What it means, when it matters, and what to do about it

Both the MediaLight Pro2 and the Mk2/LX1 are calibrated to D65 — the international standard for daylight white. But calibrating to the same standard doesn't mean two lights are identical. If you have both in the same room, they may not look like a perfect match to each other — and here's why.

The Short Version

D65 is a chromaticity target — a single point on a color chart. Many different spectral profiles can land on that same point. The Pro2 and Mk2/LX1 both hit D65, but they take different spectral paths to get there. To a colorimeter, they measure identically. To your eye, especially when viewed side by side, they may look slightly different — because your eye is not a colorimeter.

What Is Metameric Failure?

Metamerism describes two light sources (or colors) that appear identical under one set of conditions but differ under another. It's a fundamental property of human color vision, not a product defect. Our eyes have three types of cone cells, and what we perceive as "color" is really just the ratio of signals between them. Two very different spectral profiles can produce the same cone response — making them look identical in isolation — but reveal their differences when placed side by side or when the viewing context changes.

For bias lighting, this is particularly relevant. The glow behind your display is always in your peripheral vision. If two lights with different spectral profiles are both visible at the same time — behind two displays, or as bias light and room fill — your visual system will detect the mismatch even if both measure as D65.

Key concept: D65 is a chromaticity point, not a spectral fingerprint. The Pro2 and Mk2/LX1 both land on that point, but via different spectral paths. Viewed in isolation, each looks correct. Viewed together, the difference between them may be visible.

When Does This Actually Matter?

Single display, one product only — No issue
Using either the Pro2 or Mk2/LX1 alone is perfectly fine. There's nothing to mismatch against.

Two displays in the same room, each with a different product — Caution
Both bias light halos will be visible simultaneously. Even if both measure D65, they may look slightly different from each other — which can be distracting or undermine reference accuracy.

Bias lighting + room ambient fill using different products — Caution
If your bias light and your room fill are from different product families, both sources will be in your field of view at the same time. The mismatch may be subtle or obvious depending on your sensitivity and room layout.

Critical color grading environment — High concern
In a reference grading environment, any visible mismatch between light sources is a problem. Use one product family throughout — both as bias light and as any supplemental room lighting.

Home theater, gaming, general viewing — No issue
For non-critical viewing, any perceptual difference between the two products is unlikely to be noticeable or meaningful.

Why Do the Pro2 and Mk2/LX1 Have Different SPDs?

The two products use different LED technologies optimized for different priorities. The Pro2 is built around a phosphor-converted white LED with a CRI 99 spectral profile — very smooth across the visible spectrum, with particular strength in the red channel. The Mk2/LX1 uses a different LED architecture, also high CRI (98), optimized for a slightly different balance of spectral power.

Both are exceptional products. Their SPD difference is not a flaw — it reflects different engineering trade-offs. But because human vision is sensitive to spectral differences even when chromaticity matches, placing them in the same field of view can reveal those differences.

What Should You Do?

If both products will be visible at the same time — whether as bias lighting on two separate displays, or as bias light and room fill — we recommend choosing one product family and using it consistently. Either the Pro2 or the Mk2/LX1 will serve you extremely well. Mixing them introduces a visible variable that's worth eliminating if consistency matters to you.

If the products are in separate rooms or used for entirely different purposes, there's no issue. The concern is specifically about simultaneous visibility in the same environment.

If you're unsure whether your setup is affected, we're happy to help you think it through before your order ships. We'd rather you get the right product than make the wrong sale.

Questions?

Email us via our contact form. We review every order personally and are happy to talk through your specific setup.