220.127.116.11.1 Semantic definition
IfcSurfaceStyleRefraction extends the surface style lighting, or the surface style rendering definition for properties for calculation of physically exact illuminance by adding seldom used properties. Currently this includes the refraction index (by which the light ray refracts when passing through a prism) and the dispersion factor (or Abbe constant) which takes into account the wavelength dependency of the refraction.
18.104.22.168.2 Entity inheritance
The index of refraction for all wave lengths of light. The refraction index is the ratio between the speed of light in a vacuum and the speed of light in the medium. E.g. glass has a refraction index of 1.5, whereas water has an index of 1.33
The Abbe constant given as a fixed ratio between the refractive indices of the material at different wavelengths. A low Abbe number means a high dispersive power. In general this translates to a greater angular spread of the emergent spectrum.
22.214.171.124.4 Formal representation
ENTITY IfcSurfaceStyleRefraction SUBTYPE OF (IfcPresentationItem); RefractionIndex : OPTIONAL IfcReal; DispersionFactor : OPTIONAL IfcReal; END_ENTITY;