Optical brightening agents (OBAs) are chemicals that manufacturers add to products like paper, plastics, and textiles to make them appear whiter and brighter, and to lessen the natural yellowing process that happens over time. They also add these chemicals to cleaning agents to enhance the appearance of materials – primarily textiles – after cleaning.
OBAs trick our eyes into seeing a brighter white. Objects themselves don’t have color... they have dyes, colorants, or pigments that absorb some wavelengths of light and reflect others. The color you perceive is the color of the light that is reflected off of the object – what we perceive as the visible spectrum.
The visible spectrum, shown below, is only the light that we can see with the naked eye. Since it’s the only part of the spectrum we can visualize, many of us consider it all-encompassing, but it’s really just a tiny part of the electromagnetic spectrum.
This graph shows the reflectance curves of black, blue, green, gray, red, and white.
Watch what happens to the white curve when we add optical brightening agents...
See how the peak rises in the blue area?
OBAs absorb light from the ultraviolet region of the electromagnetic spectrum that we can’t see and re-emit that light in the blue region where we can see it. Our eyes will perceive this white to be brighter than the white that doesn’t contain optical brighteners.
Although OBAs help manufacturers sell more products, they make it very difficult to control color because the optical brightening content can only be seen under light sources that contain UV. Before assembling products with pieces from different suppliers, manufacturers need to evaluate the amount of optical brighteners in each to ensure consistency after final assembly and under all of the lighting conditions the product will be exposed to out in the world.