A light source having emissions in a plurality of spectral bands. The simplest light source according to the present invention is constructed from first and second light sources and a dichroic beam splitter. The first and second solid state light sources emit light in first and second bands of non or only partially-overlapping wavelengths. The dichroic beam splitter combines light from the first and second solid state light sources by passing light in the first band while reflecting light in the second band to generate light having a spectral content in the first and second bands. The solid state light sources are preferably arrays of LEDs, VCSELs, or edge emitting semiconductor lasers. A light source having improved radiance in the green region of the spectrum can be constructed by utilizing first and second solid state light sources that emit in different bands in the green portion of the spectrum. A white light source can be constructed by utilizing a third solid state light source and a second dichroic beam splitter and by choosing the emission bands of the light sources such that light leaving the second dichroic beam splitter is perceived as white by an observer when all three solid state light sources are emitting light. This light source has a radiance that is higher than the radiance of each individual solid state light source.
A light emitting device comprises a light emitting diode that emits primary light and a SrGa.sub.2 S.sub.4 :Eu.sup.2+ phosphor material capable of absorbing at least a portion of the primary light and emitting secondary light. The secondary light includes a wavelength longer than a wavelength of the primary light.
Provided are an illumination optical system having superior color rendering properties while ensuring sufficient illuminance, an image display apparatus comprising the illumination optical system and a spatial modulation device illuminated by the illumination optical system, and a method of illuminating the spatial modulation device. A first light source (11), a second light source (21) having a different emission spectrum from an emission spectrum of the first light source (11), and a replacement optical system replacing light in a specific waveband in a luminous flux (L1) from the first light source (11) with a luminous flux (L2) from the second light source (21) are comprised, and the light in the specific waveband with weak light intensity in the luminous flux (L1) from the first light source (11) is replaced with the luminous flux (L2) with sufficient intensity from the second light source (21). Thereby, a white balance can be kept without reducing the illuminance more than necessary, and superior color rendering properties can be exhibited.
A method of fabricating a light emitting device includes providing a light emitting diode that emits primary light, and locating proximate to the light emitting diode a (Sr.sub.1-u-v-x Mg.sub.u Ca.sub.v Ba.sub.x)(Ga.sub.2-y-z Al.sub.y In.sub.z S.sub.4):Eu.sup.2+ phosphor material capable of absorbing at least a portion of the primary light and emitting secondary light having a wavelength longer than a wavelength of the primary light. The composition of the phosphor material can be selected to determine the wavelengths of the secondary light. In one embodiment, the light emitting device includes the phosphor material dispersed as phosphor particles in another material disposed around the light emitting diode. In another embodiment, the light emitting device includes the phosphor material deposited as a phosphor film on at least one surface of the light emitting diode.
A light-emitting device comprises a substrate, electrical terminals disposed on a top side of the substrate, and a light-emitting semiconductor device disposed above the substrate. The light-emitting semiconductor device has a bottom side oriented to face toward the top side of the substrate. Electrodes are disposed on the bottom side of the light-emitting semiconductor device and electrically connected to the terminals on the substrate. A glass layer is arranged in a path of output light emitted by the light-emitting semiconductor device. The glass layer contains fluorescent material that converts at least a portion of the output light to converted light having a wavelength different from a wavelength of the output light. The fluorescent material may include SrS:Eu.sup.2+ that emits red light and (Sr, Ba, Ca)Ga.sub.2 S.sub.4 :Eu.sup.2+ that emits green light.
A white-light emitting diode (LED) is provided that emits primary light at a wavelength that is in the range of 485 to 515 nanometers (nm), which corresponds to a bluish-green color. A portion of the primary light is converted into a reddish-colored light that ranges in wavelength from approximately 600 to approximately 620 nm. At least a portion of the converted light combines with the unconverted portion of the primary light to produce white light. A number of phosphor-converting elements are suitable for use with the LED, including a resin admixed with a phosphor powder, epoxies admixed with a phosphor powder, organic luminescent dyes, phosphor-converting thin films and phosphor-converting substrates. Preferably, the phosphor-converting element is a resin admixed with a phosphor powder in such a manner that a portion of the primary light impinging on the resin is converted into the reddish-colored light and a portion of the primary light passes through the resin without being converted. The unconverted primary light and the phosphor-converted reddish-colored light combine to produce white light. The LED is mounted in a reflector cup that is filled with the phosphor-converting resin. The LED may be mounted in either a normal or flip-chip configuration within the reflector cup.
