Technical Information

Have you ever walked out of the house wearing two black socks, only to realize at work that one of them was actually navy blue? Awkward, right? That’s exactly what metamerism is all about.

Metamerism occurs when two colors appear to match under one lighting condition but fail to do so when the light changes.

These colors appear consistent under certain lighting conditions, but inconsistent under others.

The image above shows the same dyed wool fabric samples under the U30 fluorescent lamp (top) and the A incandescent bulb (bottom) light sources. Notice how the samples appear to have shifted in color? Of course, this is exactly what manufacturers aim to prevent.

Metamerism is quite common, especially for near-neutral colors such as gray, white, and similar dark tones. As colors become lighter or more saturated, the range of possible metamer matches tends to narrow.

To manage metamerism during the color production process, it’s first necessary to understand the reasons behind its occurrence.

The scientific principle behind metamerism

This phenomenon occurs because the way light sources and objects reflect light gives us our perception of color.

Here are the reflection curves for incandescent light and daylight. Notice that the incandescent lamp has significant energy in the red region, but much less in the blue region. As a result of this increased energy in the red part of the spectrum, objects illuminated by incandescent light appear redder compared to those under daylight, which peaks in the blue region.

Using a spectrophotometer, you can measure objects to see how much light is reflected at each point across the entire visible spectrum.

The resulting reflectance data serves as a "fingerprint" of color, which can be used to generate reflectance curves. Metamerism occurs when hues appear identical under a single, specific lighting condition but actually possess distinct "fingerprints" in reality.

The above figure shows two red reflection curves. Both curves strongly absorb blue light, moderately absorb green light, and reflect red light quite intensely. Notice how the two curves twist relative to each other? When two physical samples exhibit at least three points of intersection like this, they are considered metamer pairs. If objects are metamer pairs, the metamerism phenomenon becomes clearly visible—indeed, although they may sometimes appear to be the same color, they won’t match under all lighting conditions.

What causes metamerism?

When products are assembled using different materials, the phenomenon of metamerism is quite common. Automotive manufacturers are constantly battling this issue. Even if the car body paint is made with pigments distinct from those used for the bumpers and rearview mirrors, and the dyes applied to the interior fabrics have a completely unique "fingerprint" compared to the pigments in the plastic dashboard, the finished vehicle must still match under nearly all types of lighting conditions.

Fluorescent optical brighteners are also common triggers for metamerism in paper, textiles, and liquids. In this process, a chemical substance is added to absorb ultraviolet energy just below the visible spectrum and re-emit that energy at longer wavelengths, making colors appear brighter and whiter. OBA can be challenging to manage and often leads to metamerism issues.

Although these shirts appear to match under daylight, when you turn on ultraviolet light, you’ll notice that each shirt is actually a metamerism pair.

When assembling components from different suppliers, it's crucial to closely monitor metamerism, as variations in pigment formulations or dyeing processes can alter the "fingerprint" of color.

Some tips to avoid metamerism

1. Use a multi-angle spectrophotometer

The spectrophotometer employs three different geometries—0°/45°, spherical, and multi-angle—to achieve the most accurate measurements. To evaluate the metamerism of textured surfaces, you must select the appropriate tool for this task.

• The most common 0°/45° measurement reflects light onto the sample at a fixed angle. While this works well for smooth or matte surfaces, it fails to capture and evaluate the fine details found on glossy and textured surfaces.
• Spherical instruments can measure light reflected from all angles, allowing them to calculate color readings that closely match what the human eye perceives. They are commonly used to measure textured surfaces such as textiles, carpets, and plastics, as well as glossy or mirror-like surfaces—including metallic inks, aluminum foil printing, and other high-gloss finishes.
• Multi-angle devices can observe the color of a sample as it moves back and forth, allowing measurements to be taken from various angles. Today's multi-angle instruments are used for pigments in specialized coatings, as well as for special-effect colors containing additives like mica and pearlescent agents—examples include nail polish and automotive paints.

2. Perform visual assessment under the light box

Proper evaluation can reveal how a product looks under various types of lighting—in every possible setting. It allows for the simulation of lighting colors that closely resemble its eventual environment. For instance, carpet manufacturers can assess how their products appear both in showroom settings and under natural daylight as well as household light bulbs. By using a light box, they can brush the fibers in multiple directions to ensure the color meets their standards.

When the finished product is composed of multiple materials, the light box ensures that the harmony among the components remains consistent under all lighting conditions.

Remember, it’s not uncommon for two different people to look at exactly the same two items and still disagree on whether they match. We call this “observer metamerism.” While color vision tests can help minimize this issue, our eyes are simply human eyes. In fact, if you compare evaluations made at 10 a.m. versus 6 p.m., you might even find yourself questioning your own judgment.