MacAdam Ellipses and SDCM: What Do They Mean for Your Lighting Project?

Why do some LED installations look uneven?

You have probably seen it before. A row of identical LED fittings installed across a ceiling, yet some panels look slightly warmer, cooler, or even greenish compared to the rest. They are all the same product, the same colour temperature on paper. But the human eye picks up on the mismatch instantly.

This happens because no two LEDs produce exactly the same white light. Tiny manufacturing variations in the chip and phosphor coating mean each LED lands slightly differently on the colour spectrum. The question is how far off it lands, and whether your eyes will notice.

That is where MacAdam ellipses come in.

What is a MacAdam ellipse?

Picture a bullseye on a colour chart. The centre is the target colour, say 4000K daylight white. Each ring outward represents a wider zone of colour deviation. LEDs within the innermost ring look identical to the naked eye. The further out you go, the more obvious the shift.

The industry measures these rings in SDCM steps (Standard Deviation of Colour Matching). A product rated at 3 SDCM means every LED in the batch falls within three rings of the target. Tight. Consistent. Predictable. Our Estrella Pro range falls within this range. 

How many steps before I can see the difference?

1 SDCM . No visible difference. Not achievable in mass production.

2 SDCM . Hardly perceptible, even for trained eyes under controlled conditions. Premium architectural grade.

3 SDCM . The benchmark for quality commercial lighting. Hardly any visible colour difference in real-world installations.

4 SDCM . Slight differences may become noticeable, particularly on white surfaces or when fittings are placed directly side by side.

5+ SDCM . Readily noticeable. Acceptable for outdoor, utility, or industrial spaces but not suitable for quality interiors.

See the Difference SDCM Makes

Select an SDCM step to see how colour consistency changes.












1 SDCM
No visible difference
Every fitting looks identical. This is the theoretical ideal but is not achievable in mass production.
2 SDCM
Hardly perceptible
Almost impossible to detect, even for trained eyes under controlled conditions. The gold standard for premium architectural lighting.
3 SDCM
The commercial sweet spot
Hardly any visible colour difference in real-world installations. This is the benchmark for quality commercial lighting and the standard our products are held to.
4 SDCM
Slight differences may appear
Colour shifts can become noticeable, particularly on white surfaces or when fittings are placed directly side by side. Acceptable for general commercial use.
5+ SDCM
Readily noticeable
Colour variation is visible across the row. Acceptable for outdoor, utility, or industrial spaces but not suitable for quality interiors.

Does this actually matter in practice?

More than most people realise. Colour consistency is not something occupants consciously think about, but it is something they feel. An office with uneven colour across a run of linears feels less considered. A retail space where lighting shifts tone from one bay to the next makes products look inconsistent. A hotel corridor with patchy colour reads as budget.

The lighting can meet every lux level on the spec and still let the design down if colour consistency is off.

Is this the same as CRI?

No, and this is a common mix-up worth clarifying. CRI tells you how accurately a light source renders the colours of objects underneath it. SDCM tells you how consistent the light source itself is from one fitting to the next across a batch. You need both. They measure completely different things.

What should I specify?

For high-end commercial and architectural projects where the lighting is a visible feature of the space: 2 to 3 SDCM (for example, our Flow range.). For standard offices, corridors, and commercial interiors: 3 to 4 SDCM. For back-of-house, industrial, or utility areas: 5 SDCM will do the job. 

Linear Lights in an office building

What SDCM ratings do Linear Lights products achieve?

All of our products are manufactured by Ricoman, where colour consistency is a core part of the production process rather than an afterthought. The Flow+ is rated at MacAdam 3-step, and the Estrella Pro Opal achieves 3-step or better. You will find the SDCM value listed on each product page so you can spec with confidence.

Want help specifying for your next project?

Whether you are comparing products, putting together a schedule, or need photometric data for a lighting design, we are here to help. Get in touch at hello@linearlights.co.uk or call us on 0161 451 5934. We also offer a free lighting design service for commercial projects.

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Related FAQs

What is a good MacAdam ellipse rating for office lighting?

For most office environments, 3 SDCM provides consistent colour quality without significant variation between fittings. For boardrooms, reception areas, or any space where the lighting is a visible design feature, aim for 3 SDCM or better.

Does a higher colour temperature mean worse colour consistency?

Not necessarily. SDCM is determined by the manufacturer's binning process, not by the colour temperature itself. A well-binned 4000K product will be just as consistent as a well-binned 3000K product. Always check the SDCM rating on the datasheet regardless of the colour temperature you are specifying.

Does SDCM get worse over time as LEDs age?

It can. LED colour shifts gradually over its lifetime as the phosphor degrades and the chip temperature changes. A fitting that starts at 3 SDCM may drift further from target over tens of thousands of hours. This is why driver quality and thermal management matter alongside the initial SDCM rating. A well-designed fitting holds its colour point for longer.