Understanding the RAL contrast tool

This tool helps you quickly check if two RAL shades (or a reference color against the entire color chart) are contrasting enough to be clearly visible to all people, especially those with visual impairment, reduced sensitivity to light, or in emergency/stress situations.

This is particularly useful for signage, doors, walls, guide strips, switches, handles, stair nosings or any important element in an accessible building.

Why do we display “luminance”? Luminance (value between 0 and 1) measures the brightness perceived by the human eye.

• 0 = absolute black
• 1 = absolute white

It's not just an average of the RGB values: the eye sees much more green than red or blue, so luminance truly reflects how we perceive brightness. Two colors can have similar RGB values but appear very different (e.g., bright yellow vs. dark purple). It's this luminance that allows for a realistic calculation of contrast, especially indoors with varying lighting.

How is contrast calculated? The officially recognized formula (WCAG) is used: (brightest luminance + 0.05) / (darkest luminance + 0.05) → Result = ratio (e.g., 5.8:1). The higher the number, the more easily the two colors are distinguished.

Interpretation of the results

WCAG (reference for digital design and accessibility)

• AAA (dark green): ≥ 7:1 → Excellent, very safe
• AA (light green): ≥ 4.5:1 → Minimum compliant level (most common)
• Failure (red): < 4.5:1 → Risk of confusion, to be avoided for important elements

SIA 500 (Swiss standard for barrier-free construction) SIA 500 requires sufficient contrast for safety and orientation elements (doors, tactile paving, handles, stair nosings, etc.). In practice (and as an approximation with our calculation):

• ≥ 6:1 → Very good for danger/warning (stair nosing, strips)
• ≥ 4:1 → Sufficient for priority I (small objects: handles, switches, controls)
• ≥ 2:1 → Sufficient for priority II (large areas: walls vs floor, general orientation)
• < 2:1 → Often insufficient, needs to be physically verified

Important: For projects subject to SIA 500 control or certification, actual measurements on samples (using a luminance photometer) remain the absolute reference. This tool is an excellent initial quick filter, but it does not replace on-site verification.

All information is indicative and does not constitute a commitment on the part of Riviera Couleurs.