Part I – OBAs and Color Reproduction
For printers, color is everything. Even paper has color. Paper color can drastically affect printed color. In the pursuit of predictable color, white isn’t just white anymore.
We’ve all seen ads for toothpaste and laundry detergent promising whiter whites. Optical brightening agents (OBAs) have been added to these products to create the whitening effect. OBAs stay on the surface of fabrics and teeth and literally change the color you see from yellowish to blue-white. Our eyes see blue-white as cleaner and brighter than yellow-white.
OBAs have been added to paper for the very same reason: Print customers want whiter whites.
The whites look whiter because OBAs absorb invisible UV light (when available) and re-emit it as visible blue light. Call it science, voodoo, or just plain cool (pun intended), the result is a bluer white that looks brighter in daylight or any light source that has some UV light in the mix.
NOTE: This effect only happens when the light shining on the OBAs includes UV light. If there is no UV light available, there is no whiter, brighter effect. OBAs change UV energy into visible, blue light, so no UV means no white-blue voodoo.
Brighter white is great news for color, with one exception. When OBAs first came into use on paper, standard viewing booths and color measurement instruments (spectrophotometers) were not prepared to handle them. This meant measuring and re-creating color on OBA enhanced substrates was next to impossible.
This was a two part problem:
- The lamps in standard viewing booths for the printing industry radiated very little UV light. The OBAs didn’t activate, so the whiter, brighter effect couldn’t be evaluated during the visual approval process.
- Spectrophotometers used to measure paper and color ‘saw’ paper white differently than the human eye in industry standard viewing booths. This lead to color evaluation challenges when comparing printed samples to proofs calibrated using these instruments.
Because OBAs introduced a disconnect in the visual approval process, new lighting standards were developed for viewing booths and spectrophotometers. Follow our next few blogs as we discuss the impact these new standards have on the printing process. Do they solve the OBA issues?