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Colour quality: CRI, R9 and SDCM explained

Three numbers that decide whether colours look right and whether two luminaires look the same.

CRI (Ra)

The colour rendering index compares how a light source renders eight pastel test colours against a reference source. Ra 80 is the minimum for workplaces; Ra 90 is the norm for retail and hospitality; Ra 95–98 is used in galleries, cosmetics and high-end fashion.

R9

Ra does not include saturated colours. R9 measures saturated red — skin, meat, wood, red fabrics. Two sources with the same Ra can have very different R9 values. For food retail and art, ask for R9 above 50; premium sources exceed 90.

SDCM (MacAdam steps)

SDCM describes how far a luminaire's colour can deviate from its nominal colour temperature. The smaller the number, the more alike luminaires look side by side.

  • ≤ 3 SDCM: differences hard to see — the target for visible rows of downlights and for walls lit by several spotlights.
  • 5 SDCM: differences visible on a white wall.

What to specify

State all three: e.g. 3000 K, CRI ≥ 90, R9 ≥ 50, ≤ 3 SDCM. And order a project from one batch — consistency across batches is never as good as within one.

Related luminaires

Further reading

Three Numbers to Calculate Before You Install Restaurant Lighting Dark tables, bright aisles and spill onto walls usually trace back to spacing, beam angle and aiming angle set in isolation rather than calculated together. Six Track Spotlight Specification Errors That Hurt Retail Sales Six common track spotlight specification mistakes — from chasing efficacy to skipping beam angle simulation — that reduce merchandise appeal and dwell time in retail environments. Beam angles and accent ratios: planning contrast How beam angle, distance and accent ratio work together — and why 24° is the most-specified spotlight in retail.