Screen Printing Exposure Calculator

Easily determine the correct exposure time for your screen printing projects with our Screen Printing Exposure Calculator.

Exposure Calculator

Exposure Time Chart

Chart showing calculated exposure time vs. distance for two different light power levels (New Power and 0.8 * New Power).

Typical Mesh & Emulsion Factors

Mesh Count Range	Typical EOM	Mesh Factor (Approx.)	Emulsion Type	Sensitivity Factor (Approx.)
60-110	Thicker	0.9	Photopolymer (Fast)	0.7
125-180	Standard	1.0	Dual-Cure (Standard)	1.0
195-255	Thinner	1.1	Diazo (Slow)	1.5
280-305+	Very Thin	1.2-1.3	Dual-Cure (Standard)	1.0

These are approximate factors. Always perform a step wedge test to confirm your ideal exposure time.

What is a Screen Printing Exposure Calculator?

A Screen Printing Exposure Calculator is a tool used by screen printers to estimate the correct amount of time a screen coated with light-sensitive emulsion needs to be exposed to a UV light source to properly harden the emulsion around the artwork, creating a stencil. Getting the exposure time right is crucial for achieving sharp, durable stencils.

Anyone involved in screen printing, from beginners to experienced professionals, should use a Screen Printing Exposure Calculator or perform exposure tests. It helps save time and materials by reducing the number of mis-exposed screens. A common misconception is that one exposure time fits all scenarios; however, time varies significantly with mesh count, emulsion type, light source, and distance.

Screen Printing Exposure Formula and Mathematical Explanation

The core principle behind exposure calculation often relates to the inverse square law for light intensity and the sensitivity of the emulsion. The basic formula our Screen Printing Exposure Calculator uses is:

New Exposure Time = Base Time × (New Distance / Base Distance)² × (Base Power / New Power) × Mesh Factor × Emulsion Factor

Where:

• Base Time is a known good exposure time for a reference setup.
• (New Distance / Base Distance)² accounts for the change in light intensity due to distance (Inverse Square Law – intensity decreases with the square of the distance).
• (Base Power / New Power) accounts for changes in the light source’s power or intensity.
• Mesh Factor adjusts for the influence of mesh count (which affects Emulsion Over Mesh or EOM).
• Emulsion Factor adjusts for the relative sensitivity of different emulsion types.

Variable	Meaning	Unit	Typical Range
Base Time	Known correct exposure time	Seconds	30 – 900
Base Distance	Distance for base time	Inches	15 – 30
Base Power	Power for base time (or relative)	Watts/Relative	50 – 5000
New Distance	New distance from light	Inches	15 – 30
New Power	New light power (or relative)	Watts/Relative	50 – 5000
Mesh Factor	Adjustment for mesh count	Factor	0.8 – 1.5
Emulsion Factor	Adjustment for emulsion type	Factor	0.6 – 1.6

This Screen Printing Exposure Calculator provides a good starting point based on these relationships.

Practical Examples (Real-World Use Cases)

Example 1: Changing Distance

You have a good exposure time of 240 seconds at 20 inches with a 1000W light, 156 mesh, and standard emulsion. You move your light to 25 inches.

• Base Time: 240s
• Base Distance: 20 inches
• Base Power: 1000
• New Distance: 25 inches
• New Power: 1000
• Mesh Factor: 1.0
• Emulsion Factor: 1.0

Calculated Time = 240 * (25/20)² * (1000/1000) * 1.0 * 1.0 = 240 * 1.5625 = 375 seconds. The Screen Printing Exposure Calculator would show this.

Example 2: Changing Emulsion and Mesh

You switch from a 156 mesh with dual-cure (Base Time 180s at 20 inches, 1000W) to a 230 mesh and a faster photopolymer emulsion, keeping distance and power the same.

• Base Time: 180s
• Base Distance: 20 inches
• Base Power: 1000
• New Distance: 20 inches
• New Power: 1000
• Mesh Factor: 1.1 (for 230 mesh)
• Emulsion Factor: 0.7 (for photopolymer)

Calculated Time = 180 * (20/20)² * (1000/1000) * 1.1 * 0.7 = 180 * 1 * 1 * 0.77 = 138.6 seconds. Our Screen Printing Exposure Calculator helps make these adjustments.

