Colour Consistency in LED Strip: SDCM and Binning
Why two 3000 K strips can look different, what SDCM 3 means in practice, and how project-level bin control prevents a visible tint step in a continuous run.
HFY Applications Engineering · Published September 29, 2026 · 3 min read
Colour consistency is controlled by binning: measuring each production reel's chromaticity and sorting it into a 3-step MacAdam ellipse, then shipping reels from one bin and one production lot together. Two reels both labelled 3000 K can sit up to 7 SDCM apart if they come from different bins, which is visibly two different whites on an adjacent run.
Key points
- SDCM is a distance from a nominal colour point, measured in just-noticeable-difference steps.
- SDCM 3 is undetectable side by side; SDCM 5 shows as a tint step; SDCM 7 reads as two whites.
- Binning is per reel; project consistency requires lot control on top of binning.
- Δuv is the number to ask for when matching an existing installation.
What “3000 K” actually permits
The 3000 K point on the blackbody locus is a single coordinate. A manufacturer’s production spread around it is not a point but a cloud, and the industry defines that cloud in MacAdam ellipse steps.
| Bin | Practical perception | Where it is acceptable |
|---|---|---|
| SDCM 2 | Not detectable | Multi-phase projects, adjacent facades |
| SDCM 3 | Not detectable side by side | Continuous runs, one elevation |
| SDCM 5 | Detectable on close comparison | Separate rooms, non-adjacent runs |
| SDCM 7 | Reads as two different whites | Single-room decorative use only |
Two reels both labelled 3000 K, one at the top of an SDCM 7 bin and one at the bottom, differ by up to 0.008 in Δuv. On a white ceiling that is unmistakable.
The failure mode you will actually meet
A cove runs 42 m around a lobby. The installer uses six reels; five come from one production lot, the sixth from stock left over from a previous job. The strip lights up, and from the floor there is a step in the light at metre 35 that the client sees immediately.
The cause is not a defective reel. It is that “3000 K” was the only thing specified, so any 3000 K reel was considered interchangeable. The fix is a project-level specification:
One production lot for the whole elevation, SDCM ≤ 3, bin code recorded on each reel label, 10% spare from the same lot.
That sentence costs 4–8% more and prevents a re-visit.
How binning works in production
- The reel is stabilised for 30 minutes at 25 ± 1 °C.
- It is measured on a spectroradiometer in an integrating sphere.
- Chromaticity (x, y), flux and forward voltage are recorded.
- The reel is assigned a bin code covering all three.
- Reels of the same bin are packed together and labelled.
The flux and voltage bins matter as much as colour. Two parallel runs fed from one driver will share current according to their forward voltage: a 0.4 V difference between reels produces a visible brightness difference even when the colour matches. That is why a proper bin code covers three parameters, not one.
Matching an existing installation
The question “can you match a strip installed three years ago?” is answered with Δuv, not with CCT. Send the reel label or a photograph of it. If the bin record is still available, the match is exact. If not, the nearest current bin is quoted with its measured Δuv against the original, and the decision becomes a number the designer can judge rather than a promise.
We hold bin records for five years for this reason. The colour consistency capability page describes the measurement setup, and how to specify LED strip puts SDCM in the context of the other five numbers that matter.
This article describes general manufacturing practice for machined and fabricated components. It is not a substitute for a drawing-specific engineering review — tolerances, material selection and process capability depend on the individual part.