Surface guide
QR codes on shop windows
A shop window code is read from the pavement, often through glass with strong reflections, so it needs to be 10–30 cm and mounted with reflection in mind. The glass is the problem, not the code.
| Typical scan distance | 1–3 m |
|---|---|
| Minimum code width | 10–30 cm |
| Error correction | M |
Reflections beat everything else
A window reflects the street. A camera pointed at the glass sees the sky, passing cars and the building opposite superimposed on your code. Mitigations, in order of effect:
- Mount the code on the inside of the glass facing out, so it is behind the reflective surface rather than on it — the reflection is then in a different focal plane and the camera can often resolve through it.
- Choose a shaded part of the window, or one facing away from the sun's path.
- Use matt vinyl, never gloss.
- Mount at 1.4–1.6 m, so the reflection of the bright sky is above the code.
Size for the pavement
The scanner is standing outside, typically 1–2 m from the glass. That is 10–20 cm of code. Window decals are usually printed far smaller.
Give it a night job
A window code earns its keep when the shop is shut: opening hours, the menu, online ordering, a booking link. Say so on the decal — "Closed? Order online" outperforms a bare code by a wide margin.