# Screen Exposure confusing.



## JoeyR (Aug 28, 2009)

Im new to screen printing with a budget. So the majority of my equipment is homemade. like my exposure unit.

I have built a wood box, painted the inside white and placed 4 21 inch grow lights from Lowes ( Shop Utilitech 21" Plant Grow Light at Lowes.com ) and just regular picture frame glass on top.










The problem is that i have trouble washing out my screens after exposing, they're somewhat good but the lines aren't good, a lot of the time stuff washes out that i don't want to be washed out. So i had purchased a SAATIprint exposure calculator the 21 step guide.









Now i exposed the screen with the exposure calculator for 7 minutes. when i washed the screen i had got this.








Sorry for the blurr but it only shows 3 solid steps.

The exposure calculator directions say i need to be left with 7 solid steps. if you have less than 7 steps you need to multiply your exposure time by the stated time on the back like so.









Going by what the table says i should expose my screen for 20 minutes? Ive already been doing them for 7 and from what i read you really shouldn't need to expose your screens for more that 2 minutes?

This stage is turning out to be very frustrating for me, if anyone could help me it would be greatly appreciated!

Im bassically asking how can i fix exposure so i can expose my screens


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## Jsaladin (May 23, 2010)

I am not sure about your bulbs. I dont think you are putting out the right amount of UV. You need to buy unfiltered black light bulbs. I am sure someone on here has posted where to get them. I almost think you can buy them from Ryonet.


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## mrvixx (Jan 13, 2009)

If you could find 21 inch unfilteredblack lights (not the purple ones) you should replace with those


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## jsf (Aug 4, 2009)

I have the same exposure setup. I have used 20w household daylights in my previous years and burned my screens successfully within 5-6 minutes time.

Now with the same setup, I have changed my bulbs to blue ones and burn my screens successfully for 2-3 minutes time.


Here's my first, with the daylight bulbs...










with the new blue bulbs...


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## wonubee (Oct 2, 2007)

Expose for the 20 minutes and see what you get or get some unfiltered black lights and expose for 2 to 3 minutes or get a 500 watt halogen and expose for 12 to 17 minutes. The exposure calculator has been extremely accurate in my experience.


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## nuclear_j (Dec 9, 2009)

You need one of these kinds of bulbs, the unfiltered UV lights. I'm not sure if grow lights are the same as these:

Light Bulbs from Topbulb

but they do not have a 21" T8. I built my own exposure unit too and purchased the things to hold the bulbs in, they advertise them as under cabinet lights. I then ordered the 18" T8 shown here.

F15T8/BL - 15W T8 FLUORESCENT BLACKLIGHT (PHILIPS 13036-9, SYLVANIA 21623)

I just burned some screens today, and with the emulsion I use (S.E.X.) it took only 25 seconds and I still got some under burn. Maybe look at getting shorter bulb holders and put them in vertically instead of horizontally.

Good luck and happy hunting!


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## tgoeltz (Aug 7, 2007)

Some "picture frame glass" may actually block UV rays to protect photos. You may wish to try different glass. 

Perhaps you can slide the glass half off and see if the part of the screen not over the glass exposes better. (You would need to tape your exposure calculator to the screen).


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## PositiveDave (Dec 1, 2008)

Try it without the glass or increase exposure time to 20 mins.
Exposure is a culmulative amount of uv light, 365nm is the most active wavelength. If you have weaker lights and/or a filter in the way you will need a longer time to get the same amount of light as a 'real' bulb.


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## JoeyR (Aug 28, 2009)

nuclear_j said:


> You need one of these kinds of bulbs, the unfiltered UV lights. I'm not sure if grow lights are the same as these:
> 
> Light Bulbs from Topbulb
> 
> ...



I went to a Bulbman store in my area and bought new light bulbs, i showed them the ad your link sent me too and they gave me bulbs that had a tag on them saying

SLI LIGHTING
black light
F15T8/BL350

I put them in my light box and they look like this










If that looks right how long should i test the screen under exposure for?


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## InkedApparel (Mar 18, 2009)

I use 6 f20t12 24 inch blacklight bulbs and get a nice burn at 11 minutes....so try 9 - 12 minutes and see which works best.....

Inked


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