A useful exposure time belongs to a documented setup. Change the setup, and the old number becomes a starting hypothesis rather than proof.
How do I find my screen printing exposure time?
Start with the current recommendation for your exact emulsion and exposure unit, then run a physical exposure test on your own coated screen. There is no universal number of seconds: light output, coating, mesh, and processing all change the result. A calculator helps organize or adjust a test; it cannot measure your lamp or prove that a stencil is ready for production.
- No tested baseline yet: Plan a masked step test around the manufacturer's starting time. Inspect washout and retained detail, then narrow the range with another test.
- A physical 21-step wedge result: Calculate a 21-step correction from the exposure used, observed solid step, and the target specified for your emulsion. Confirm the new time on a screen.
- Only lamp distance changed: Estimate the distance adjustment for a point-like source, keeping the rest of the setup fixed. Verify it before using it for a job.
The links select a calculation mode and retain your saved measurements and worksheet notes. Record the emulsion, mesh, light, coating, and test date alongside the result so you can reproduce it.
UV source and lamp geometry
Different lamps deliver different spectra and intensity. For a point-like source, exposure time changes approximately with the square of distance: doubling distance requires about four times the exposure. LED arrays and close, extended sources can depart from the simple model, so confirm the adjusted time.
Emulsion and coating
Emulsion chemistry, sensitization, age, storage, coating count, coating side, and dried stencil thickness all affect the UV dose needed to harden through the mesh. Use the current technical sheet for the exact product, not a generic chart copied from another shop.
Mesh and color
Mesh count, thread diameter, and dyed versus white mesh change how light reaches and scatters through the stencil. A time qualified on one mesh should not silently become the default for every screen.
Film density and contact
The positive must block enough UV in image areas, and it must sit tightly against the stencil. Weak density can fog image areas while poor contact softens edges. Neither problem is reliably fixed by changing time alone.
Development and shop drift
Drying conditions, screen-room light, washout pressure, water temperature, and delays between coating, exposure, and washout can change what you observe. Keep a printed record so a good result can be repeated and a drift can be traced.
Primary overview: Chromaline, Dialing In Exposure
Primary overview: Ulano, How Do I Test Exposure?