Textiles and Optical Brightening Agents

Beginning around the 1930’s, the rules of fashion dictated no white before Memorial Day. It was a status symbol, when the wealthy left their winter garments behind and headed to the beach for the summer with their lightweight, carefree clothes.

Although the rule still loosely applies, modern day fashion is more concerned with the brightness of your whites than when you start wearing them. So how do manufacturers ensure their products are as white as they can be?

Optical brightening agents (OBAs) are chemicals that are added to everything from linen slacks and silk blouses to socks and underwear. They use the process of fluorescence to trick your eyes into believing your clothes are whiter and brighter than they actually are. To ensure your garments enhance and retain this whiter than white appearance, many laundry detergents contain optical brighteners, too.

To understand how they work, we need to step back into elementary school science class.

This is the visible spectrum – the light that we can see with the naked eye – and only a tiny part of the electromagnetic spectrum.

This is the electromagnetic spectrum. It starts on the far left with gamma rays and travels to the right through x-rays, microwaves, and radio waves. See the tiny visible spectrum that falls between ultraviolet and infrared? That’s the only part humans can see with the naked eye… unless OBAs are involved.

OBAs absorb a portion of the invisible ultraviolet rays and reemit them as blue light. It’s this reflected blue light that makes fabrics look brighter and whiter.

It’s easy to detect the presence of optical brighteners under a black ultraviolet light. Fabrics and detergents that contain more OBAs will appear brighter than those with less.

This laundry detergent contains optical brightening agents. Notice how it appears to glow under UV light?

While clothes containing OBAs may appear the same in the store, they can look different under light sources that contain more UV light. Herein lies the challenge for manufacturers who assemble outfits using pieces of fabric from different suppliers. Although the sleeve and collar may match under store light, those colors can shift under UV light sources.

Although these white shirts look great under daylight, when placed in a light booth under UV light, you can see that the white pieces all contain different amounts of optical brighteners.

Manufacturers who use OBAs in their fabrics must use consistent amounts, or the difference will be noticeable to consumers. When assembling clothing with parts from different suppliers or fabric from different lots, manufacturers must evaluate the amount of optical brighteners to make sure the products will retain their appearance once they’re exposed to UV light.

Understanding OBAs and how they affect substrates gives you some insight into why manufacturers need to control color so carefully. The most effective ways are to use a light booth (like the one above) to visually evaluate the amount of optical brighteners, or a spectrophotometer with calibrated UV illumination, like the X-Rite Ci7800 or Ci64UV, to measure and quantify this effect.

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