# UV fading and QR codes, which inks survive sunlight

> UV light breaks down inks asymmetrically: colour pigments fade years before carbon black, and dye-based inks fade fastest of all. A QR code fails once fading pushes contrast under roughly 40% luminance difference, long before it looks blank. Expect months from aqueous dye prints, years from solvent and UV-cured inks, decades from engraving.

Source: https://useqr.app/docs/print/uv-fading-and-qr-codes · Last reviewed 2026-08-21 · UseQR is free forever, no signup.

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## What UV actually does to ink

Ultraviolet photons carry enough energy to break the chemical bonds in colourants. Dyes
(single molecules dissolved in the ink) are destroyed molecule by molecule and fade
fastest. Pigments (solid particles), only degrade at their surfaces and last far longer.
And **carbon black is nearly immortal**: it is elemental carbon, with no chromophore bonds
to break, which is why century-old newsprint is still legible while its coloured posters
are ghosts.

The asymmetry is the practical point. In a CMYK print, the colour components fade at
different rates while a carbon-based black holds, so anything printed in mixed colours
drifts in both hue and density. A QR code printed **100% K** starts with the most
lightfast colourant in the workflow: one more reason for the K-only rule in
[CMYK printing](/docs/print/qr-code-in-cmyk-print), and a hard argument against
brand-coloured codes outdoors (see
[brand colour codes that still scan](/docs/design/brand-color-qr-codes-that-still-scan)).

## A QR code fails before it looks faded

The decoder needs roughly a **40% luminance difference** between modules and background.
Fading is gradual contrast erosion: the code passes 60%, 50%, 45% while still looking
"fine" to a passer-by, then crosses the threshold and scans stop, first in bright sun
(where ambient glare eats margin), then everywhere. A visual inspection cannot catch this;
only a scan can. Put outdoor codes on a **quarterly scan schedule**, thirty seconds with
[the scanner](/scan) per site visit.

## Lifetimes by ink system

Realistic outdoor figures for temperate climates, printed dark-on-light with decent
coverage:

| Ink / process | Outdoor life before scan failure |
|---|---|
| Aqueous dye (home inkjet) | **Months**: do not use outdoors |
| Aqueous pigment inkjet | 1–2 years |
| Latex | 3–5 years |
| Solvent / eco-solvent | 3–5 years |
| UV-cured inkjet | 5–7 years |
| Screen print, UV-stable inks | 5–7 years |
| Fired ceramic / enamel | Decades |
| [Engraved or annealed](/docs/print/qr-codes-etched-vs-printed) | Decades: nothing to fade |

Multipliers that shorten every row: south-facing exposure (northern hemisphere), high
altitude, tropical and desert UV indices, halve the estimate for a sun-facing surface in
harsh climates. A **UV overlaminate** typically adds a couple of years and is the cheapest
extension available, the full material stack lives on
[weatherproof QR stickers](/docs/print/weatherproof-qr-code-stickers).

## Design for the fade

- **Oversize by 20–30%** beyond the [ten-to-one rule](/docs/print/the-10-to-1-distance-rule)
  so the code starts with contrast and resolution margin to spend.
- **Error correction Q or H**, consistent with
  [outdoor durability](/docs/print/qr-codes-outdoors-durability) guidance.
- **Print the URL as text** beside the code. Faded-but-legible text is the graceful
  failure; a faded code alone is a dead sign.
- **Plan the refresh cycle at install time.** If the ink system is good for 3–5 years,
  diarise replacement at year 3, and let the quarterly scans catch early failures. A faded
  code in the field is a silent 100% conversion loss. Nobody reports it; they just walk
  away.

## FAQ

### Why did my outdoor QR code stop scanning?
Most likely UV fading. Sunlight bleaches ink until the contrast between modules and background drops below what a decoder needs (around a 40% luminance difference), which happens long before the print looks blank to the eye.

### How long does a printed QR code last in sunlight?
Depends on the ink: aqueous dye prints fail in months, pigment inkjet in 1–2 years, solvent and latex in 3–5, UV-cured in 5–7. Engraved, annealed or fired marks last decades because there is no ink to fade.

### What ink is most UV resistant for QR codes?
Carbon-black-based inks: print the code 100% K. Carbon black is elemental carbon with no bonds for UV to break, so it outlasts every colour pigment in the same print.

### How do I know when to replace a fading QR code?
Scan it, quarterly. Visual inspection cannot judge machine-readable contrast. When scans get slow or need several attempts, contrast is near the threshold, replace before it crosses.

## Try it

- https://useqr.app/url
- https://useqr.app/validate
- https://useqr.app/scan