In white-beam topography, all misoriented crystallites will be diffracting simultaneously (each at a different wavelength). The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Iridescent colors are strongest when the diffracting droplets are small and similar in size. A similar analysis with particles diffracting through multiple slits is given by Richard Feynman. Lithium fluoride is used also as a diffracting crystal in X-ray spectrometry. Furthermore, PCs function by diffracting light.