A light emitting device comprising: a device which serves as a primary light source of blue light; and a population of photoluminescent quantum dots disposed in a host matrix, wherein the host matrix comprises at least a first layer and wherein the host matrix is a polymeric matrix; wherein at least a portion of the quantum dots have a band gap energy smaller than the energy of at least a portion of the light produced by the source, and wherein the matrix being disposed so as to allow the light from the source to pass therethrough, thereby causing the quantum dots to photoluminesce light of a color characteristic of their sizes, characterized in that the light emitting device is a white light emitting device; the population of photoluminescent quantum dots comprises a first subset of quantum dots selected to emit red secondary light when irradiated by the primary light source and a second subset of quantum dots selected to emit green secondary light when irradiated by the primary light source, wherein: (a) both the first subset and the second subset of quantum dots are dispersed in the first layer of the host matrix, such that the host matrix comprises the first subset of quantum dots selected to emit red secondary light and the second subset of quantum dots selected to emit green secondary light dispersed in the same layer, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source; or (b) the first subset of quantum dots selected to emit red secondary light is dispersed in the first layer of the host matrix, and the host matrix further comprises a second layer comprising the second subset of quantum dots selected to emit green secondary light dispersed therein, wherein the first layer is disposed to allow the green secondary light from the second layer to pass therethrough, wherein the first layer and the second layer are adjacent to one another, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source. a device which serves as a primary light source of blue light; and a population of photoluminescent quantum dots disposed in a host matrix, wherein the host matrix comprises at least a first layer and wherein the host matrix is a polymeric matrix; wherein at least a portion of the quantum dots have a band gap energy smaller than the energy of at least a portion of the light produced by the source, and wherein the matrix being disposed so as to allow the light from the source to pass therethrough, thereby causing the quantum dots to photoluminesce light of a color characteristic of their sizes, characterized in that the light emitting device is a white light emitting device; the population of photoluminescent quantum dots comprises a first subset of quantum dots selected to emit red secondary light when irradiated by the primary light source and a second subset of quantum dots selected to emit green secondary light when irradiated by the primary light source, wherein: (a) both the first subset and the second subset of quantum dots are dispersed in the first layer of the host matrix, such that the host matrix comprises the first subset of quantum dots selected to emit red secondary light and the second subset of quantum dots selected to emit green secondary light dispersed in the same layer, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source; or (b) the first subset of quantum dots selected to emit red secondary light is dispersed in the first layer of the host matrix, and the host matrix further comprises a second layer comprising the second subset of quantum dots selected to emit green secondary light dispersed therein, wherein the first layer is disposed to allow the green secondary light from the second layer to pass therethrough, wherein the first layer and the second layer are adjacent to one another, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source. (a) both the first subset and the second subset of quantum dots are dispersed in the first layer of the host matrix, such that the host matrix comprises the first subset of quantum dots selected to emit red secondary light and the second subset of quantum dots selected to emit green secondary light dispersed in the same layer, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source; or (b) the first subset of quantum dots selected to emit red secondary light is dispersed in the first layer of the host matrix, and the host matrix further comprises a second layer comprising the second subset of quantum dots selected to emit green secondary light dispersed therein, wherein the first layer is disposed to allow the green secondary light from the second layer to pass therethrough, wherein the first layer and the second layer are adjacent to one another, wherein the white light comprises the red secondary light, the green secondary light, and said blue light emitted by the primary light source.