How light affects colour
The appearance of a surface colour is defined by the product of the spectral reflectance curve of the material and the spectral emittance curve of the light source shining on it.
As a result, different materials and surface finishes in combination with different light sources, whether artifical or natural, can make colours appear different. In the same way, the colour of two samples can appear the same under one light but different under another – known as a metameric failure or more accurately, an illuminant metameric failure.
Most types of fluorescent lights produce an irregular or peaky spectral emittance curve, so that two materials under fluorescent light might not match, even though they are a metameric match to an incandescent white light source with a nearly flat or smooth emittance curve.
Other metameric failures such as a geometric metameric failure can occur when two samples match when viewed from one angle, but then fail to match when viewed from a different angle. This kind of failure is especially common in metallic or pearlescent finishes.
Finally, a field-size metameric failure can occur because the relative proportions of the three cone types in the retina vary from the centre of the visual field to the periphery, so that colours which match when viewed as very small, centrally fixated areas may appear different when presented as large colour areas.
Colours can also look different, dependant upon the background or surrounding colours and in contrast, different colours can also look the same. See the identical colour swatches below:
You will notice from the same colour stack on the right that when a divider obscures the joint between two colours, then the difference is eliminated and the colours appear the same.
When colour matching to a sample, it is important for the customer to understand the possibility of metameric failure. To achieve the best possible results, Asia Poly’s colour lab need to know details of the product in its final application. Armed with this information, any colour match can be compared under the correct conditions.