Painted in 1981, Bright Day belongs to a group of works that were inspired by a trip to Egypt that Riley made in the winter of 1979-80. Paul Moorhouse comments, 'During that trip she visited the Nile Valley and the museum at Cairo, and was able to study, at first hand, the tombs of the later Pharoahs in the Valley of the Kings. Riley was astonished by the art she found in these ancient burial sites carved out of rock and located deep in the earth. These sacred places were dedicated to the dead, yet the tomb decoration was a vivid evocation of life and light. Though their creators had used only a limited number of colours - red, blue, yellow, turquoise, green, black and white - the walls of the chambers receded behind images in which could be seen a bustling affirmation of everyday existence. In looking at the art and craft of Ancient Egypt in the Cairo Museum, Riley recognised that the same colours had been used in all aspects of the Egyptians' material lives, from the decorative to the purely functional.
'On her return to London, Riley found that these colours continued to exercise a fascination. Any possibility of using them in her work was, however, tempered by concern about an implicit act of appropriation. These misgivings were assuaged during the process of recreating the colours when she felt it was important to work from memory, rather than copying the palette from reproductions in books. As she began to explore this new, so-called 'Egyptian palette', it was clear that radical structural changes to her work would be required. Though limited in number, the admission of a range of intense colours needed a formal vehicle that was simpler than the curve she had been using for the last six years. For this reason she now returned to the more neutral stripe ... The stripe paintings made between 1980 and 1985 reveal a progressive structural reorganisation and in that sense they are an important watershed in Riley's work. They form a passage from the perceptual - optically mediated - character of her art before 1980, to her work from the early 1980s onwards which addresses pure sensation directly: visual experience as a direct response to its source. Riley made this distinction clear as follows:
'Right up to, and in some ways including, the stripe paintings I used to build up to sensation, accumulating tension until it released a perceptual experience that flooded the whole as it were. Now I try to take sensation as the guiding line and build, with the relationships it demands, a plastic fabric which has no other raison d'être except to accomodate the sensations it solicits'' (Exhibition catalogue, Bridget Riley, London, Tate Britain, June - September 2003, p. 22).