Optically Bright Textiles
By Erika Simmons
Ultraviolet (UV) is a form of electromagnetic radiation with a wavelength between 10nm to 400nm. It’s shorter than the visible light spectrum but not as long as X-rays. UV is present in sunlight; it comes in both long and short wavelengths. We are familiar with the shortwave UV because it can cause sunburn. It’s also responsible for formation of Vitamin D which is needed for good health.
The long wavelength UV is not considered an ionizing radiation, but it does cause chemical reactions that makes substances glow or fluoresce.
Optical brighteners are chemical additives that have molecules which fluoresce.
They may be referred to as Optical Brightening Agents or Fluorescent Whitening Agents. Optical brighteners intensify the whiteness of textiles by absorbing the UV part of the daylight spectrum and re-emitting the energy as visible light. This is known as fluorescence.
White and light textiles that have been optically brightened can prove challenging from a measurement perspective because the UV absorption properties of fluorescent whitening agents used for textiles differ from those used in plastics, paper, and other mediums. Whiteness indices (WI) are used to communicate the whiteness.
There are two commonly used indices: the Ganz-Griesser whiteness and the CIE Whiteness Index.
When measuring whiteness in textiles, it is important to have standard references that are comprised of textile materials. AATCC offers a UV Calibration Reference fabric and EP11-2016e Evaluation Procedure for UV Energy and Optically Brightened Textiles: Spectrophometer Calibration provides guidance for using the standard.
AATCC Textile Ultraviolet Calibration Standards (TUVCS) for spectrophometer light sources was developed to increase accuracy and quality of the electronic data communication.
For more information visit www.aatcc.org/testing/uv