1. Reverse Printing
If the graphic is applied to the inside face of the glass and viewed from outside, the artwork must be mirrored so it reads correctly through the pane. Many scanners can decode a mirrored code, but do not rely on it. Confirm by scanning from the viewing side with a [QR scanner](/qr-scanner). Generate your codes using our [URL QR code generator](/url-qr-code-generator) before mirroring for print.
2. Background Problem
Window codes lose contrast because the background changes with daylight and what is behind the glass. Use an opaque white backing panel behind the code, or print a solid light patch. Use our [QR size calculator](/qr-size-calculator) to ensure adequate module size for challenging lighting conditions.
3. Glare
Reflections from sun and street lights can wash out modules. Prefer matte film and angle the placement away from direct reflections. Test at different times of day using our [printed QR tester](/printed-qr-tester) methodology. Follow our [QR placement guide](/qr-placement-guide) for optimal positioning that minimizes glare. Consider using our [error correction simulator](/error-correction-simulator) to plan for partial obstruction from reflections.
4. Height and Safety
Place it at a comfortable standing height, away from traffic where people might step off the pavement to scan. Create trackable URLs with our [UTM builder](/utm-builder) to measure window signage effectiveness.
Putting this into practice
Start with the smallest real test you can run. Generate the code, print it at the exact size you plan to use, and scan it with two different phones in the lighting where it will live. Check that the destination page loads quickly on a mobile connection and that the call to action next to the code tells people what they will get. If anything feels slow or unclear, fix it before you print a full batch, because reprints cost more than a short test. Keep a note of the size, material, and placement that worked so the next batch starts from a proven setup.
Common mistakes to avoid
The most common mistakes are easy to avoid once you know them. Long payloads make modules tiny, low contrast makes edges hard to read, and text placed too close to the border eats the quiet zone the scanner needs. Covering a corner finder pattern with a logo or a sticker breaks detection entirely, and a code placed behind glare or on a curved surface fails even when the print is perfect. Review each of these points on a proof copy, and treat any failure as a reason to adjust the design rather than a reason to blame the scanner.
Quick checklist
- Keep the payload as short as practical so modules stay large.
- Keep dark modules on a light background with strong contrast.
- Leave a clear quiet zone on all four sides of the symbol.
- Test the printed code at the real viewing distance and lighting.
- Confirm the destination page loads fast on a phone.
- Recheck the code after any change to the link, design, or placement.
