Illuminant dependency from the spectral world and fluorescent whitening agents

First of all, please compare these images:

There should be quite a few facts. I want to focus on these facts:

• According to the scanner, the photo paper is darker than the ceramic tile. But under Xenon flash, it is the opposite.
• Under Xenon flash, the colors shift to cyan. The photo paper’s image shifts to green-ish cyan, and the ceramic tile’s image shifts to blue-ish cyan.
• The ceramic tile’s image shows smaller color shift than the photo paper’s image. (Look at the gray patches of them, especially.)

Fluorescent whitening agents

The illuminant of EPSON Perfection V600 is CCFL. It contains almost no UV light. Xenon flash contains rich UV light. Fluorescent whitening agents require UV light to do their job. They sleep under CCFL, and work under Xenon flash. Now you’ll see the photo paper contains fluorescent whitening agents, and the ceramic tile doesn’t.

Illuminant spectrum

Xenon flash contains rich near-UV light too. Most yellow inks absorp 400-450 nm light well, but not much near-UV light. So near-UV rich light often makes printed image colors cyan-ish.

Ink quality matters

The photo paper’s ink set is cheap compatible. The ceramic tile’s ink is SubliNova. Under mild condition, there is no difference. But under hard condition like Xenon flash or sunlight, ink quality matters.