We do not carry out a test to determine light resistance to infrared light and are therefore unable to provide any information in this respect. In principle, however, it can be said that the light resistance of edding inks is measured according to the wool scale. However, we have not classified every pen. In principle, pigmented inks, such as those used by the edding 750, have a higher light-fastness than inks containing dyes. How long an ink remains lightfast depends very much on a number of factors, such as weather conditions, sunlight, humidity, etc.