Screen Printing Exposure Calculator
Plan a step-wedge test, correct a 21-step reading, or rescale a known time when you move the lamp.
This screen printing exposure calculator runs in your browser. It plans a cover-strip test, corrects a Stouffer-style 21-step reading, or rescales a time you already proved when the lamp moves. Nothing is uploaded.
Fully local. No account and no limit. Nothing is uploaded. UV can harm eyes and skin, so do not look at the lamp.
Expose every strip for the base time first, with the card off. Then cover strips from the last one backward. Each extra increment keeps the lower-numbered strips exposing, so strip 1 gets every increment (the longest time) and the last strip stays at the base time (the shortest).
Whole number from 2 to 12.
After washout, choose the shortest strip where the emulsion is fully hard and fine detail still washes out clean. If every strip washed away, start again with a longer base time. If every strip is closed up, use a shorter base.
This assumes a Stouffer T2115-style 21-step wedge: 0.15 density per step, which is half a stop. Other wedges are not supported. Count only the highest fully solid step.
Whole number from 1 to 21. Crusty or partly open steps do not count.
Ulano describes a solid step 7 as the minimum full exposure for direct emulsion. SAATI’s data sheet describes 7 remaining steps as a typical target, and 6 for CtS. Indirect film may target step 6. Change the target if your process says so.
If you use a manufacturer filter film, such as Chromaline One Step, follow that film’s instructions instead of this factor.
Formula. new time = known time × (new distance ÷ known distance)²
Screen printing exposure step-test worksheet
Fill in the blanks before you expose. The times below are the plan for this test only.
Expose every strip for the base time first, with the card off. Then cover strips from the last one backward. Each extra increment keeps the lower-numbered strips exposing, so strip 1 gets every increment (the longest time) and the last strip stays at the base time (the shortest).
- Emulsionblank line to write in
- Meshblank line to write in
- Lampblank line to write in
- Distanceblank line to write in
- Coatsblank line to write in
- Dateblank line to write in
- Best stripblank line to write in
| Strip | Total time |
|---|---|
| 1 | 70 seconds |
| 2 | 60 seconds |
| 3 | 50 seconds |
| 4 | 40 seconds |
| 5 | 30 seconds |
| 6 | 20 seconds |
Uncover / cover schedule
| Clock | Action |
|---|---|
| 0 seconds | Start. Every strip is uncovered. |
| 20 seconds | At 20 seconds, cover strip 6. |
| 30 seconds | At 30 seconds, cover strip 5. |
| 40 seconds | At 40 seconds, cover strip 4. |
| 50 seconds | At 50 seconds, cover strip 3. |
| 60 seconds | At 60 seconds, cover strip 2. |
| 70 seconds | At 70 seconds, cover strip 1. The test is complete. |
After washout, choose the shortest strip where the emulsion is fully hard and fine detail still washes out clean. If every strip washed away, start again with a longer base time. If every strip is closed up, use a shorter base.
How to use this screen printing exposure calculator
Pick the job in front of you
Use the step-test planner when you do not yet have a time for this emulsion, mesh, coating, and lamp. Use the 21-step correction when you already exposed a Stouffer-style wedge and read the highest fully solid step. Use the lamp-distance tool only when a time already worked and you moved that same lamp.
Set seconds or minutes, and inches or centimeters
The unit switches convert the numbers already in the fields. Type the time and the distance you measured. A time copied from another shop’s lamp is a rumor until you test it on yours.
Read the planner as a schedule, then print the worksheet
The planner lists each strip’s total time and the clock time when you cover that strip. Print the worksheet and write the emulsion, mesh, lamp, distance, coats, and date before you expose. The winning strip is only useful if those notes are on the same page.
Wash out, then keep the shortest strip that is actually open
After the screen is dry, choose the shortest strip where the emulsion is fully hard and fine detail still washes out clean. If every strip washes away, start again with a longer base. If every strip is closed up, use a shorter base.
Confirm a corrected time on a new screen
A 21-step factor and a distance rescale are the next test, not a finished setting. Expose a new screen at the new time. If you changed emulsion, mesh count or color, coating, lamp, or distance, run another step test.
Plan a step-wedge (cover-strip) test
A step-wedge test, also called a cover-strip test, puts several exposure times on one coated screen. Dry the mesh the way you do for a job. An opaque card blocks the UV. Number the strips before you start, and do not renumber them after washout.
