A MacAdam ellipse (measured in SDCM steps) describes how closely fixtures match each other in color. Fewer steps means more consistent color from unit to unit.
| SDCM step | Consistency | Typical use |
|---|---|---|
| 1 to 2 SDCM | Excellent, no visible difference | Premium, museum, retail |
| 3 SDCM | Good, barely perceptible | General commercial |
| 4 to 5 SDCM | Acceptable | Budget, industrial |
| 6 to 7 SDCM | Visible variation | Low-spec applications |
See the Color Temperature Comparison and the CRI Reference Chart.
Understanding MacAdam ellipses (SDCM)
A MacAdam ellipse describes how tightly a batch of LEDs matches in color, measured in SDCM (standard deviation of color matching) “steps.” Fewer steps means tighter consistency: 1–3 SDCM is excellent and used for premium, color-critical work where you can’t have visible tint differences between adjacent fixtures; 3–5 SDCM is good and typical of quality general lighting; beyond about 5–7 steps the differences become noticeable, especially on white walls or in rows of downlights. When many fixtures are seen together, ask for the SDCM rating — a low number is what keeps a ceiling of lights looking uniform rather than patchy.
Where it matters most: rows of downlights, cove and wall-wash runs, and any white surface lit by multiple fixtures — places where even a small tint mismatch is glaring. Where it matters less: isolated fixtures or colored accent lighting. LEDs can also drift slightly in color as they age, so tighter initial binning (low SDCM) plus good thermal design is what keeps an installation looking consistent over its whole life.