinic > unfiltered blacklight > blacklight...and I guess some people get it to work with regular bulbs (!)
The other variable is proximity. UV tubes aren not that powerful, so the UV is only good up close. Too close, and it will burn hotspots along the length of the bulb, and undercut your image, especially if you have no vacuum blanket. Too far away and it will be slow. Correct even spacing, correct distance from the glass are all considerations.

[jonkeefe]

We bought our unit second-hand, I'm kinda wondering what bulbs were originally in it.

It's an AWT Pro-Light, though, so it probably comes out of the factory with cool whites