Comparatively Speaking: Color vs. Fluorescence

By: Anthony J. O'Lenick Jr., Siltech LLC

Posted: March 20, 2012

Color is perceived by the brain when light that has been separated into its individual component wavelengths has been reflected to human eyes by an object or substance. Fluorescence is a different phenomenon, as the emission of light by an object or substance that has absorbed light (usually UV wavelengths) and then emitted light with a longer wavelength.

Materials that fluoresce are referred to as optical brighteners and are used in consumer products. According to Wikipedia, optical brighteners are dyes absorb light in the ultraviolet and violet region (usually 340–370 nm) of the electromagnetic spectrum and re-emit light in the blue region (typically 420–470 nm). These additives often enhance fabrics or paper by producing a whitening effect to make these materials look less yellow though an increase of the amount of blue light reflected.

Similarly, “bluing” used to be added to a load of laundry the make clothes whiter. Unfortunately, optical brighteners are not approved color additives for cosmetics in the United States. However, ingredients that provide visual effects that can alter the performance and visual properties of a product are certainly not prohibited.

The importance of color to the cosmetic chemist is clear, but the importance of fluorescence in cosmetic formulations is somewhat more obscure. Visual perception of cosmetics is equally important, and the search for ingredients to improve the visual appearance of the skin is ongoing. Ingredients, even if they are color additives, can be used for this purpose as long as they are approved for such use.

A patent issued in 1998 notes, “The control of specular versus diffuse reflectance in cosmetic formulations is a function of the appearance enhancing characteristics desired for the cosmetic composition. The addition of small quantities of fluorescent compounds added to cosmetic formulations increases the apparent luster, shine or color intensity of the composition. Further, the use of these materials extends to translucent or opaque color cosmetic formulations such as lipsticks, nail enamels and the like where the incorporation of fluorescent brightening compounds into the composition increases the apparent color intensity.”