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Colour rendering and CRI in luminaire selection

Short answer

Colour rendering is the ability to show true colours; poor CRI leads to errors. CRI (0–100) measures it; select luminaires with CRI ≥90 for colour-critical tasks (hospitals, printing), ≥80 for offices, and lower for warehouses, balancing task needs with efficacy.

Why is color rendering important and how CRI help in selecting luminaries?

Colour rendering is the ability of a light source to show the true colours of objects compared with a reference source (daylight or an incandescent lamp). It is measured by the Colour Rendering Index (CRI or Ra) on a scale of 0–100; 100 means colours look exactly as under the reference source.

Why colour rendering is important

  • Correct identification: colour-coded wires, pipes, safety signs, and medicines must be recognised correctly; poor CRI can lead to errors and accidents.
  • Quality control: printing, textile, paint, food grading and hospital work need accurate judgement of colour.
  • Visual comfort and appearance: skin tones, goods in shops and interiors look natural and pleasant under high-CRI light.
  • Productivity: better colour contrast reduces eye strain and mistakes.

How CRI helps in selecting luminaires

CRI (Ra)QualityTypical sourcesSuitable application
90–100ExcellentHalogen, high-CRI LEDColour matching, art galleries, hospitals
80–89GoodLED, triphosphor fluorescentOffices, schools, shops, homes
60–79ModerateMetal halide, standard fluorescentIndustrial halls, sports areas
20–59PoorMercury vapour, HPSWarehouses, street lighting
< 20Very poorLow-pressure sodiumRoads, security lighting

So the designer first fixes the minimum CRI the task needs (e.g. Ra ≥ 80 for offices as per EN 12464 / IS 3646, Ra ≥ 90 for colour inspection), then chooses among the lamps meeting it the one with the highest efficacy and suitable colour temperature.

✓ Answer checked by Claude Opus 5.5 (high effort)

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