The second part of the N.P.L.'s colour-matching investigation was devoted to determining average colour-matching properties in a large (10 ° diameter) bipartite matching field, and the final corrected results are here presented in tabular form, together with a specification of the conditions of measurement, and ancillary data on repeatability. The tabulated results comprise (a) mean colour-matching functions, referred to reference primaries at wave-numbers 15 500, 19 000 and 22 500 cm -x, for spectral stimuli in the range 12 000 to 25 500 cm -~, given at intervals of 250 cm -1 between i6 000 and 22 000 cm -1 and at intervals of 500 cm -1 outside these limits, (b) the standard deviations and correlation coefficients of the colour-matching functions at wave-numbers between 14 000 and 25 500 cm -~, (c) mean colourmatching functions corrected for rod intrusion in the range 12 000 to 17 000 cm -1, (d) the corresponding mean unit coordinates in a W.D.W. system, and their standard deviations, (e) the mean relative luminosity factors of the reference primaries and their standard deviations determined by both directcomparison and flicker heterochromatic matching, (f) the mean relative luminosity function Va in the range 12 000 to 15 000 cm -1 determined by direct comparison with 14 250 crn -1. The main colour-matching results are based on 49 subjects, but the results for spectral stimuli of wave-number less than 14 000 cm -~ rest on fewer subjects. The extent to which the results show an increase with age in the yellow pigmentation of the eye is discussed.

Lead halide perovskites have attracted great attention due to their excellent optoelectronic properties, with great progress being made in their performance as light emitting diodes (LEDs), photodiodes, and solar cells. Demonstrating large scale, high-resolution patterning of perovskites

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Metasurface holograms are usually realized on flat surface topologies. Here we show that flexible holographic metasurfaces can be designed to form an image when applied to arbitrary substrate shapes. We demonstrate that for non-flat surfaces the phase contribution of the substrate determines the symmetry properties of the image. The sensitivity of the hologram to the specific surface topology can be enhanced by engineering the distribution of the phase elements in the metasurface area. The results of this work pave the way for practical applications in security printing technologies, in addition to surface topology and polarization sensors.

Local displacements in the plane of an object surface illuminated by coherent light may be measured by recording double-exposure photographs of it. When the surface is illuminated symmetrically by two oblique beams, 'speckle correlation fringes' appear in the doubly exposed negative, due to the nonlinear nature of the photographic recording. Factors affecting the visibility of these fringes and the range of displacement which can be measured are discussed. The fringe visibility falls to zero for displacements larger than a speckle width, but measurements can then be performed upon the optical transform of the negative image. With uni-directional object illumination, the in-plane displacement can be measured on a point-by-point basis in magnitude and in direction from Young's fringes observed. With two symmetrical oblique illuminating beams the effect of a small surface strain is displayed, even if large lateral displacement has occurred, by using spatial filtering when viewing the photographic image.