Resin Exposure Settings

What exposure is

A resin printer builds each layer by lighting the shape of that layer through the film at the bottom of the vat. Exposure time is how long that light stays on. Too little and features do not form; too much and they swell. Prusa's calibration guide describes overexposed test letters and digits as too thick and melting together.

Slicers keep two exposure settings:

• Normal layer exposure (Prusa calls it "Exposure time"): every layer after the first few.
• First or bottom layer exposure (Prusa: "Initial Exposure time"): the first layers, which have to bond to the build plate. Phrozen notes that adding exposure helps a model adhere to the build plate.

How wrong exposure looks

Underexposed	Overexposed
Thin features missing or broken (Prusa, Phrozen)	Letters and digits thicken and melt together (Prusa)
Small pillars missing or barely there (Phrozen)	Pillars look larger, gaps uneven (Phrozen)
Thin lines faint or gone (Phrozen)	Separate panels or lines merge; small holes fill in (Phrozen)

Prusa adds a caution: not every resin can print very fine detail, so a blurry detail does not always mean underexposure. Compare against the test model's intended geometry before you change anything.

Exposure is also a printer safety setting. Prusa says to always use the recommended exposure times for your resin, and warns that wrong times can damage the printer. Do not set a long exposure "just to be safe" without a reason.

What changes the right value

• The resin. Every formulation and color cures at its own rate. This is the biggest factor, and the reason bundled files need adjusting: Prusa's SL1S example files are prepared for one Prusa resin, and Prusa says to adjust exposure for any other.
• The printer. A profile for one printer is not a profile for another, even with the same resin. Prusa even gives different calibration steps for its SL1 and SL1S.
• Layer height. Exposure is tied to layer height: Prusa provides calibration objects and resin profiles per layer height, and its procedure has you pick a base resin preset at the layer height you calibrated. See Choosing a Layer Height.
• Temperature. Cold resin flows less. For one Elegoo printer and resin pair in cold weather, Elegoo suggests raising bottom exposure by 5 seconds and normal exposure by 0.5 seconds Maker spec, along with lift changes. That is Elegoo's adjustment for its Saturn 3 Ultra and one of its resins, not a general rule; fix the room temperature first (Setup).
• The film. Prusa's calibration guide asks for a nearly new film, because scratches or dirt affect the light.

Finding your value

1. Start from the resin maker's profile for your printer and layer height Starting point. If your printer is not listed, ask the resin maker; do not borrow another printer's number.
2. Print an exposure test. A calibration model prints several copies or features at different exposures. Prusa's printers can print one object per exposure step and mark each with its exposure time. The resin exposure test lesson walks through printing and reading one.
3. Search wide, then narrow. For an unfamiliar resin, Prusa suggests starting with a 1 second step on the SL1S or 3 seconds on the SL1 Starting point, then repeating with a finer step around the best result.
4. Pick the exposure where every feature forms and nothing merges, checking against both columns of the table above.
5. Decide on a margin for real models. Phrozen recommends raising the layer exposure from its XP Finder test by at least 10 percent for the actual model, and up to 20 percent for models larger than 12 cm Rule of thumb, to help adhesion and full cure. That is Phrozen's advice for its test; other makers may not add a margin.
6. Save it as a new profile. In PrusaSlicer, Prusa's steps are to select a base resin at your layer height, save it under a new name, and set "Initial Exposure time" and "Exposure time" to your values.

Change one thing at a time

When a print fails, exposure is not always the cause. Layers separating, prints sticking to the film and supports pulling off can come from exposure, from orientation and supports, or from a cold room. Change one variable, print the test again, and compare. For specific symptoms, see Resin Layers Separating, Print Stuck to the Film and Orientation and Supports.