# 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, MIT licensed, 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