Color-matching experiments showed that the scatter of matches around each point on the chromaticity diagram forms an ellipse, varying in size and tilt across the diagram. LED binning borrows the idea: a one-step ellipse is one standard deviation of matching error, and tolerances are stated as 2-, 3- or 4-step ellipses around a target white. The smaller the ellipse, the better fixtures match.
Specify a 2-step MacAdam ellipse for the gallery downlights, the walls are white and any mismatch will show.
Also heard as
- MacAdam ellipses
Do not mix it up with
- SDCM: SDCM is the unit of step size; the MacAdam ellipse is the region drawn using that unit.
Related terms
SDCM
Standard Deviation of Color Matching: the step size used to state how closely light sources match in color.
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'.
Chromaticity diagram
The horseshoe-shaped chart that maps every visible color by its chromaticity coordinates.