On the light fading of colorants in hard copy media

Abstract

A simple model for the light fading kinetics of a layer consisting of a molecular dispersion of colorant in a transparent binder is described. The assumptions on which the model is based include:

1.	The distribution of the colorant is uniform.
2.	The colorant is non-scattering.
3.	Incident radiation is uniform over the surface layer.
4.	Internal reflections are absent at surfaces of the layer.
5.	The number of photons absorbed is proportional to the number incident.
6.	There is no inner filter effect.

The theoretical results are compared with those obtained experimentally for various commonly used colorants and substrates. The results predicted by the model generally show good agreement with experimental results, but in some cases departures are found. The model has been modified in these specific cases by taking into account non-uniformities in the layer of colorant. The model provides a simple method for evaluating effective quantum yields as bench mark measures for the light fading of layers of colorants. It enables the prediction of light fading characteristics from measurements carried out over a short time span. The limitations of the model are also considered.

Keywords:

• colorants
• hard copy
• light fading