UV–vis spectra of the reduction of a typical RBBR ink film from blue
(max = 595 nm) to yellow (max = 472nm)
as a function of UVA irradiation time,t. Spectra were recorded every 10s
of UVA light irradiation. Also shown is the colour change as a series
of digital images. I = 1.5 mW cm−2 368 nm.
(For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)