When it comes to screen printing, there are several ways to expose your screens. Ideally, you’ll use an LED exposure unit like the Quick Image or an automated laser system such as the LTS 8012 (Laser-To-Screen) for precision, speed, and consistency. But what happens if your equipment malfunctions or you’re just starting out and don’t have an exposure unit yet? Believe it or not, the sun can be an effective backup exposure source.

In this blog post we’ll walk through exactly how to expose a screen using sunlight, along with practical tips to get the best results.

WATCH VIDEO: How To Expose Your Screen With The Sun

Why the Sun Works to Expose Screens

The sun emits UV light, which is the same energy that hardens screen printing emulsion during exposure. Temperature doesn’t matter. Hot or cold, as long as the sun is shining, it’s producing UV rays that will crosslink your emulsion.

What You’ll Need to Expose Your Screen with the Sun

• A sturdy base — A flat piece of wood works well; painting it black helps absorb stray UV
• A piece of glass — Ordinary flat glass (avoid plexiglass, which can flex and reduce contact)
• Your coated screen — Dry and ready to expose (in our demo video, we used ChromaBlue for its wide exposure latitude)
• Film positive — Place it on the print side of the screen
• Pressure plate — Another board (black is ideal) to hold the positive tightly against the screen

Step-by-Step: Sunlight Exposure

1. Build the stack: Base board → screen (print side up) → film positive → glass → top pressure plate.
2. Pick your moment: Aim for high noon so the sun’s rays are as perpendicular as possible.
3. Expose: Keep the setup covered until you’re ready. Uncover and expose in direct sun. With ChromaBlue under bright midday sun, a starting point can be ~20 seconds (conditions vary).
4. Cover and move indoors: After exposure, cover the screen and bring it to a light-safe area.
5. Wash out: Under subdued indoor lighting (avoid direct sunlight), rinse until image areas open cleanly. If the stencil looks soft or underexposed, increase exposure next time.

Tips for Best Results when Exposing Screens with the Sun

• UV, not heat: Exposure depends on UV intensity, not temperature.
• Keep it perpendicular: The screen should face the sun directly for even results.
• Mind the weather: Cloudy, rainy, or nighttime conditions won’t work.
• Use a forgiving emulsion: ChromaBlue is a great choice for sun exposures thanks to its wide latitude.
• Dial it in: Use an Exposure Calculator to fine-tune your exact time.

WATCH VIDEO: Dial In Exposure With A 10-Step Exposure Calculator

Note: In the demo, Mick uses ChromaBlue due to its wide exposure latitude. Always consult your emulsion’s user guide for recommended ranges and use an Exposure Calculator to dial in exact times for your setup.

Understanding Light Types for Screen Exposure

In the pursuit of saving costs, many beginners venture into DIY exposure units or purchase a secondhand unit. However, the choice of light source is often underestimated and can have a huge impact on the final results. All Chromaline emulsions (dual-cure, diazo, and pure photopolymer) respond best to UV light in the 350–420 nm range. Brightness you can see isn’t the key—wavelength is. Here’s how common light sources stack up:

• Mercury Vapor: Strong UV in the right range but runs very hot—can damage screens and is not beginner-friendly.
• Photo Flood Lights: May emit some UV, but output and wavelength vary widely; without specs, it’s a guess.
• Fluorescent Tubes: Standard “cool white” tubes are for room lighting. For exposure you need specialty blacklight tubes labeled around 350 nm. Effective, but UV output drops over time; replace sets together.
• Halogen: Very bright and very hot with little usable UV. Poor choice for exposing screens.
• Metal Halide: Industrial/pro models matched to 350–420 nm are excellent but costly. Hardware-store versions often have the wrong spectrum.
• Grow Lights: Can work with diazo-based emulsions, but they’re not designed for precise screen exposure.
• LED: Outstanding if engineered for ~365–400 nm. Generic “bright” LEDs without wavelength specs are unreliable for exposure.

Bottom line: If you’re DIY-ing, verify the light’s wavelength (350–420 nm). When in doubt, contact Chromaline for guidance on compatible light sources and exposure units.

WATCH VIDEO: Screen Exposure For Beginners... Will This Light Work?

Contact Chromaline Screen Print Products

Exposing with sunlight isn’t the preferred production method because it is weather-dependent and less consistent than LED or laser exposure. Still, in a pinch or when you’re starting out, it can produce perfectly usable stencils. With the right timing, materials, and a bit of and a bit of testing, you can harness the sun to keep your prints moving—until you’re ready to step up to a dedicated exposure unit. If you have any questions on exposing your screens for screen printing, check out our Exposure page or contact the Chromaline team for more information.