Expose every strip for the base time first, with the card off. The base time is the shortest strip. Then cover the last strip. Each extra increment leaves the lower-numbered strips uncovered, so they keep exposing. Strip 1 receives the base time plus every increment and is the longest. The last strip stays at the base time. The table lists the total for each strip. The schedule is cumulative clock time: at T, cover strip N.
Six steps is the default. You can plan anywhere from 2 to 12. Keep the increment wide enough that neighbors will not look the same after washout. If the only acceptable strip is the longest or the shortest, the answer is outside this test. Lengthen the base when the whole screen washes away. Shorten it when the whole screen is closed, then plan the test again.
Hold the card flat so the boundary stays a hard line, and move it only at the clock times. Light leaking under a curled corner mixes the strips, and the table no longer describes the screen. After washout and drying, choose the shortest strip where the emulsion is fully hard and fine detail still washes out clean. A longer strip that also looks fine is more exposure than this screen needed.
Write that time on the worksheet with the emulsion, the mesh count and color, the lamp, the distance, and the coats on each side. The time belongs to that setup. The printed page is a record plus the schedule calculated here. It is not a manufacturer’s exposure calculator film. If your emulsion’s instructions require that maker’s own film or chart, use the film.
Correct a 21-step wedge reading
A 21-step sensitivity guide is a small film with 21 patches. This calculator assumes a Stouffer T2115-style wedge: 0.15 density per step, which is half a stop. A full stop doubles or halves the time, so two steps change the time by a factor of two. Other step counts and other density increments are not supported. Stouffer’s notes on using a 21-step wedge describe how to read the solid steps on that film.
Expose the guide in contact with the emulsion, wash out, and count only the highest fully solid step. A crusty step, or a step that is stained but still open, does not count. If you read step 1 or step 21, the reading may be off the wedge’s range. Change the time substantially and retest. The factor is still shown so you can see the direction, and it is not a precise correction when the truth is off the film.
D is the target step minus the step you observed. F is 2 raised to D/2. The new time is the test time multiplied by F. One step short of the target multiplies time by about 1.41. Two steps short doubles it. One step over multiplies by about 0.71. Positive D means underexposed, so the new time is longer. Negative D means overexposed, so the new time is shorter. Zero means the reading is on target.
D = target − observed
F = 2^(D/2)
new time = test time × F
The tool also prints the same relationship on one line, and it multiplies by the exact power of two rather than by a rounded chart.
new time = test time × 2^((target − observed) / 2)
| Steps from target | Rounded factor |
|---|---|
| +1 | 1.41× |
| +2 | 2.00× |
| +3 | 2.83× |
| +4 | 4.00× |
| −1 | 0.71× |
| −2 | 0.50× |
| −3 | 0.35× |
| −4 | 0.25× |
Ulano’s exposure notes describe a solid step 7 as the minimum full exposure for direct emulsion. SAATI’s 21-step technical data sheet describes 7 remaining steps as a typical target, and 6 for computer-to-screen (CtS). Indirect film may target step 6. The target field starts at 7, and you can change it to the step your own technical data sheet names.
Expose a new screen at the new time to confirm. Washout pressure, humidity, and a lamp that has aged since the test can all move the stencil. A manufacturer filter film, such as Chromaline One Step, is a different object. Follow that film’s instructions. Do not type its row numbers into this factor.
Adjust exposure time when the lamp distance changes
If a time already worked and you only moved that lamp, you can rescale it. The page uses the inverse-square law. Twice as far needs about four times the time. Half as far needs about a quarter of the time.
new time = known time × (new distance ÷ known distance)²
Chromaline’s exposure guide publishes a worked example: 3 minutes at 1 meter, 12 minutes at 2 meters, and 27 minutes at 3 meters. Type 3 minutes with 100 cm and 200 cm and the result is 12 minutes. From 100 cm to 300 cm the result is 27 minutes.
The square is most accurate for a small or point source far from the screen, such as a metal-halide lamp a few feet away. A close LED array or a bank of tubes sends light from many points, and the estimate deviates. Treat the new time as a starting estimate and run a new step test. The inverse-square law is not exact for every LED unit.
Measure from the same place each time, either the lamp face or the bulb center, out to the mesh. If the lamp, the emulsion, or the coating changed as well, the old time is no longer known-good. Use the step-test planner instead of the square.
