Standard Deviation of Color Matching, the unit behind MacAdam ellipse tolerances. A source within 1 SDCM of a target is indistinguishable to nearly everyone; 2 to 3 SDCM differences are barely visible when sources sit side by side; 5 or more are obvious. Product sheets quote color consistency as a number of SDCM steps, and tighter values cost more because fewer LEDs from production qualify.
Datasheet says 3 SDCM but the samples on the mock-up wall look like 5, ask the rep for the bin data.
A step count only matters when sources are seen together: a 4-step mismatch is invisible across a hallway and obvious in a row of downlights washing one wall.
Also heard as
- MacAdam step
- step
Related terms
MacAdam ellipse
A small oval around a target color on a chromaticity chart, inside which color shifts go unnoticed by most viewers.
Binning
Sorting LEDs after manufacture into groups with matching color, brightness and voltage.
Chromaticity
Where a light's color sits on a color map once brightness is set aside, given as coordinates such as x, y or u', v'.
CCT
Correlated Color Temperature: the warm-to-cool appearance of white light, stated in kelvin.