Patent ID: 7897987

Claim:
A light-emitting device, comprising: a light-emitting diode; and a plurality of stacked phosphor layers, each of the phosphor layers being configured to emit light having a color different from a color of light emitted from another phosphor layer, and a stacking sequence of the plurality of phosphor layers being a sequence such that phosphors constituting the phosphor layers do not interact with each other, wherein among the phosphor layers, any two phosphor layers A and B that do not interact with each other are arranged in such a manner that the phosphor layer A is further from the light-emitting diode than the phosphor layer B when a discriminant D>1 and that the phosphor layer B is further from the light-emitting diode than the phosphor layer A when the discriminant D<1, and the discriminant D is given by D=k B +( kA−k B )/ B +(1− k A )/ AB where k A represents a rate of reduction in a conversion efficiency of the phosphor layer A when the stacking sequence of the phosphor layers A and B is changed from a stacking sequence of the phosphor layers A and B to a stacking sequence of the phosphor layers B and A in order of increasing distance from the light-emitting diode; k B represents a rate of reduction in a conversion efficiency of the phosphor layer B when the stacking sequence of the phosphor layers A and B is changed from the stacking sequence of the phosphor layers A and B to the stacking sequence of the phosphor layers B and A in order of increasing distance from the light-emitting diode; A represents a ratio of an intensity of excitation light transmitted through the phosphor layer A to an intensity of excitation light incident on the phosphor layer A; and B represents a ratio of an intensity of excitation light transmitted through the phosphor layer B to an intensity of excitation light incident on the phosphor layer B, with a proviso that each of the phosphor layers A and B has a phosphor content such that an emission intensity is unchanged when the stacking sequence of the phosphor layers A and B is changed.