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It is well known that all materials can undergo more or less significant alterations when subjected to the action of light radiation. The sun's rays that penetrate into a home through the windows, but also other radiation from artificial sources normally found indoors (neon lamps, LEDs, etc.) are forms of energy that, when hitting a surface, can cause even significant changes to its chemical/physical composition.
In furniture, this aspect must always be taken into consideration. Certain polymers (plastics, paints) but above all wood are in fact strongly influenced by light, which can produce even very pronounced surface variations, causing changes especially in colour (yellowing, darkening, etc.), often judged unacceptable by the end user.
 
In order to acceleratethis phenomenon, which normally develops over the course of a few months, and thus to know in advance how furniture surfaces will behave over time, the laboratories use equipment endowed with suitably filtered and calibrated xenon lamps that faithfully reproduce the spectrum of sunlight penetrating the interior. 
The reference test method, which has been carried out at Catas for over 50 years, has been continuously revised to improve it and make it more reliable. The latest edition (2024) of the European standard EN 15187, for which Catas is accredited, contains several significant changes to improve the method, by making it more correlated with natural exposure behind glass.
The most important innovation of the latest revision is undoubtedly the increase in irradiance, that is, the light energy that hits the sample during the test. This increment is obtained simply by extending the duration of exposure, which as announced in a previous news, has now increased to 100 hours compared to the 20 hours of the previous versions.

                                  

Wavelength	Irradiation intensity	Total irradiation	Duration
420 nm	1,1 W/(m2 x nm)	396 KJ/m2	100 hours
(300-400) nm	50 W/m2	18.000 KJ/m2	100 hours
(300-800) nm	550 W/m2	198.000 KJ/m2	100 hours

_{Tab. 1 Correlation between the amount of irradiation and the test time}

 
Furthermore, the concept of measuring the total irradiation (see table 1) that hits the surface of the sample,has been introduced in order to establish the duration of the test.
The instrumental measurement carried out through the use of a radiometer, which is located on board the devices and which is now present also in the most economical versions of them, will significantly improve the internal repeatability and reproducibility of the test when carried out by different laboratories.
The previous editions of the standard in fact required that the duration of the test, and therefore of the irradiation, were established based on a visual evaluation carried out on photosensitive materials (the blue wool standard) exposed at the same time as the samples being tested. Obviously, although relatively precise, this method was always linked to the subjectivity of the operator who had to possess the necessary experience obtainable only with years of tests and continuous comparisons with other laboratories.
This significant result, the use of radiometers, was obtained thanks to a very complex and detailed study carried out on different devices equipped with different irradiation control systems.
The complexity arose above all from the evidence that the different instruments carry out irradiation measurements in different wavelength ranges.
However, the tenacity in the research coordinated by Catas, which involved seventeen laboratories from all over the world for several years, finally led to the desired positive results.
 
Now the next target on the standardization table is to publish an international standard (ISO) by 2025, starting from the current version of the European standard EN 15187. Thanks to the long experience on these issues, Catas has already been designated as an authoritative Institute to coordinate this further important work.



For info:
Claudio Caon
+ 39 0432 747224
[email protected]