What is Metamerism?

What is Metamerism?

Posted Last Sunday by Donna Creek

Have you ever experienced looking at a garment/material colour under incandescent light to realise in daylight the colour is rather different, what you will have experienced is Metamerism. We all experience this in our everyday lives, so what’s the cause behind it?

Metamerism is commonly defined as “two objects which match when illuminated by one light source and then do not match when illuminated by a different light source.”

Incandescent light bulbs contain relatively little light in shorter blue wavelengths, making it more difficult to distinguish blue colours under these lighting conditions. Fluorescent illumination in the kitchen emits more short-wavelength light, and thus the dark blue can be more easily distinguished from black. In incandescent light, the socks are a “metameric match;” in fluorescent light, they do not match.

In actuality, there are several types of metamerism, including sample, illuminant, observer, and geometric.

  • Illuminant metamerism – witnessed when you have a number of spectrally matched (exactly the same) samples, but when each is independently, yet simultaneously illuminated and viewed under lights whose spectral power distributions differ.
  • Sample metamarism – when two color samples appear to match under one light source but do not match under another light source. Commonly experienced with items of clothing, something can appear black under incandescent light but blue under fluorescent light. The scientific reason for this is the differences in the wavelength distribution between the incandescent and fluorescent lights interact with the differences in the spectral reflectance curves of the socks to make them appear the same under one light and different in another.
  • Geometric metamerism –  identical colors appear different when viewed at different angles. A common example is the color variation that appears in metallic paper.
  • Observer metamerism – every individual perceives colour slightly different – “one persons ratio of long wave sensitive cones to short wave sensitive cones may differ from the next person. Therefore, two spectrally dissimilar surfaces may match in the eyes of one individual when viewed under a particular light source but then fail to match when viewed by a second individual under the same light source.”

What do our eyes see?

Our eyes see colour by using three primary colour receptors: red, green, and blue.  At the back of the eye is a small section called the fovea. It has a very high concentration of cones (photoreceptors), allowing us to appreciate colour. The two photoreceptor cells are rods and cones, At very low light levels, visual experience is based  on the rod signal whilst cones require  brighter light. There are three types of cone; short, medium and long which react to blue, green and red. This is the difference between how an light affects an object, and the color it appears to our eyes. Objects selectively reflect or absorb light of different wavelengths, so an object that absorbs most blue wavelengths and reflects most red wavelengths will usually appear red to our eyes.

So there we have it, you may have learnt a new word today! One last fact to leave you with – as we get older our colour perception will deteriorate. This is especially true for men, sad but true!

ref: http://www.beercolor.com/metamerism.htm