Display apparatus

A display apparatus, comprising:

• a reflective layer comprising reflective material, and one or more stacks of additional layers provided on a first side of the reflective layer, wherein each stack comprises an optically switchable layer;
• a plurality of switching elements located on a second side of the reflective layer opposite to the first side or forming part of the reflective layer, each switching element being operable to apply a signal through the reflective layer to a switchable portion of the optically switchable layer and thereby change an appearance of the switchable portion when viewed from a viewing side of the display apparatus, wherein
• the optically switchable layer comprises a phase change material, the phase change material being switchable between a plurality of stable states, each of the stable states having a different refractive index relative to each of the other stable states, the phase change material being switchable by application of heat between the plurality of stable states;
• and
• the optically switchable layer is configured such that switching of the optically switchable layer causes the apparatus to provide one or both of the following effects for incident radiation within a predetermined frequency range:
• (i) a change in reflectivity of a factor of at least 50;
• or
• (ii) a change in phase that is within 5% of nπ/2 radians, where n is an integer.