How MacAdam 3-Step Binning Works in LED Sourcing
MacAdam ellipses describe how much two colors can differ before an average observer notices. In LED sourcing, the MacAdam step (SDCM) is the binning tolerance: a “3-step” LED keeps every unit within three MacAdam ellipses of the target chromaticity. For professional lighting, this is the difference between a consistent fixture fleet and a rainbow of slightly different whites.
The Physics Behind the Ellipse
Human color discrimination is not uniform across the CIE diagram — we are far more sensitive to small shifts along certain directions (notably toward blue/yellow). MacAdam's experiments defined elliptical regions around a target color: one step is the just-noticeable difference for an average observer under controlled viewing.
- 1 step: virtually indistinguishable from target — expensive, used in calibration labs
- 2 steps: perceptible only in direct side-by-side comparison
- 3 steps: the professional baseline — side-by-side consistency in installed fixtures
- 5–7+ steps: visible color differences between units — common in commodity LEDs
What Binning Actually Controls
LED manufacturing has inherent variation: phosphor coating thickness, die wavelength, encapsulation. Binning sorts production output by measured chromaticity into tolerance boxes on the CIE diagram. What you buy is a binning policy:
| Binning | Visible result in a two-fixture installation | Typical cost impact |
|---|---|---|
| 3-step MacAdam | Whites look the same | Reference |
| 5-step | One unit slightly pink/green next to the other | ~5–10% lower |
| 7-step | Clearly different whites, customer complaints | 10–15% lower |
Why It Matters More in Tunable White
In a tunable white COB LED, two channels (warm and cool) must each hold their bin and their relative output calibration. If the warm channel sits at one edge of its 3-step bin and the cool channel at the opposite edge, mid-range CCT mixes inherit that chromaticity error. Quality TW platforms therefore bin both channels consistently and calibrate the mixing curve per production batch.
Binning Beyond White: Color COB
For RGB/RGBW COB modules, the same principle applies to colored dies: red die wavelength bins (e.g. 620–625nm vs 625–630nm) determine whether two fixtures produce the same saturated red. Multi-channel engines need cross-channel binning discipline to keep every fixture's gamut identical.
Sourcing Checklist
- Ask for the binning structure in writing (steps, sub-bins, per-channel for TW/color)
- Request per-batch chromaticity reports, not just datasheet values
- For TW, ask how the mixing curve is calibrated and whether Duv is controlled across the range
- For fleets, order one bin/lot per project — and hold spares from the same lot
TYANSHINE specifies MacAdam 3-step binning across its TW COB platforms — details in the Tunable White COB LED specifications. Related: What Is Tunable White COB LED?