Assertion: lens's index | /r/HasProperty | written as n d
Facets:
value: often
type: TEMPORAL
Source sentences:
text: The choice of glass gives the mean refractive index, often written as n d {\displaystyle n_{d}} (for the refractive index at the Fraunhofer "d" spectral line wavelength), and the Abbe number V {\displaystyle V} (for the reciprocal of the glass dispersion).