The literary device uses in the one ‘ Rainbow tinted circles of light' is an imagery.

In the poem ‘Bangle sellers' by Sarojini Naidu, the poetess simply try to explain the beauty of the shiny, colourful bangles.

They are circular in shape, they reflect light and thus, they are shiny.

This line is just a  way of saying, shiny, circular bracelets of multiple colours.