Fluorescence

/ˌflʊərˈɛsns/

General Definition

Fluorescence in the printing industry refers to the ability of certain materials, especially papers, to absorb invisible ultraviolet (UV) light and re-emit it as visible blue light. This property is typically introduced by additives called Optical Brightening Agents (OBAs) to make the paper appear whiter and brighter than its natural color. While fluorescence may be visually appealing, it poses a severe challenge in accurate color measurement because the amount of light reflected from the sample heavily depends on the UV content of the light source used.

Real-World Usage

The use of papers containing OBAs is very common in commercial printing and packaging, but it presents a major headache for color managers. The reason is that colors printed on a fluorescent paper appear different depending on the ambient light (store lamps or sunlight). To standardize measurement, organizations like ISO have established standards for measuring instruments. For example, M1 measurements (according to ISO 13655) include a specific level of UV that simulates the standard D50 Illuminant conditions to incorporate the effect of fluorescence in the measurements.

Ignoring the effect of Fluorescence can lead to significant errors in quality control. Assume a sample has an acceptable ΔE value under the controlled D50 light in the pressroom, but the same sample appears distinctly bluer and brighter under ambient light with higher UV content, such as in a store environment. This unintended color shift, especially in white and pastel colors, can lead to customer dissatisfaction and brand color mismatch. Therefore, selecting measuring instruments capable of controlling the UV content (such as M0, M1, M2 modes) is essential for color management in packaging.

Consultant's Note

As a production consultant, it is suggested that, when defining color standards, the issue of lighting responsibility segmentation must be specified in contracts. If the topic is quality control during production, color management in the pressroom, or matching a technical standard proof, you must insist on the D50 standard. However, if the color evaluation is at the stage of retail display, final approval by the brand owner, and consumer inspection, the D65 standard must be the benchmark. The difference in the UV content of these two light sources affects how fluorescence is perceived.

The key point here is the M1 Measurement Condition. Fortunately, M1 is designed according to ISO 13655 to serve as a stable measurement mode that accurately calculates and records the effects of fluorescence (caused by OBAs) under both D50 and D65 lighting standards. In other words, M1 is the method used for measurement when the effect of OBAs needs to be considered (whether in D50 or D65). Therefore, synchronizing the process with M1 ensures that your spectral data sees exactly what the buyer sees under the light relevant to that environment (D50 for production or D65 for retail). This path is the only scientific solution to overcome the challenge of Fluorescence.

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