How to Use This Screen Printing Exposure Calculator

1. Enter Base Values: Input a known good exposure time, and the distance and power settings used to achieve it.
2. Enter New Values: Input the new distance and/or power you intend to use.
3. Select Factors: Choose the mesh and emulsion factors that best match your new setup.
4. Calculate: The calculator will automatically update the “Calculated Time”.
5. Read Results: The primary result is the estimated new exposure time. Intermediate factors show how distance and power changes contribute.
6. Decision-Making: Use the calculated time as a starting point for your exposure tests (like a step wedge test). Fine-tune based on test results.

Always bracket your exposures (do tests slightly above and below the calculated time) when using a new setup or after using the Screen Printing Exposure Calculator.

Key Factors That Affect Screen Printing Exposure Results

• Light Source Type & Power: Different lights (LED, metal halide, fluorescent) have different UV outputs and spectral characteristics. Higher power generally means shorter times, but the type of UV is crucial. Our Screen Printing Exposure Calculator uses relative power/intensity.
• Distance from Light Source: Light intensity decreases with the square of the distance (Inverse Square Law). Doubling the distance reduces intensity to one-quarter.
• Emulsion Type and Coating Thickness: Photopolymers expose faster than dual-cures or diazos. Thicker emulsion coats (EOM – Emulsion Over Mesh) require longer exposure. See our emulsion guide.
• Mesh Count and Color: Higher mesh counts often have thinner EOM, but can also scatter light differently. Dyed/yellow mesh can require slightly longer times than white mesh as it absorbs more UV. Learn about mesh selection.
• Humidity and Temperature: High humidity can affect emulsion sensitivity and drying, potentially altering exposure needs.
• Age of Bulb and Emulsion: UV bulbs lose intensity over time, and emulsion loses sensitivity, especially if stored improperly.
• Artwork Density: Very fine lines or halftones might require slightly different exposure than bold block areas to hold detail.

The Screen Printing Exposure Calculator helps adjust for some of these, but regular testing is key.

Frequently Asked Questions (FAQ)

What is the best way to find my “Base Time”?

Use an exposure calculator strip or perform a step wedge test. This involves exposing different sections of a screen for different times and finding the time that gives the best washout and durability.

How accurate is this Screen Printing Exposure Calculator?

It provides a good estimate based on the provided factors and the inverse square law. However, it’s a starting point, and you should always confirm with a test exposure, as many variables are involved.

Why does mesh count affect exposure time?

Higher mesh counts usually result in a thinner layer of emulsion (EOM) being deposited, which may require slightly more time to fully cross-link, although less emulsion volume is present. The factors are approximations. More info at our screen printing basics page.

Can I use this calculator for LED and Metal Halide lights?

Yes, but you need to use a consistent measure of “Power/Intensity.” If you know the wattage and it’s the same type of light, you can compare. If switching light types (e.g., from fluorescent to LED), the wattage isn’t directly comparable; you’d need a relative intensity measure or do a new base test with the new UV light sources.

What if my light source power is unknown?

You can use relative values. If you think one setup is twice as intense as another, use values like 100 and 200, or 1 and 2. The ratio is what matters.

Does the color of the mesh matter?

Yes, yellow or orange dyed mesh absorbs more UV light than white mesh and generally requires 10-30% more exposure time. Our calculator doesn’t have a separate factor for this, so you might add a small percentage manually or consider it in your base time.

What happens if I over or under-expose?

Under-exposure leads to a soft, slimy stencil that washes out too easily, losing detail. Over-exposure makes the stencil hard to wash out, and fine details might be lost or clogged. See troubleshooting exposure.

How often should I check my exposure times?

Regularly, especially if you change bulbs, emulsion batches, or notice changes in your stencil quality. Using a Screen Printing Exposure Calculator helps when you make intentional changes.