Window Decals: Scanning Through Glass
Window decals on shopfronts are scanned by pedestrians standing 1 to 2 meters away, often through the glass itself or from an oblique angle. Glass adds reflections, the street adds glare, and the viewer is usually in motion — walking past, glancing over, deciding in two seconds whether to stop. Everything about this environment argues for generous sizing and ruthless contrast.
The 10:1 Rule of Thumb
At 1.5 m viewing distance, the rule of thumb gives 150 mm; in practice, 100–150 mm works for storefront decals because pedestrians typically stop and step closer once interested. Size for 1.5 m as the working distance, and treat anything smaller than 100 mm as a close-range-only code that will fail for passersby. If the decal must be scanned through the glass rather than off its surface, add another 20% — the glass costs you contrast you have to buy back with size.
Recommended Size
Print at 120 × 120 mm (about 4.7 inches). On a standard shopfront, this is clearly visible without dominating the window display, and it survives the contrast losses of glass, glare, and oblique angles. For decals on doors that people approach closely, 100 mm is acceptable; for upper-window placements viewed from across the sidewalk, go to 150 mm.
Substrate and Printing
Decals use perforated one-way-vision vinyl, static-cling film, or adhesive vinyl, printed by UV or latex large-format printers. On clear films, a white ink underbase behind the code is essential — without it, the bright shop interior shows straight through the code and contrast collapses to nothing. Decide the application side before printing: inside-glass decals that read correctly from outside must be reverse-printed (mirror image), a mistake that is expensive to discover after installation.
Placement and Practical Tips
- Apply at waist-to-chest height where pedestrians naturally look; ankle-height codes get ignored and above-head codes get neck strain instead of scans.
- Avoid placing the code where interior spotlights reflect directly into the camera; visit at midday when sun glare is worst and test then.
- Perforated one-way-vision vinyl (the kind with tiny holes for see-through from inside) can interfere with fine modules — keep the code off perforated areas or size up to compensate.
- Pair the code with a reason: opening hours, today's offer, the booking link. A naked code on a window is easy to walk past.
- Tinted or low-e glass darkens everything, including your contrast — test through the actual installed glass.
Common Mistakes
- Clear static-cling film with no white underbase — the code becomes a ghost of the interior and scans only in perfect conditions.
- Mounting at ankle height or above head height instead of the natural sightline.
- Forgetting that the setting sun turns a west-facing window into a mirror for an hour every evening.
- Printing inside/outside orientation backwards and discovering the code reads mirrored from the street.