Why There Is No Universal Screen Exposure Time
Screen exposure must be tested on the actual emulsion, mesh/coating, film and light source. A step test around a baseline is more defensible than copying another shop’s number because multiple darkroom variables change the required dose.
Use the numbers from your actual job
The guide explains the decision; the linked calculator gives you the value for your own file or production assumptions.
Exposure time is setup-dependent
Specialist screen-printing guidance identifies mesh count, stencil thickness, humidity, bulb strength, emulsion and other variables as reasons no single exposure time works everywhere.
Test a range instead of guessing one number
Use a step-wedge or suitable exposure test image and create several controlled times around your current baseline. Keep everything else constant so the result tells you something about exposure rather than a simultaneous process change.
Record the successful combination
Once a step resolves detail and produces a durable stencil, record the emulsion batch/type, coating method, mesh, light source/distance and exposure time. Re-test after changing a variable rather than assuming the old time remains correct.
Practical answer
Screen exposure must be tested on the actual emulsion, mesh/coating, film and light source. A step test around a baseline is more defensible than copying another shop’s number because multiple darkroom variables change the required dose.
When the decision affects a paid print run, book upload, client order or expensive material, keep the calculation with the job notes and verify any external specification again immediately before production.