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Why exposure time is the heart of resin printing
In resin printing, each layer hardens when ultraviolet light shines through the screen for a set time. That time, the exposure time, decides whether the layer cures fully, partially, or too much. Too short, and the layer stays soft, peels off the build plate, or fails to bond to the layer above it. Too long, and fine detail swells shut, small holes fill in, and the print takes far longer than it should. Getting exposure right is the single most important calibration in resin printing, and it changes whenever you change layer height.
The relationship is intuitive: a thicker layer contains more resin to cure, so it needs more light, which means a longer exposure. The calculator scales a known good exposure by the ratio of the new layer height to the old one. If 2.5 seconds works at 0.05 mm layers, then 0.1 mm layers need about 5 seconds by this linear scaling. The calculator also shows a test range twenty percent either side of that figure, because the scaled value is a starting point, not a final answer.
Why linear scaling is only a starting point
Real curing is not perfectly linear. Light is absorbed as it travels through resin, so the bottom of a thick layer receives less light than the top, and doubling the layer height sometimes needs slightly more than double the exposure. Resin colour matters too: dark and heavily pigmented resins block light and need longer exposures than clear resins at the same layer height. Temperature matters as well, since cold resin cures more slowly. These effects are why the resin maker’s datasheet, which lists recommended exposure ranges for common layer heights, always outranks any calculation.
The honest workflow is: calculate, then test. Print a small exposure test piece, such as a calibration matrix with fine holes and thin features, at the calculated time and at the ends of the suggested range. Inspect which version holds detail without breaking. A good exposure shows crisp small holes, clean thin walls, and no soft or tacky surfaces after washing and curing. Pick the middle of the range that passes, not the extreme edge, so normal variation in temperature and resin age does not push you into failure.
A worked example
Suppose your trusted setting is 2.8 seconds at 0.05 mm layers, and you want to print faster at 0.1 mm layers. The calculator gives 5.6 seconds, with a test range of 4.5 to 6.7 seconds. You print test pieces at 4.5, 5.6, and 6.7 seconds. The 4.5 second piece has soft detail and a hole that fills in on one side, suggesting under-exposure. The 6.7 second piece is crisp but its smallest holes are partly closed, suggesting over-exposure. The 5.6 second piece is clean throughout, so you adopt 5.6 seconds for full prints at 0.1 mm.
Now try the reverse: moving from 0.1 mm layers at 5.6 seconds down to 0.03 mm layers for a detailed miniature. The calculator gives 1.68 seconds, with a range of 1.3 to 2.0 seconds. Very short exposures can be unreliable on some printers, because the screen and light source need a minimum time to switch cleanly. If tests at 1.68 seconds show inconsistent curing, use the top of the range or stay at 0.05 mm layers instead. Speed is not worth a failed miniature.
Bottom layers are a different job
Bottom layers, the first few layers that stick the print to the build plate, use much longer exposures than normal layers, often ten to twenty times longer. This is deliberate: they must grip the plate hard enough to survive the peel force of every later layer. Do not scale bottom layer exposure with this calculator. Bottom exposure is set separately in the slicer, and the right value comes from the resin datasheet and from experience with your printer and plate surface. If prints detach from the plate, raise bottom exposure or roughen the plate surface before touching normal exposure.
Also remember that exposure interacts with lift speed and rest time. A print that fails with layers separating may be suffering from peel forces rather than under-exposure, especially on large flat models. Slowing the lift and adding a short rest after each lift lets resin flow back and reduces the force that tears layers apart. Fixing exposure alone will not save a print whose real problem is mechanical.
Frequently asked questions
Can I copy exposure settings from the internet? Only as a starting point. The same resin on a different printer model, with a different light source, needs different exposure. Always test.
Why do my prints succeed in summer and fail in winter? Cold resin cures more slowly and flows worse. Warm the resin and the room to the datasheet temperature range before printing.
Does exposure affect print time much? Yes. Exposure is paid on every single layer, so doubling exposure on a 1,000-layer print adds a large amount of time. That is why finding the lowest reliable exposure matters.
These figures are estimates and general guidance only, not a guaranteed print result. Your resin manufacturer’s datasheet and your printer’s own calibration govern every setting. Handle resin only with ventilation and gloves, exactly as the resin maker’s safety sheet requires. Use the calculator above for a starting point, then prove it with a small test print.
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