Whiter Than White - Fluorescence Effect

All color including white can be defined with a minimum of three numbers (learn more about the science of color - from Perception to Instrumentation, click here). What distinguishes white from other color is it’s high lightness and low saturation. It is more attractive with a bluish than with a yellowish cast.

Whiteness is caused by a combination of high lightness and lack of yellowness. Yellowness is usually undesirable in whites as it is associated with product deterioration. Whiteness with blueness is perceived as clean and therefore seems brighter.

High brightness is achieved with the aid of fluorescent whitening agents (FWA) or optical brightener agent (OBA). These are additives designed to enhance the appearance of brightness in fabrics, detergent and papers.
It may also enhance or modify the appearance of the white. FWAs increase the whiteness of a substrate by absorbing ultra violet light and re-emitting blue fluorescence. This overcomes the natural slight yellowness of the substrate to give an intense whiteness. FWAs are commonly used in washing detergents, paper and fabric. White paper and fabrics with FWA appear whiter than normal under UV illumination. Most commercial white fabrics are treated with FWAs. Similarly, washing detergents are formulated with FWAs to maintain the whiteness.

The paper samples below are illuminated by tungsten, TL84, D65 and UV lightings. Tungsten lighting has little or no UV energy and the FWA is not excited to make it flourescence. TL84 and D65 has some UV energy and the samples looked 'whiter'. Under UV lightings, the FWA are excited and produce a whiter than white look.

The spectrum graph shows an incremental amount of UV energy gives higher reflectance.