[Filthy]

I am using a home built light table/box with one 500w halogen worklight. It works great and my exposure time is a perfect 11:30 (excruciatingly slow for some, fine by me for the $30 I invested in the whole set-up!).

I am finding though, that when I set-up a gang screen and have images away from the centre of the screen, I am not getting as good of an exposure due to the angle of the light coming off of the halogen toward the edges of the screen.

If I bought a second halogen and spread them out to get a more even exposure across the entire screen, would my exposure time be reduced? Would it be reduced by half if I double the light sources?

I know, the easiest would be to set it up and try it, but I thought maybe someone might have an idea.

Thanks.

R

 

[InkedApparel]

adding a second light may not be the best solution for your problem.....how far away from the screen is your light source ? maybe try moving the light source farther away from the screen so the light reaches all the way to the edges of the screen.

Inked

 

[Klamath]

How far away is your light from the screen? I moved my light farther away to give it more even coverage across the screen and transmit less heat to it.

I expose my DXP for 36 minutes, I have plenty of stuff to keep me busy during that time, it's not like I have to sit there and babysit it. This works great for me and gives me great results, but of course this wouldn't fit everyone's needs.

I also think a single point light source contributes to giving you sharp images.

 

[tsagain]

You might want to try putting four 1'x1' mirrors around your light at 45 degree angles. I've had mine set up this way forever. It won't really decrease your time that much but it does force the light out to the edges.

 

[Filthy]

When I was building my box/table, I had read somewhere in here to set the distance from the light either: the same as the diagonal distance across the screens you are using, or the length of the longest side of the screen - I can't remember which.

But at any rate, I wasn't able to get this exactly right (due to lack of carpentry skills) but I am pretty close. I use 20x24 screens so I am somewhere around 22-24'ish inches away from the light.

I am generally getting good results, but toward the outer edges of my screen, the emulsion is clearly not as exposed as the centre. Images wash out fine, but the emulsion is a little softer looking and has that water staining appearance that you get if it isn't totally exposed (know what I mean?). I have just started to need gang screens recently and I was slightly concerned that the images toward the edges of the screen may not stand up to longer runs if they weren't as exposed as the centre portions of the screen.

After I washed out one screen and dried it, I put it back on the light table for a minute and exposed the outer edges over the centre of the light to see if that did anything to firm up the emulsion. I have no idea whether this does anything or not - could this lock-in my emulsion though?

 

[Klamath]

Wow, that's even farther away than mine, mine is about 18". Have you tried just extending the time?

 

[Filthy]

I thought of that, but I am getting a perfect exposure right in the centre with my time right now. I don't want to mess that up.

For the $12 I spent on the worklight, I'd rather add a light and adjust my total time down.

I'll play around with it and see.

 

[PositiveDave]

Your exposure distance should be about the diagonal of your screen, as you might notice there is a diffenence between the edges & the centre if you get too close. Too far and your exposure time goes up - 2x the distance = 4x the time.
The ideal set up is a point source, adding another light can give you undercutting. http://www.t-shirtforums.com/t-shirt-articles/t108270.html
You can calculate the optimum exposure time by doing this: http://www.t-shirtforums.com/t-shirt-articles/t106506.html

 

[micromaui-closed]

you are right where I was 2 weeks ago- this is what I did. I added a second 500w next to the other. my screen is 13 inches away and I keep it on for 3:15. I had problems with even exposure for the one light and it took 12 minutes. you can try a little long exposure time- but dont go over 4 1/2 minutes unless you want to wash out screen forever. also make sure you put something black behind the screen touching the squeege side.
this all worked good for me. it took 10 screens to practice on and I'm almost out of emulsion remover...

 

[RichardGreaves]

Addressed in these posts
http://www.t-shirtforums.com/screen-printing/t112595.html#post659917

Dual Lamps
http://www.t-shirtforums.com/screen-printing/t109877.html#post643219