Color Science

Ever since I have been able to comprehend things, I have loved color! We all have our favorite colors, mine is blue. But what exact blue am I talking about? How could I relay exactly what type of blue I mean to you and what exactly is color?


Where Does It Come From?

Well, color is caused by differing qualities of light being reflected (or emitted) by an object. There cannot be color in the absence of light because when light shines on an object the color we see is the light wave that gets reflected while the others are absorbed. The wavelengths vary in size with red being the longest and blue the shortest. If all the visible wavelengths are combined then we see a white light and you may think white light has no color but if this light shines through the water we see a rainbow. Inside our eyes are cones that help us see waves as colors and the waves reflected off objects get translated by our eyes and brain into the color of the object. But how can we quantify this and how can we distinguish between the colors that ever our eyes can barely perceive?


How Can We Measure Color?

A long long time ago, in the 1940โ€™s, a man named Richard Hunter came up with a three number system that was scaled to show how the eye perceives colors and color differences. Later called CIELAB (CIE unintuitively stands  for International Commission on Illumination) or L*a*b*, this method works essentially as an xyz coordinate system with the L representing lightness from black (0) to white (100), the a from green (-) to red (+), and the b from blue (-) to yellow (+). This method was tweaked to perfection and now CIELAB has been designed so that the same amount of numerical change in these values corresponds to roughly the same amount of visually perceived change. Pretty cool right? A special instrument called a spectrophotometer is used to read these values.


Spectrophotometer

The way a spectrophotometer works essentially is light is blasted at a certain angle onto the surface to be measured, the reflected light is measured in the device and the LAB readings are displayed on the screen for you to read. You can compare any two colors and receive a delta E value which can be calculated in a way resembling the Pythagorean Theorem. You can do this manually or the spectrophotometer can do it for you, see the equation below.

ฮ”E =(๐ฟ2โˆ’๐ฟ1)2+ (๐‘Ž2โˆ’๐‘Ž1)2+(๐‘2โˆ’๐‘1)2

This ฮ”E value will tell you how different the two colors youโ€™re comparing are. Usually, between a ฮ”E value of 0 – 1, the observer cannot tell any difference. Between 1 – 2, you can see minimal color differences. Between 2 – 4, there is a perceivable color difference and between 4 – 5 there is significant color difference. Anything above a ฮ”E of 5 is a different color. It has been found that the Just Noticeable Difference (JND) for most people is around ฮ”E = 2.3.

Many industries rely on accurate color matches for customer satisfaction which makes spectrophotometers and LAB incredibly useful tools. You may have to pick up a spectrophotometer and see how your eyes compare to the average JND or start discovering what your favorite colorโ€™s LAB number is.

Author

Madeleine Smith
Chemistry Intern

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