What is metamerism
Metamerism occurs when two colours are perceived to be the same under one or more light sources, but in reality have different spectral power distributions. Many factors affect how different or similar the colours are, such as the light source itself, the observer, the viewing conditions, the amount of difference in spectral power distributions and the colour of the fabric.
On example in everyday life is as such. You’re getting dressed in the morning, you throw on a pair of black socks thinking they’re a perfect match, but it’s not until you arrive at work that you realise one of them is navy. That’s metamerism.
Another scenario could be that you are shopping for a new carpet, you choose a lovely honey-coloured one in the store but, when it’s finally laid in your home, you’re shocked to see it’s more of a pallid grey. Again, that’s metamerism.
What’s essentially happening – this phenomenon that is metamerism – is that colours are being viewed in different light sources. So, that carpet viewed under store lighting is going to look different when viewed under the different lights of your own home.
Two samples that appear to match each other under one light source may not match under a different light source if their spectral properties differ. This can be a problem where we want a standard and batch to match under a range of different light sources.
Why is measuring metamerism important?
In industries where colour matching or colour tolerances are vitally important, using materials that are metameric colour matches rather than spectral colour matches can prove to be a major problem.
What do we mean by that? Take the furniture industry as an example. When a sofa is being assembled on the production line, the fabric and exterior components may be manufactured to provide a good colour match under the designer’s office light source.
But no sooner are those colour matches viewed under different light sources, such as artificial daylight, visual differences can occur.
Colour accuracy is a problem for a vast array of industries. Aerospace, food, textiles and many more rely on getting the right colour matches but end up experiencing similar problems.
For lingerie brands, metamerism can be a huge problem. In this case, the vast array of substrates like lace, cotton etc. that must provide a colour match present a severe risk of metamerism.
For brands aiming to make the best quality garments, this makes colour matching an extremely difficult procedure.
A spectral colour match attempts to give two colours the same spectral reflectance characteristic, making them a good metameric match with a low degree of metamerism, thereby reducing the sensitivity of the resulting colour match to changes in lighting, or differences between observers.
Metamerism simply has to be closely monitored. And to manage metamerism during colour production, you have to know what causes it.
What tools can be used to measure metamerism?
We’ve established some of the scenarios where metamerism occurs and why it’s important to avoid it.
But how do we go about that? What are the best ways to measure metamerism?
Technically, we are not trying to measure metamerism but detect it. It can be detected through visual means, by using a light box or Colour Assessment Cabinet (CAC) and through digital means, using a spectrophotometer, which can help predict metamerism when used in conjunction with recipe formulation software. Without standardised assessment environments, visual detection of metamerism can be almost impossible.
For dyers and garment manufacturers, the first step in detecting metamerism typically begins with a spectrophotometer coupled with recipe formulation software.
This allows recipes to be created that are unlikely to be visibly metameric. A light cabinet is then used to visually check samples against the standard and detect any metamerism problems before submission or approval.
What tool is best?
Both light boxes and spectrophotometers can be used individually to measure metamerism, but work best when used together.
Best practice visual and colour assessment calls for both spectrophotometers and light boxes due to their complementary nature.
How does it work?
Spectrophotometer
A spectrophotometer calculates the degree of metamerism by detecting any difference in the spectral reflectance properties of the pair of colour samples. Using the standard numerical representation of the light sources used in the CAC cabinet, a colour software application makes use of the spectral data to calculate the colour difference between samples under the different light sources. If the samples match for one source but do not match for any of the others, then that indicates there is some degree of metamerism between the samples.
Light box
Image: VeriVide CAC60 with samples for visual assessment and detection of metamerism
Using a CAC cabinet enables you to check both the quality of colour match and for any metamerism by providing a range of different standardised light sources within a controlled viewing environment. Each light source has differing spectral properties that will clearly highlight to the observer any metamerism that may be present.
VeriVide Colour Assessment Cabinets have helped scrupulous colour professionals ensure colour and finish consistency for more than 50 years.
VeriVide CACs allow operators to assess samples in optimal viewing environments, providing standardised viewing conditions to international and retailer standards.
