Abstract: An article of apparel (1, 601) has a chamber (9, 605) and a light source (11, 607) for illuminating the chamber with Light. The chamber (9) contains particles (900) which can scatter or reflect light from the light sources and has a window (9a) through which the effect of the particles (900) on the light from the light sources (11) can be viewed. Alternatively, the chamber (605) contains a light affecting means (606, 901, 1001) for reflecting, refracting or diffracting light from the light source (607). The light affecting means (606, 901, 1001) is moved by a hydraulic system (800) or vibrates in response to motion of the article of apparel (601).