Measures for limiting disturbing reflections on screens significantly depend on the level of screen luminance and the type of antireflection coating of the screen. With increasing screen luminance, reflections on the screen surface cease to be disturbing. This applies particularly for screens with positive polarity where black characters are displayed on a bright background. Hence, higher-luminance disturbing light sources are permissible for high screen luminance and positive character display. The optical characteristics of screens are set out in EN ISO 9241-307 "Ergonomics of human-system interaction – Part 307: Analysis and compliance test methods for electronic visual displays" (2008). It is the basis for the luminance thresholds for luminaires capable of reflecting off the screen standardised in EN 12464-1 (see table). This standard contains requirements for examination, certification and conformity procedures for screens of various technologies, namely cathode ray tubes (CRT), liquid crystal displays (LCD), plasma display panels (PDP) and portable screens (laptops). It refers to measurement methods according to ISO 9241-305 and general requirements for visual displays according to ISO 9241-303.