TLDR: M0 M1 M2 measurement conditions tell you how a color-measuring instrument handles ultraviolet energy when it reads a printed sample. M0 has unspecified UV content, M1 controls the illumination to better represent D50 behavior, and M2 excludes UV. The same sheet can therefore produce different Lab and Delta E results—especially when its paper contains fluorescent optical brightening agents. None of these modes changes the artwork or print; they change how the sample is measured.
If a proof passes one report but appears to fail another, do not assume the ink changed. First check whether both reports used the same measurement condition. M0 M1 M2 measurement conditions are part of ISO 13655, the graphic-arts standard covering spectral measurement and colorimetric computation. ISO identifies the current supplied edition as ISO 13655:2017, published in 2017 and confirmed in 2022. View the ISO 13655 standard record
Why one printed sheet can produce different readings
Many very white papers contain optical brightening agents, commonly shortened to OBAs. These substances absorb ultraviolet energy and re-emit some of it as visible light, generally adding a bluish contribution that makes the paper appear brighter or less yellow under lighting with sufficient UV.
A spectrophotometer illuminates the sample and measures the light returned from it. If one measurement includes UV energy and another blocks it, the OBA-containing sheet does not respond in the same way. Its measured paper white can shift, and that shift can affect the reported values of printed colors sitting on the paper. The ICC and ISO/TC 130 both identify fluorescence as a central reason that measurement conditions can produce different spectral and CIELAB interpretations of the same sample.
Think of a white shirt under daylight and then under a UV lamp. The material has not been repainted, but fluorescent substances respond differently to the light. Paper whiteners create a more controlled and less dramatic version of the same underlying issue.
The effect is not equal on every stock. A warm, unbrightened paper may show a relatively small difference between UV-included and UV-excluded readings. A highly brightened stock can show a more meaningful difference. That is why the measurement condition belongs in the report rather than being treated as an invisible instrument preference.
M0, M1, and M2 measurement conditions compared
| Condition | Treatment of UV | Practical meaning |
|---|---|---|
| M0 | UV content is unspecified | A legacy-compatible condition that may vary between instrument light sources, particularly when fluorescent materials are involved. |
| M1 | Controlled to represent D50 behavior | Designed to improve alignment between measurement and D50-oriented graphic-arts workflows, including fluorescent substrates. |
| M2 | UV is excluded | Removes the fluorescence contribution stimulated by UV, supporting workflows that intentionally require UV-cut data. |
| M3 | Uses polarization | Reduces gloss-related effects and is more specialized than the UV-focused M0, M1, and M2 comparison. |
These definitions follow the International Color Consortium’s explanation of ISO 13655 measurement conditions. The ICC notes that M1 and M2 normally produce different results for fluorescent samples and recommends specifying the condition when characterization data is exchanged. Read the ICC measurement-condition white paper
M0: UV is not tightly defined
M0 does not require a specific UV relationship in the instrument illumination. Two instruments operating in M0 can therefore stimulate an optical brightener differently. This matters less when the sample is nonfluorescent, but it can complicate comparisons across instruments, paper stocks, or older characterization data.
M0 data is not automatically wrong or unusable. It may be the documented basis of an existing press target, profile, customer standard, or historical workflow. The practical rule is to compare it with compatible M0 data rather than silently treating it as interchangeable with M1 or M2.
M1: controlled UV behavior for D50 workflows
M1 is intended to model the fluorescent response associated with standard D50 illumination more consistently. D50 is a standardized daylight-like illuminant used in graphic-arts color evaluation; it is not simply any lamp marketed as daylight.
M1 often matters when a workflow uses brightened paper and aims to coordinate instrument readings, characterization data, proofs, and D50 viewing. It is not universally superior. It is appropriate when the reference data, output profile, proofing target, measurement equipment, and evaluation workflow are designed around it.
M2: UV-cut measurement
M2 excludes UV from the measurement illumination. With no UV stimulation, the reading intentionally leaves out the fluorescence contribution from optical brighteners. This can be useful when a specification calls for UV-cut data, when comparing materials without their UV-stimulated response, or when maintaining compatibility with an established M2 workflow.
M2 does not reveal the one “true” color of the sheet. A brightened sheet may still look different under illumination that contains UV because human viewers can see the resulting fluorescence. M2 answers a defined measurement question; it does not override the viewing environment.
Why Lab and Delta E reports need an M condition
Lab describes a color using lightness and two opponent color axes. Delta E summarizes the numerical difference between two color measurements. Both are useful, but the numbers only make sense in context.
Suppose a printer measures a pale brand color on a bright white card stock using M1, while the customer’s reference was recorded in M2. A reported difference may partly reflect how the two measurements treated paper fluorescence rather than an equivalent comparison of ink reproduction. Recalculating Delta E cannot repair incompatible source measurements.
