= dead brightness

olemus
ultraviolettkiirgusetundetu, näiteks nõudena põhimikule (paber, plast), millele kantakse UV-tundlikke turvaelemente
= not exhibiting brightness or fluoresce when exposed to ultra-violet light

ülevaateid
domtar.com:
UV Dull or Dead Brightness
— Most printing papers are manufactured with optical brightening agents (OBAs), which help reflect invisible light into the visible spectrum and create a nicer-looking printed document. But these OBAs fluoresce under black light. Security papers made with UV dull or dead levels give bank employees a way to check for forgery by simply passing the check under a black light. Any sign of fluorescence is a clue the check might be a copy.

https://tradepractices.wordpress.com/
“Security paper has to be “UV-dull” – unlike most commercial papers, which are artificially brightened.
Brightening agents absorb ultraviolet radiation and reradiate visible light in the blue region of the spectrum, making commercial paper look brighter and more neutral in color. UV-dull paper improves security by allowing the use of fluorescent inks as a security feature, the appearance of which would be altered by brightened paper, and by not fluorescing under UV light as would counterfeits produced on ordinary, brightened commercial paper.”