Lightfastness is the color fastness of colourants , varnishes and other surfaces with prolonged lighting. Sunlight in particular, with its high proportion of UV light, has a corrosive effect on many materials, which can lead to visible color changes.
We also speak of lightfastness for clear surfaces and materials such as glass and plastics . The color change or darkening has not only aesthetic but also technical disadvantages, such as in algae cultivation systems. Glass is less sensitive to solar radiation than plastics.
In the artists' paint industry, lightfastness is divided into four classes:
- *** highest light resistance
- ** very good lightfastness
- * Sufficient light resistance
- low light resistance
The blue scale according to the no longer valid DIN 53952, on the other hand, was somewhat more detailed:
- Light fastness 8: excellent
- Light fastness 7: excellent
- Light fastness 6: very good
- Light fastness 5: good
- Light fastness 4: pretty good
- Light fastness 3: moderate
- Light fastness 2: poor
- Light fastness 1: very poor
The adjectives are firmly agreed for this.
Inorganic pigments can be significantly more lightfast; Wehlte suggests an extension up to 10 (9: perfect, 10: absolute). Most pigments have a lightfastness of 7 or higher. With its original meaning for textile dyes , however, lightfastness 8 is rare.
The measurement method consists of a comparison with a scale of eight blue wool strips of different lightfastness, which are exposed to light with the sample. The exposed sample is compared with a covered sample part. The level at which a "clear" (up to level 6) or "just recognizable" (levels 7 and 8) difference can be seen is then specified as lightfastness. With each stage, the time in which the sample can be exposed to light is roughly doubled without it changing. With lightfastness 7, this corresponds to about a year outdoors in Central Europe.
- PDF ink (jet) printing, including measurement method of lightfastness ( memento from January 25, 2011 in the Internet Archive ) (501 kB)
- Notes on the duration of possible solar radiation depending on the lightfastness ( memento from February 10, 2013 in the web archive archive.today )
- N. Schultz, F. Wintersteller: Status and Trends of Photoautotrophic Algae Cultivation from the Viewpoint of a Glass Manufacturer. (PDF) (No longer available online.) SS12 , archived from the original on July 14, 2016 ; accessed on July 14, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.