What you are seeing
This fix makes the code scan after dark as well as it scans in daylight. You will test the code in the actual night conditions, then change the size, contrast, placement, and lighting so the camera gets a clean image. Do not judge the fix under office light; judge it where the code will actually be scanned at night.
Likely causes
1.
Too little light for the camera — Quick test: shine a phone torch on the code and see whether it scans.
2.
Weak contrast that daylight masked — Quick test: compare a black-on-white proof with the original in the same dim light.
3.
Glare from a nearby lamp — Quick test: shade the code and change the viewing angle at night.
4.
Code too small for dim-light focusing — Quick test: step closer in the dark and see whether it starts scanning.
5.
Reflective or glossy surface — Quick test: view the code from a slight angle so any reflection moves off the symbol.
Step-by-step fix
Step 1: Go to the real location after dark and test the code on two phones. Note the exact light and angle.
Step 2: Shine a phone torch on the code. If it scans with extra light, low light is confirmed as the cause.
Step 3: Print a larger black-on-white proof and test it in the same night conditions.
Step 4: Move the proof away from lamps and reflections, or switch to matte stock if glare persists.
Step 5: If the location stays dark, add a steady light near the code or move the code to a lit spot.
Step 6: Retest the fixed proof at night on two phones, from the distance people will actually stand.
Step 7: Approve the fix only on the night test, and note the night conditions in the job file.
Putting this into practice
In practice, write the night result into the job file: the location, the light, and the phones you tested. The next person to reprint the code then knows the fix was proven in the dark, not just under office lights. Record the before-and-after behaviour with the job file, so the fix is provable rather than anecdotal. When the same failure appears again, that record tells you whether the old fix held or a new cause appeared.
Common mistakes to avoid
- Testing a night placement under bright office light and calling it fixed.
- Reprinting the full run before a single proof passes, which turns one failure into many.
- Testing on one phone in ideal conditions instead of two phones in the real conditions where a code that scans in daylight but not at night will be used.
- Changing the artwork and the placement at the same time, so you cannot tell which change fixed a code that scans in daylight but not at night.- Skipping the proof test because the change looked small, when small changes cause most repeat failures.
Quick checklist
- The code passes a test in the real night location
- Contrast is strong with dark modules on a light background
- No lamp reflection falls across the symbol at night
- The corrected proof passes on two phones in the real conditions
- The fix is recorded in the job file so the next reprint starts from a proven setup
- Every printed copy is checked against the approved proof
- The proof is retested after any later change to the link, design, or placement
Related tools and guides
- [QR minimum size checker](/qr-minimum-size-checker)
- [QR contrast checker](/qr-contrast-checker)
- [QR print proof checklist](/qr-print-proof-checklist)
- [QR DPI calculator](/qr-dpi-calculator)
- [QR quiet zone calculator](/qr-quiet-zone-calculator)
- [printed QR tester](/printed-qr-tester)
- [QR size calculator](/qr-size-calculator)
