https://doi.org/10.1351/goldbook.08608
Angle of incidence of a beam of electromagnetic radiation greater than \(\pu{70\!^{\circ}}\).
Note:
Ideally the angle of incidence should be greater than \(\pu{80\!^{\circ}}\).
Ideally the angle of incidence should be greater than \(\pu{80\!^{\circ}}\).