Light Sources in Color Matching of Plastics
As the Christmas season arrives, I am reminded of an interesting story while working with a well-known company. We had just formed a strategic alliance with a prominent Swedish giant, which was looking out for new suppliers capable of fulfilling their strategy of raw material localization. As I embarked on a visit to their bustling head office, little did I know that my schedule over the next few months would be occupied by a fascinating challenge involving different hues of red that would become the talk of the October-December trimester. The Swedish company, renowned for its quality standards, had a keen eye for detail, even down to the color of their raw materials. It seemed like red had taken centerstage in all their plastic chemistries, demanding meticulous precision and consistency. However, the Nordic winter threw a chilly curveball our way. Cloudy days cast shadows over our attempts to manufacture the perfect red, especially for grades requiring color matching under the unforgiving scrutiny of natural sunlight. Winter's overcast days posed a challenge: the absence of abundant sunlight making color matching a formidable task. This brought forth a revelation - the critical role of suitable lighting in the accurate assessment of colors. I soon learned that the appearance of an object is not just a reflection of its intrinsic color but is profoundly influenced by the light source and the surrounding environment in which it is viewed.
Hence, suitable lighting is crucial for accurately assessing and evaluating the color of objects, as the appearance of an object is significantly influenced by the light source and the surrounding environment in which it is viewed. Consistency in color evaluation is particularly important across different stages of the supply chain, involving various stakeholders. To achieve this consistency, international standards for color viewing have been developed, with two primary standards being widely adopted: ISO 3664:2009 and ASTM D1729-2016.
1) ISO 3664:2009:
- Daylight Viewing Condition: ISO 3664:2009 specifies a D50 daylight viewing condition, which is commonly used in the graphic arts and photographic industries.
- Application: This standard is particularly relevant for industries where accurate color reproduction is critical, such as in graphic design, printing, and photography.
2) ASTM D1729-2016:
- Daylight Viewing Conditions: ASTM D1729-2016 specifies D65 as the primary daylight viewing condition, with additional secondary sources for checking metamerism.
- Applications: This standard has been adopted by various industrial applications, including plastics, paints, textiles, and automotive industries.
Comparative viewing conditions for the standards
Some other standards include SAE J361, which is used in select applications, SAE J361 is a standard that is relevant in specific contexts within the automotive industry. BS-950 Part 2 is another standard used in select applications, BS-950 Part 2, may find relevance in specific industries.
Inspecting under the artificial lamps
(Pic Credits: https://support.hunterlab.com/hc/en-us/articles/202023795-What-is-the-correct-light-level-in-lux-for-a-light-booth-)
Metamerism is a phenomenon where two colors match under one lighting condition but not under another. This inconsistency can be problematic for manufacturers, as colors that appear to match under one light source may appear different under a different light source. This emphasizes the importance of evaluating colors not only under the specified daylight source but also under spectrally dissimilar light sources. This consideration helps ensure that colors remain consistent across different lighting conditions and environments. The lower the color temperature of the light source, the warmer or redder the source will be. Inversely, the higher the color temperature of the source, the cooler or bluer it will be. Common color temperatures, names associated with them, and their associated colors are:
Color Names, Temperatures and colors
(Pic Credits: https://www.gtilite.com/pdf/Various-Light-Sources.pdf)
Adherence to industry standards necessitates meticulous attention to various parameters such as color quality, light intensity, illumination uniformity, viewing/illumination geometry, and ambient conditions. Discrepancies in any of these factors can significantly impact the perceived color. The optimal approach to meeting these stringent requirements involves the utilization of a color viewing booth that aligns with industry specifications.
If you have any other questions or would like to suggest topics for us to write about, please feel free to contact us at prashant.gupta@polymerupdateacademy.com
Author
Dr. Prashant Gupta
Faculty, Polymerupdate Academy