Starting ranges by light source
Nothing below is a production exposure. The figures are rough starting estimates so the first step test begins in a plausible range. Follow your emulsion’s technical data sheet, then prove the time on your screen. This page does not calculate an exposure from an emulsion name, a wattage, and a mesh count. Coating thickness, spectrum, and washout are still free to change the result.
| Light source | Rough starting estimate | Source |
|---|---|---|
| LED exposure unit | Roughly 10 seconds to 2 minutes. Photopolymer is usually faster. The time varies with wavelength, power, and emulsion. | Screen Print Help exposure notes |
| Metal halide (point source) | Roughly 30 seconds to 3 minutes. The time varies with wattage and distance. | Screen Print Help exposure notes |
| Fluorescent / UV tube unit | Roughly 2 to 10 minutes. Tubes age, so retest. | Screen Print Help exposure notes |
| Sunlight | Under a minute to several minutes. Time of day, season, clouds, and location all change it, and the result is hard to repeat. | Screen Print Help exposure notes |
| Speedball instruction book, sunlight | 45 seconds. | Speedball instruction book |
| Speedball 30W UV LED floodlight, 8×10 in at 16 in | 7 minutes. | Speedball instruction book |
| Speedball 30W UV LED floodlight, 10×14 in at 16 in | 8 minutes. | Speedball instruction book |
| Speedball 30W UV LED floodlight, 12×18 in at 18 in | 10 minutes. | Speedball instruction book |
| Speedball 30W UV LED floodlight, 16×20 in at 20 in | 12 minutes. | Speedball instruction book |
| Speedball Speed Screen, 10×12 in at 14 in | 1 minute. | Speedball instruction book |
| Speedball Speed Screen, 12.5×16.5 in at 19 in | 2 minutes. | Speedball instruction book |
Under the same lamp, pure photopolymer is usually much faster than diazo and dual-cure. That line is qualitative: there is no second count attached to it. Retest when the emulsion, mesh count or color, coating, lamp, or distance changes. Ulano’s exposure notes say to establish exposure on the stencil you are using and to check again after a process change. Sunlight also moves with the hour, the season, and the clouds, so a sun time is hard to repeat.
Frequently asked questions
Can this calculator give me one universal exposure time?
No. Exposure depends on your emulsion, mesh, coating, lamp, distance, and how you wash out the screen. Use the tool to plan a test or to adjust a time you already proved on your own setup, then confirm with a new stencil.
How do I run a step-wedge (cover-strip) test?
Coat and dry a test screen as you normally would. Use an opaque card to give each strip a different total time (the planner lists the uncover schedule). Wash out and dry the screen, then pick the shortest time where the emulsion is fully hard and fine detail still washes out clean. If every strip washes away, start again with a longer base time; if every strip is closed up, use a shorter base.
What is a 21-step wedge, and why do people aim for step 7?
A 21-step wedge is a small film with 21 densities, often a Stouffer T2115 or a SAATI / similar sensitivity guide. After washout, the highest fully solid step is a reading of how hard the stencil is. Ulano describes a solid step 7 as the minimum full exposure for direct emulsion; SAATI describes 7 remaining steps as a typical target (and 6 for CtS). If your process specifies a different target, change it in the calculator. This tool does not replace a calibrated wedge.
I moved the lamp. How do I change the time?
If you already have a good time at a measured distance, rescale it with the inverse-square law: multiply the time by the square of (new distance ÷ old distance). Twice as far needs about four times the time. This is a starting estimate and is less reliable for close LED arrays or tube banks than for a small lamp farther away. Run a new step test to confirm.
How long should I expose Speedball emulsion, or expose in the sun?
There is no single answer. Speedball’s instruction book gives rough estimates only: 45 seconds in sunlight, and, for their 30W UV LED floodlight, about 7 to 12 minutes depending on frame size and lamp height (for example, 8×10 inches at 16 inches for 7 minutes). Treat those as starting points for a step test, not as production times. Sunlight also changes with time of day, season, and cloud cover.
Is this a downloadable exposure calculator film? Do you upload my numbers?
The planner can print a worksheet. It is not a copy of a manufacturer’s calibrated calculator film. All calculations run in your browser; nothing is uploaded.
More maker calculators
Other published calculators on this site are linked below. Each one is a separate tool for a different job.