Exposure Calculator for Screen Printing

Screen Printing Exposure Calculator

Known Good Exposure Time (seconds):

Current Light Source Power (Watts):

New Light Source Power (Watts):

Current Distance (inches):

New Distance (inches):

function calculateExposure() { var knownExposureTime = parseFloat(document.getElementById("knownExposureTime").value); var currentLightPower = parseFloat(document.getElementById("currentLightPower").value); var newLightPower = parseFloat(document.getElementById("newLightPower").value); var currentDistance = parseFloat(document.getElementById("currentDistance").value); var newDistance = parseFloat(document.getElementById("newDistance").value); var resultDiv = document.getElementById("exposureResult"); if (isNaN(knownExposureTime) || isNaN(currentLightPower) || isNaN(newLightPower) || isNaN(currentDistance) || isNaN(newDistance) || knownExposureTime <= 0 || currentLightPower <= 0 || newLightPower <= 0 || currentDistance <= 0 || newDistance <= 0) { resultDiv.innerHTML = "Please enter valid positive numbers for all fields."; return; } // Formula: New Exposure Time = Old Exposure Time * ( (New Distance / Old Distance)^2 ) * (Old Power / New Power) // This formula accounts for the inverse square law for distance and direct proportionality for power. // If distance decreases, intensity increases, so exposure time decreases. (New Distance / Old Distance)^2 will be < 1 if New Distance < Old Distance. // If power increases, intensity increases, so exposure time decreases. (Old Power / New Power) will be Old Power. var distanceFactor = Math.pow(newDistance / currentDistance, 2); var powerFactor = currentLightPower / newLightPower; var calculatedExposure = knownExposureTime * distanceFactor * powerFactor; resultDiv.innerHTML = "

Calculated New Exposure Time:

" + calculatedExposure.toFixed(2) + " seconds"; } .calculator-container { background-color: #f9f9f9; border: 1px solid #ddd; padding: 20px; border-radius: 8px; max-width: 600px; margin: 20px auto; font-family: Arial, sans-serif; } .calculator-container h2 { text-align: center; color: #333; margin-bottom: 20px; } .calculator-input { margin-bottom: 15px; } .calculator-input label { display: block; margin-bottom: 5px; font-weight: bold; color: #555; } .calculator-input input[type="number"] { width: calc(100% – 22px); padding: 10px; border: 1px solid #ccc; border-radius: 4px; box-sizing: border-box; } button { background-color: #007bff; color: white; padding: 12px 20px; border: none; border-radius: 4px; cursor: pointer; font-size: 16px; width: 100%; box-sizing: border-box; } button:hover { background-color: #0056b3; } .calculator-result { margin-top: 20px; padding: 15px; border: 1px solid #e0e0e0; border-radius: 4px; background-color: #eaf6ff; text-align: center; } .calculator-result h3 { color: #333; margin-top: 0; } .calculator-result p { font-size: 1.2em; font-weight: bold; color: #007bff; }

Understanding Screen Printing Exposure and How to Use This Calculator

Screen printing is a versatile and popular printing method, but achieving crisp, durable stencils requires precise control over the exposure process. The exposure unit uses UV light to harden the emulsion on your screen, creating the stencil. Too little exposure, and your stencil will wash out prematurely; too much, and fine details can be lost, or the emulsion can become brittle.

What is Screen Printing Exposure?

Exposure in screen printing refers to the process of hardening a light-sensitive emulsion on a screen mesh using ultraviolet (UV) light. Areas of the screen covered by your film positive (the dark parts of your design) block the UV light, preventing the emulsion underneath from hardening. When the screen is washed out, these unhardened areas dissolve, creating the open stencil through which ink will pass.

Key Factors Affecting Exposure Time:

Emulsion Type: Different emulsions have varying sensitivities to UV light. Some are "faster" (require less exposure), while others are "slower." Always start with the manufacturer's recommendations.
Light Source Type and Power: The type of UV light source (e.g., metal halide, UV LED, fluorescent black lights) and its wattage or intensity significantly impact exposure time. Higher power generally means shorter exposure times.
Distance from Light Source to Screen: The inverse square law applies here: the intensity of light decreases rapidly as the distance from the source increases. Moving the light closer dramatically reduces exposure time.
Film Positive Density: A truly opaque film positive is crucial. Any transparency in the dark areas will allow UV light to penetrate, leading to underexposure of those areas and loss of detail.
Mesh Count: While less impactful than light source or distance, very high mesh counts (finer threads) can sometimes require slight adjustments.
Emulsion Over Mesh (EOM) Thickness: A thicker stencil (more emulsion built up on the mesh) will generally require slightly longer exposure to ensure full hardening.

Why Use an Exposure Calculator?

Finding the perfect exposure time is often a process of trial and error, typically starting with a step wedge test. However, once you've established a good baseline exposure time for a specific setup, you might need to adjust it if you change your equipment. This calculator helps you predict a new exposure time when you alter your light source's power or its distance from the screen, saving you time and emulsion.

How This Calculator Works:

This calculator uses the principles of light intensity to help you adjust your exposure time. It takes into account:

Inverse Square Law for Distance: Light intensity is inversely proportional to the square of the distance from the source. If you halve the distance, the intensity becomes four times greater, meaning you'll need significantly less exposure time.
Direct Proportionality for Power: A more powerful light source (higher wattage) emits more UV energy, leading to shorter exposure times.

By inputting your known good exposure time, your current light source's power and distance, and your new desired power and distance, the calculator provides an estimated new exposure time. This helps you get much closer to the correct setting without extensive re-testing.

Tips for Perfect Exposure:

Always do a step test: Even with this calculator, a physical step test (using an exposure calculator strip) is the best way to fine-tune your settings for your specific emulsion, light source, and environment.
Consistency is key: Keep your variables (emulsion thickness, film density, light source, distance) as consistent as possible.
Monitor your light source: UV bulbs degrade over time, requiring longer exposure. Keep track of bulb hours.
Cleanliness: Dust on your film positive or screen can block UV light, causing pinholes or underexposed areas.

Use this calculator as a smart starting point or adjustment tool, but always verify with a physical test for optimal results in your screen printing darkroom.