Before deciding whether a difference is acceptable, confirm that the reference and sample used compatible conditions. The measurement condition is not the only variable: instrument geometry, backing material, selected illuminant and observer, calculation method, sample condition, and measurement procedure can also matter. Matching the M label alone does not guarantee identical results or visual agreement.
For more help interpreting the resulting number, see TutorArt’s practical guide to Delta E in printing. A tolerance should be connected to the object, color, process, and viewing purpose rather than treated as a universal pass-or-fail score.
What creators and print buyers should ask
Most artists ordering posters, stickers, cards, or invitations will not select an M condition in a design application. It is an instrument and production-workflow choice, not a Photoshop color mode or PDF export setting. The creator’s job is to make the matching target unambiguous and ask how it will be evaluated.
When color matching is important, ask the printer or proofing provider to document:
- The ISO 13655 measurement condition used for the reference and production sample: M0, M1, M2, or another documented condition.
- Whether the target is a supplied physical sample, an approved contract proof, named brand-color specification, ICC-based proof, or best-effort visual match.
- The paper or substrate used for the proof and final production, including whether a stock substitution is expected.
- The viewing setup used for visual approval, especially when optical brighteners are present.
- The color-difference formula and tolerance, if a numerical acceptance limit is part of the job.
- Whether coatings, laminates, varnishes, or other finishes are measured before or after application.
- Which proof controls the decision if the instrument report and visual assessment appear to disagree.
If you are sending a job to a commercial printing provider such as Printiverse, put critical color expectations in the project notes and retain the approved proof or reference. Do not assume that a request for “accurate color” communicates a measurement condition, substrate, tolerance, or viewing setup.
Color measurement becomes useful only after the underlying file is prepared correctly. Resolution, bleed, trim, color spaces, and suitable file formats remain separate concerns; TutorArt’s guide to print design basics and file preparation covers that broader handoff.
What M modes do not solve
A documented measurement condition makes reports more interpretable, but it does not make every part of a printing workflow equivalent. It cannot compensate for an uncalibrated monitor, colors outside the printing process’s gamut, a changed ink set, a substituted stock, or a finish that alters gloss and contrast.
It also cannot ensure that a print looks identical in every room. A brightened paper may appear cooler under lighting with meaningful UV and warmer under lighting with little UV. Dark ink areas may hide paper fluorescence differently from highlights. Lamination and surface texture can change perceived saturation or glare even when the underlying ink values remain unchanged.
Measurement should therefore support visual assessment rather than replace it. ISO/TC 130 guidance explicitly notes that instrumental measurement does not replace final human evaluation of complex printed images. For artwork with delicate neutrals, skin tones, deep shadows, or large areas of paper white, inspect an appropriate proof under a controlled viewing condition as well as reviewing the numbers.
A simple decision framework
- Identify the target. Decide whether you are matching a file, physical sample, proof, brand specification, or previous production run.
- Keep the data compatible. Use the measurement condition required by the target or specification rather than choosing an M mode in isolation.
- Control the substrate. Record the actual stock because its whiteness and fluorescence can influence both measurement and appearance.
- Separate numerical and visual approval. A color report answers a defined measurement question; a proof shows how the complete image behaves on a physical surface.
- Document the result. Save the proof identity, stock, finish, measurement condition, tolerance method, and approval decision for a future reprint.
Common questions
Can an M0 report be compared with an M1 report?
You can inspect both, but you should not assume their Lab values are directly equivalent. The difference may be small on a nonfluorescent sample and larger on an OBA-containing paper. For a formal comparison, remeasure the reference and sample under a compatible documented condition.
Is M1 always the best option?
No. M1 is useful in D50-oriented workflows and with fluorescent substrates, but the correct condition is the one required by the relevant specification, reference data, profile, proofing system, and production agreement.
Do these conditions alter the printed product?
No. Switching an instrument from M1 to M2 changes the illumination used to measure the sample. It does not add ink, remove optical brighteners, convert the artwork, or modify the physical print.
What is M3?
M3 is a polarized measurement condition used to reduce surface-reflection and gloss effects. It is worth recognizing, but it addresses a different measurement concern and is less central to the question of how UV stimulates paper whiteners.
The practical takeaway
M0, M1, and M2 are not quality grades. They are defined ways of illuminating a sample during measurement. Paper whiteners make the distinction visible because their fluorescence depends on UV energy.
When a color report matters, ask which condition produced it and whether the reference used the same condition. Then confirm the substrate, proof, viewing setup, formula, and tolerance. That small amount of documentation helps separate a genuine printing difference from a measurement mismatch—and gives both creator and printer a clearer target for the next run.