The hologram stayed completely readable. The hologram’s light background turned yellow during the test – only slightly, but nevertheless so that it could be detected visually. The UV energy accumulated during the testing would, in constant outdoor use in natural outdoor conditions, accumulate in one and half a year, on average, in Southern Finland.
The testing examined changes caused by UV radiation to the security holograph and its readability.
The samples were subjected to a stress by UV radiation that resembles the sun’s UV radiation. In addition, the test was accelerated by increasing the radiant power to approximately double it in comparison with that of the sun on a sunny summer day. The sample temperature during the testing was 32°C. The samples were subjected to measurements of colour and index of yellowness every 5 days. In addition, they were visually examined and photographed. The total duration time of the test was about one month (764 hours).