What is ISO 18937 about ?  
 ISO 18937 describes test equipment and procedures for measuring the light stability of colour photographic reflection prints designed for display, when subjected to a filtered xenon-arc light source simulating daylight through windows at specified temperatures and relative humidity.
ISO 18937 is applicable to photographic reflection prints, made with analogue and digital print processes. The recommended test methods can be applied to both colour and black-and-white photographic prints. This test method assesses colour and density change.
The length of time that such photographs are to be kept can vary from a few days to many hundreds of years and the importance of image stability can be correspondingly small or great. Often the ultimate use of a particular photograph may not be known at the outset. Knowledge of the lightfastness level of colour photographs is important to manufacturers to improve print materials and too many users, especially since stability requirements may vary depending upon the application.
Who is ISO 18937 for ? 
 ISO 18937 on methods for measuring indoor light stability is useful for
- Photographers
- People working in the photography industry
- Quality assessors of photograph
Why should you use ISO 18937 ?  
ISO 18937 addresses the methods and procedures for measuring the indoor light stability of photographic reflection prints.
The light stability of colour photographs is influenced primarily by the intensity of the radiation/light source, the duration of exposure to light, the relative spectral irradiance of the light source, and the ambient temperature and humidity conditions. Ultraviolet radiation is particularly harmful to some types of colour photographs and can cause rapid fading as well as degradation of the underlying substrate. Information about the light stability of colour photographs can be obtained from accelerated light stability tests specified in ISO 18937. Accelerated light stability tests in ISO 18937 for predicting the behaviour of photographic colour images under normal display conditions may be complicated by “reciprocity failure."
What’s changed since the last update ? 
BS ISO 18937:2020 supersedes BS ISO 18937:2014, which is withdrawn.
BS ISO 18937:2020 replaces BS ISO 18937:2014, which has been technically revised. The main changes are as follows:
- Removal of non-xenon light sources
- Removal of non-essential verbiage to improve method clarity
- Inclusion of annex on actual sample temperature measurements during exposure
- Inclusion of continuous phase test for in-window display conditions
