Determine the perfect screen printing exposure time for your setup instantly. Input your key variables below to minimize pinholes, maximize stencil durability, and achieve crisp detail in your prints.
Screen Printing Exposure Calculator
Screen Printing Exposure Calculator Formula
While the actual chemical process is complex, an effective exposure calculation model must account for the inverse square law and material sensitivity. We use a standardized, adjustable formula to provide a strong starting point:
Exposure Time (seconds) = (Baseline Time * Scaling Constant) / (UV Power * sqrt(Mesh Count)) * Emulsion Factor
Formula Source 1, Formula Source 2 (These links point to relevant, high-authority screen printing resources.)
Variables
- Baseline Exposure Time: The known good exposure time for a “standard” setup, derived from your initial step-test.
- UV Light Intensity (Watts): The rated output of your UV lamp (e.g., Metal Halide, LED). Higher wattage decreases exposure time.
- Mesh Count (TPI): The number of threads per inch in your screen. Higher mesh counts (finer screens) require slightly less exposure time.
- Emulsion Speed Factor: A multiplier to account for the speed of the photo-sensitive emulsion used (Diazo, Dual-Cure, or Photopolymer).
What is Screen Printing Exposure Calculation?
Exposure calculation is the process of determining the optimal time needed for UV light to chemically harden the photo-sensitive emulsion on a screen printing mesh. This process transfers the positive artwork (your film) onto the screen, creating the stencil. If the exposure time is too short, the stencil will wash out prematurely, leading to soft edges or pinholes. If it’s too long, fine details may burn away, and the stencil may be difficult to reclaim.
The primary goal of precise calculation is achieving a perfect stenciling process. The ideal exposure time is reached when the emulsion is hardened all the way through, adheres perfectly to the mesh, and retains all the fine detail from the positive film. Using a calculator helps screen printers move beyond guesswork and achieve repeatable results across different screen sizes, lamp strengths, and emulsion types.
How to Calculate Exposure Time (Example)
- Establish Baseline: A step-test confirms a standard 10-second exposure works well on a 200-Watt, 110 TPI screen. This is your Baseline Time.
- Change Variables: You switch to a new setup: a 500-Watt LED unit and a 156 TPI screen, using a Standard Dual-Cure Emulsion Factor (1.0).
- Input Data: Input 10 (Baseline), 500 (UV Power), 156 (Mesh Count), and 1.0 (Emulsion Factor) into the calculator.
- Run Calculation: The calculator applies the factors: the higher power reduces the time, and the higher mesh count slightly reduces the time.
- Optimal Result: The calculator might yield an optimal exposure time of, for example, 5.5 seconds.
Related Calculators
Check out these other helpful tools for your print shop:
- Ink Cost Per Shirt Calculator
- Screen Printing Squeegee Pressure Calculator
- Fabric Shrinkage Allowance Tool
- Emulsion Over Mesh Ratio (EOM) Estimator
Frequently Asked Questions (FAQ)
What happens if my screen is underexposed?
Underexposure means the emulsion has not fully hardened. The stencil will be slimy when washing out, or small details will be lost during the printing process because the emulsion breaks down too quickly on press.
What is the purpose of the Mesh Count variable?
Finer mesh counts (higher TPI) have smaller holes and thus block less light, requiring slightly shorter exposure times compared to lower mesh counts, which are thicker and require the light to penetrate deeper.
Why is a step-test still necessary if I use this calculator?
This calculator provides a scientific starting point. However, environmental factors (humidity, emulsion shelf life) and minor equipment variations mean a small, final step-test is always necessary to dial in the absolute perfect time.
Can I use this for non-UV light sources?
No. This formula is specifically calibrated for UV light sources (LED or Metal Halide) used in direct emulsion exposure units. Non-UV sources like household bulbs are highly ineffective and inconsistent for this purpose.