Brighteners: the distribution

The detail behind Optical Brighteners. Every figure here is computed from the M1 and M2 measurements shipped with the library, so anything on this page can be recomputed from the files rather than taken on trust.

FI — how far each sample moves when the UV comes on

ΔE₀₀ between the M1 and the M2 reading of the same patch, across all 4253.

FI	Samples	Share	What it means in practice
under 0.5	1115	26.2%	Effectively unaffected. The ink blocks the paper’s fluorescence.
0.5 – 1.0	784	18.4%	Measurable, below what anyone would notice side by side.
1.0 – 2.0	1337	31.4%	Around one step of the neutral ramp. Visible if you look.
2.0 – 3.0	677	15.9%	Comparable to the distance between neighbouring swatches.
3.0 – 5.0	317	7.4%	A different colour by any working tolerance.
over 5.0	29	0.7%	Unmistakable.

Median 1.15, mean 1.33, 95% of samples below 3.35. 2354 — 55% — move by more than 1.0.

The ten that move most

Code	Name	FI
0P5.79	Palladium	7.34
N.93	Light Pearl Gray	6.09
1R6.71	—	5.97
0B5.92	Alice Blue	5.94
0Y1.88	Birch	5.89
N.90	Frost	5.87
0P4.90	Blanched Lilac	5.83
0G3.92	Pale Ash	5.82

The pattern is not subtle: they are all pale. A light, low-chroma ink lets most of the paper’s fluorescence through, so the sample inherits nearly the whole effect. A dense saturated ink blocks it. Which is why N.93 Light Pearl Gray — the lightest neutral, effectively the unprinted stock — sits near the top of the list, and why a deep blue does not appear on it at all.

The practical reading. If a design lives in pale tints on a brightened stock, the measurement condition is not a technicality — it is most of the difference between what you specified and what arrives.

OBA index — how much brightener reaches each sample

b*(M2) − b*(M1), which is the same quantity QuickChecker reports for a paper. Read against a sample it says how much of the stock’s brightener the ink lets through.

OBA index	Samples	Share
under 0.5	704	16.5%
0.5 – 1.5	823	19.3%
1.5 – 3.0	1250	29.3%
3.0 – 5.0	1324	31.1%
5.0 – 7.0	157	3.7%
over 7.0	1	0.02%

The unprinted stock itself reads 6.46. Nothing printed on it can exceed that by much, and a sample near 0 is one whose ink is opaque to ultraviolet.

The three that read above the paper

Code	Name	What it probably is
0P5.79	Palladium	Either the ink carries a fluorescent pigment of its own, or that sheet was brighter than the reference on the day. Published as measured and flagged, not corrected — both explanations are worth being able to see.
0B5.92	Alice Blue
0P4.90	Blanched Lilac

Recomputing this yourself

Everything above comes from two numbers per sample that ship in the library files: the M1 colorimetry and the M2 colorimetry. FI is the ΔE₀₀ between them; the OBA index is the difference of their b* values. Download CxF with all conditions and both are in front of you.