Screen Exposure Calculator

Screen Exposure Calculator for Screen Printing

Achieving the perfect screen exposure is one of the most critical steps in screen printing. It directly impacts the quality, detail, and durability of your stencil. Underexposed screens can lead to premature stencil breakdown, loss of fine details, and pinholes, while overexposed screens can result in difficulty washing out fine lines and details, leading to clogged mesh.

Understanding Screen Exposure

Screen exposure is the process of hardening the emulsion on your screen using a UV light source. The artwork (positive) blocks the UV light in the image areas, preventing the emulsion there from hardening. The unhardened emulsion is then washed away, leaving an open stencil for ink to pass through.

Key Factors Affecting Exposure Time:

  • Light Source Power (Watts): Higher wattage UV lamps emit more intense light, requiring shorter exposure times.
  • Light Source Distance (Inches/cm): The inverse square law applies here. As the distance between the light source and the screen increases, the light intensity decreases significantly, requiring longer exposure times. Doubling the distance quadruples the exposure time.
  • Emulsion Type: Different emulsions have varying sensitivities to UV light. Fast-exposing emulsions require less time, while slower emulsions need more.
  • Mesh Count: While less impactful than light source and distance, very high mesh counts (finer threads) can sometimes require slightly longer exposure due to the increased density of the mesh itself.
  • Film Positive Density: A truly opaque film positive is crucial. Any transparency will allow UV light to penetrate, leading to stencil breakdown.

How to Use the Screen Exposure Calculator

This calculator helps you adjust your exposure time when you change your light source power or distance, based on a known good exposure time from a reference setup. This is particularly useful when upgrading equipment or moving your exposure unit.

  1. Base Exposure Time: Enter the exposure time (in seconds) that you know works perfectly for a specific setup.
  2. Reference Light Power: Enter the wattage of the light source used for that "known good" exposure.
  3. Reference Light Distance: Enter the distance (in inches) from the light source to the screen for that "known good" exposure.
  4. Current Light Power: Enter the wattage of the light source you are currently using or plan to use.
  5. Current Light Distance: Enter the distance (in inches) from your current light source to the screen.

The calculator will then provide a recommended exposure time for your new setup.

Example Scenario:

Let's say you know that with a 500 Watt light source positioned 15 inches from your screen, your emulsion exposes perfectly in 25 seconds. Now, you've upgraded to a 1000 Watt light source and want to expose at a distance of 20 inches. Input these values into the calculator:

  • Base Exposure Time: 25 seconds
  • Reference Light Power: 500 Watts
  • Reference Light Distance: 15 inches
  • Current Light Power: 1000 Watts
  • Current Light Distance: 20 inches

The calculator will then determine the new recommended exposure time for your updated setup.

Tips for Perfect Exposure

  • Step Test: Always perform a step test (or exposure calculator test) when setting up a new exposure unit or changing emulsion types. This calculator provides a good starting point, but a physical test is essential for fine-tuning.
  • Cleanliness: Ensure your exposure unit glass and screen are free of dust and debris.
  • Vacuum: If your unit has a vacuum blanket, ensure it pulls a tight vacuum to create perfect contact between the film positive and the emulsion.
  • Consistency: Try to maintain consistent conditions (temperature, humidity) in your darkroom, as these can subtly affect emulsion performance.

By understanding the principles of screen exposure and utilizing tools like this calculator, you can significantly improve the consistency and quality of your screen printing stencils.

Screen Exposure Calculator

Recommended Exposure Time: 0 seconds
function calculateExposure() { var baseExposureTime = parseFloat(document.getElementById('baseExposureTime').value); var refLightPower = parseFloat(document.getElementById('refLightPower').value); var refLightDistance = parseFloat(document.getElementById('refLightDistance').value); var newLightPower = parseFloat(document.getElementById('newLightPower').value); var newLightDistance = parseFloat(document.getElementById('newLightDistance').value); // Validate inputs if (isNaN(baseExposureTime) || baseExposureTime <= 0 || isNaN(refLightPower) || refLightPower <= 0 || isNaN(refLightDistance) || refLightDistance <= 0 || isNaN(newLightPower) || newLightPower <= 0 || isNaN(newLightDistance) || newLightDistance <= 0) { document.getElementById('exposureResult').innerHTML = 'Please enter valid positive numbers for all fields.'; document.getElementById('exposureResult').style.backgroundColor = '#f8d7da'; document.getElementById('exposureResult').style.borderColor = '#f5c6cb'; document.getElementById('exposureResult').style.color = '#721c24'; return; } // Calculate the new exposure time // Formula: New Exposure Time = Base Exposure Time * (Reference Light Power / Current Light Power) * (Current Light Distance / Reference Light Distance)^2 var powerFactor = refLightPower / newLightPower; var distanceFactor = Math.pow((newLightDistance / refLightDistance), 2); var calculatedExposure = baseExposureTime * powerFactor * distanceFactor; document.getElementById('exposureResult').innerHTML = 'Recommended Exposure Time: ' + calculatedExposure.toFixed(2) + ' seconds'; document.getElementById('exposureResult').style.backgroundColor = '#e9f7ef'; document.getElementById('exposureResult').style.borderColor = '#d4edda'; document.getElementById('exposureResult').style.color = '#155724'; } // Initial calculation on page load for default values window.onload = function() { calculateExposure(); };

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