Umucu noma ishidi eliguqukayo elinamakha azwela ukukhanya, elibhala isithombe kuqala njengoshintsho olungabonakali, futhi libonakale kuphela emva kokuhlanzwa ngamakhemikhali. Lithengiswa ngosayizi abahlukene, ngokumnyama nokumhlophe noma ngemibala, nangamandla ahlukene okuzwela ukukhanya — ifilimu ezwela kakhulu idinga ukukhanya okuncane kodwa izinhlayiya zayo zibonakala kakhulu.