Barcode Color: Why Red Bars Won’t Scan (and the Other Color Traps)
Scanners read with red light. Anything that looks like white to that light behaves like a space, no matter how dark it looks to you.
Most barcode scanners illuminate the symbol with red light around 630–670 nm. The sensor sees reflected light: a surface that reflects red light strongly appears bright, and one that absorbs it appears dark. Red ink reflects red light almost completely, so red bars look like white space to the scanner. Yellow, orange and light pink behave the same way.
The rule is contrast at the scanner’s wavelength, not contrast to the human eye. Black bars on white is the safest combination. Dark blue, dark green and dark brown bars on white usually work. White bars on black can work with some scanners but confuses many imagers, and light bars on a dark background are a common source of failure on coloured packaging.
Metallic and transparent substrates add reflection problems. A glossy laminate can bounce the illumination straight back into the sensor, washing out the symbol; a transparent label over a dark product shows the product through the spaces. Use matte white labels and avoid placing the barcode over a reflective or patterned area.
If branding requires colour, keep the bars dark and the background light, check with the actual scanner model used in production, and verify print contrast (PCS) rather than eyeballing it. A simple test is to photograph the label through a red filter: if the bars disappear, the scanner will not see them either.
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