LED Screen Printing Exposure Unit

List of Materials

• 1/4” plywood for box
• 1/8” plywood for “deck” to support LED strips
• Pocket screws
• Digital timer
• Non-waterproof UV LED strips
• 12 volt power supply (mine came with LEDs), or Amazon
• Soldering iron
• “hookup wire” to run LEDs continuously
• “Step Wedge” exposure calculator 
• Anthem Screen Printing Supply’s exposure calculator
• Ziplock Space Bags

First, I must say that this DIY screen printing exposure unit is a result of reading online tutorials and asking a lot of questions to other screen printers who’ve tackled this project. While I did add my own ideas, this is by no means my invention.

Box Construction

My first consideration for the DIY screen printing exposure unit was size. While I’d love a large “box” capable of handling much larger screens, I realized that any screen project larger than 20×24 was going to be pretty rare around here. The bread-and-butter size screen at my shop is 20×24″. So 21×25″ felt like a great size—especially not knowing how the system would work. Also, space is a premium in my shop, and this size is also very light and can be shelved quickly.

I created the box using 1/4″ plywood and pocket screws. (Pocket screws remain one of the greatest inventions for a project like this.) The I.D. of the box is 21×25″ so that the 20×24″ frame fits in with no trouble. The heigh of the box is 7.75″. Most importantly, the distance from the LEDs to the top of the screen is 6.25″. Why? Great question. Seemed like a good distance. Not real close but far enough to create a nice full, flood of light. I also used a jigsaw to cut two “hand holds” on the sides. This is not necessary, but it is nice when moving the unit, or lowering it on to your screen.

The LEDs are run in rows 21″ long and 1.5″ apart on center. Again, no real science to back this decision. Just felt right. Seemed again to create an even light without running more rows of light—the most expensive part of the build. And after looking at a few “real” LED units online, this distance between rows looked right. Note: do not purchase the waterproof version of the LEDs. Hopefully you will never use this unit underwater and more importantly, the waterproof strands have a coating to block UV light.

The LEDs are cut and using their built-in adhesive tape, stuck right to the plywood “deck”. The most time-consuming part of the project begins here: solder jumper wires from strip to strip to keep the power flowing.

A note on UV LED strips. The goal here is UV light in a specific wavelength range, I believe 360 nanometers (nm) or so. I was first interested in these lights, but went with a cheaper eBay option. If anyone uses the Waveformlighting.com lights, please let me know. I’m curious if their product would make a substantial difference, justifying the additional cost? Also: tons of useful information on their site about UV light.

Timer

On top of the unit sits a timer. The timer is not necessary. There’s no reason why you couldn’t plug the power supply in (or rig another style of timer) and count your exposure time and pull the plug. But I thought for another $17 the timer would be handy. And it looks cool. If you do install the timer, get ready for frustrating Chinese to English directions. I feel like the timer does a lot more—I just can’t wrap my head around the directions? Also be sure to get one for use with 12V power. There are a few on Amazon that look identical, but use 120V.

Another frustration with the timer is no wiring diagram, but I’ve got you covered! Fire up that soldering iron once again and check out my wiring diagram.

The Space Bag

There’s lots of debate on how best to attach film to emulsion. I think we can all agree that a vacuum system is best. Even the slightest bit of light bleeding from your film will create a blurry edge, or worse, total loss of detail. I began this project placing a piece of glass on top of the screen to sandwich the film to the emulsion. This worked pretty well, but many times it was clear that the film was not tight to the emulsion across the entire piece of art. It’s also a miracle that I didn’t cut myself picking up the glass multiple times in low light, placing it on the table where it became invisible, etc. It’s also an easy way to rip a screen with the sharp edge of the glass. Ask me how I know.

So today, I use a space bag as my cheap-o vacuum system. Granted, this step is time consuming—It sure would be great to place the screen down on a unit and hit a vacuum button, but those units come with a hefty price tag. For the amount of screens I create (2-4 a week), this system does a great job. The bags create a perfect amount of vacuum to hold the film tight. Remember, all we need is no light leak and the bag accomplishes this goal for just $15.00. Under the screen I place a piece of black foam core to keep light from coming “up” and striking the underside of my screen.

I know what you’re thinking? A space bag? But they have text and graphics printed on them! My ziplock branded bags have a clear “back”—use that side.
I can also hear you saying, “look how the space bag is not flat—it has some kinda pattern/texture in the plastic! Doesn’t that interfere with the film/art?” No. before I lower the unit over the screen I smooth out any big wrinkles from the film to be sure that the LED lights hit directly onto the film with no waves or creases that could leave a shadow.

I can also hear you saying, “is the bag blocking UV light? Great question. Maybe? But I have not seen any negative effects to the final burn. Images washout super sharp with tons of detail.

What’s my exposure time?

You’ll want to get out your screen exposure calculator and dial in appropriate burn times. Remember there are a lot of factors here: Screen mesh, emulsion brand, emulsion age, amount of emulsion—you get the idea. I can say that with Ulano’s Orange emulsion I burn a 230 mesh screen in 37 seconds. That’s one pass of emulsion on each side with the scoop coater’s sharp edge. Your mileage will vary.

For exposure calculators, I like the Anthem Screenprinting Supply version found here. I also burn most every screen with this exposure guide attached to a corner of the screen. Works great to dial in the exact time and I like to see that my burn times are still my burn times. This allows me to track the age and quality of my emulsion and double check that I’m getting consistent exposures.

Pros and Cons

Pros

• Super affordable! Total project can be built for under $100
• Easy to assemble—love those pocket screws!
• Nice even distribution of light. Unlike a bulb in the center, the strips provide much more equal light
• Fast exposure times
• No halogen bulbs creating unnecessary heat and a fire hazard

Cons

• Vacuum bagging system is cumbersome and slow
• The largest Space Bags only hold a 20×24″ screen 
• Would be great to have presets for times on the timer
• Would be better (albeit much more expensive) to have built-in vacuum system

So, that’s about it. I’m very pleased with the final product. I understand that there are some cumbersome steps here. (I’m looking at you, Space Bag) but know that for the amount of printing I do, maybe 2-3 projects a week, this system gets the job done. Someday I would love a “real” 30×40 LED unit with vacuum, etc. But that’s not in the budget right now. Plus, I really do not have the room.

So let me leave me a question in the comments, or tell me how you burn screens in your shop. Or how would you—or did you improve on this idea? Speaking of your shop, build this project at your own risk. My unit has been making beautiful screens for just about a year with no problems. But do know that you’re dealing with 120 volt household power and you can get yourself in a lot of trouble with even 12 volts. So be careful and don’t burn your shop down. That really defeats the purpose here.