Fig. 3. Calculated spectral reflectivities for an ideal quarter-wavelength (/4) stack with 10 platelets of chitin and spaces of cytoplasm at angles of incidence from 0 to 80° (_max=660nm at normal incidence) (calculated by D. M. Rowe). The degree of shading at each point in the two diagrams represents reflectivity: the lighter the shading, the higher the reflectivity (ranges given below figure). (A) For light polarised in the plane perpendicular to the plane of incidence. (B) For light polarised in the plane parallel to the plane of incidence. Changing the angle of the incident light from 0 to 25° only shifts the wavelengths best reflected from 660nm to approximately 610nm, while a change in the incident light from 45 to 55° shifts the wavebands best reflected from 500 to 440nm.