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Exposure Calculator

1 · Step-wedge test
Not sure what your exposure time should be? Start here. A step test is how you find the correct exposure time. You expose one screen in strips (steps), each for a different time. After washout, the best step is the shortest time where the emulsion is fully hard and your fine detail still washes out clean. That step's time is your exposure time. Re-test when you change emulsion, mesh, coats or light.
Mode? Base time?sec Incrementsec? Number of steps?
Step 1 gets the base time, the last step gets the longest. Start with everything uncovered except as shown in the schedule, or follow the schedule from the right.
2 · Time adjuster (estimates)
Current good time?sec
Light distance you tested with?Light distance now?
Coats you tested with?Coats now?
Mesh change?Dyed mesh extra?%
Lamp output lost?%
All adjusted times are estimates. Confirm with a new exposure test.

Cover-strip schedule

Lay the film positive, then cover the screen with an opaque card. Expose, sliding the card to uncover one more section at each listed moment, so the first section uncovered gets the longest time. Wash out, then click the step whose detail held best without being underexposed (soft, slimy or washing away) or overexposed (fine detail closed up).

Adjusted times (estimates)

ChangeRuleNew time

Distance uses the inverse-square law, which holds best for a small point-like source such as a single metal halide bulb at a distance; it is less accurate for close LED arrays and tube banks. Coats are scaled proportionally, which is only a rough guide because coat thickness varies with coater and technique. The dyed-mesh percentage is yours to set; dyed mesh reduces light scatter and usually needs more time, but how much varies by mesh, emulsion and light, so test it.

Typical starting ranges by light source

Light sourceRough starting rangeNotes
LED exposure unitAbout 10 seconds to 2 minutesVaries widely with LED wavelength, power and emulsion type. Photopolymer emulsions are usually fastest.
Metal halide (point source)About 30 seconds to 3 minutesDepends on wattage and distance. A point source holds fine detail well.
Fluorescent / UV tube unitAbout 2 to 10 minutesTubes lose output as they age, so retest from time to time.
SunlightFrom under a minute to several minutesChanges with time of day, season, cloud cover and location. Hard to repeat.
These are rough starting points only, not recommendations. Your emulsion manufacturer's specifications and your own exposure test govern. Diazo and dual-cure emulsions generally need much longer than pure photopolymer under the same light.

What each box means

New to screen printing? Here is what every box above asks for, where to find the number, and a typical example. Tap any next to a box to jump to its explanation.

Mode
How the test times grow from one strip to the next. "Base + fixed increment" adds the same seconds each step (30, 45, 60…). "Base × multiplier" multiplies each step (30, 45, 67.5…). Beginners: keep the first one.
Base time
The shortest time in your test, in seconds. It goes on step 1. Pick a time a bit under what your emulsion maker suggests, like 30 seconds. Your exposure unit is the light box that hardens the emulsion.
Increment / Multiplier
How much longer each step gets. In "fixed increment" mode it is seconds added per step, for example 15. In "multiplier" mode it is a number like 1.5, which means each step is 1.5 times the last one.
Number of steps
How many strips your test screen is split into, from 2 to 12. Six is a common choice. More steps cover a wider range of times.
Current good time
The exposure time that already works for you, in seconds. Get it from a test you ran before, like 60 seconds. Each box below changes one thing from that test.
Light distance you tested with
How far your light was from the screen when you got your good time. Measure from the bulb to the screen with a tape measure, for example 24 inches. Use the same unit for both distance boxes.
Light distance now
How far the light will be from the screen now, for example 30 inches. Use the same unit (inches or cm) as the box above. A light farther away needs more time.
Coats you tested with
How many coats of emulsion were on the screen in your good test. Emulsion is the light-sensitive goo you spread on the mesh with a scoop coater, and one swipe is one coat. A common answer is 2.
Coats now
How many coats you are putting on now, for example 3. More coats make a thicker layer, which needs more light. This math is only a rough guide.
Mesh change
Pick which way your mesh color is changing. Mesh is the fabric stretched on the screen. It comes white or dyed, usually yellow, and dyed mesh needs more light.
Dyed mesh extra
How much extra time dyed mesh needs compared to white, as a percent. There is no single true number, so check your emulsion maker's data sheet or run a test. The 50% default is only a placeholder.
Lamp output lost
How much weaker your light has gotten since your good test, as a percent. Bulbs and tubes fade with age, so 20 means it now gives 20% less light. If you don't know, run a new test instead of guessing.