"As demand for better lighting devices continues to increase, it would be desirable to provide cost-effective LED-based lighting sources having improved efficiency and brightness."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "Even though conventional LED-based white light sources have found wide application, they suffer from many limitations. One common problem is that conventional LED-based white light sources suffer from thermal instability of the phosphor and often do not provide sufficient and reliable brightness. As described in more detail below, conventional LED-based lighting devices tend to degrade as the devices heat up, and thermal management problems worsen with high power LEDs that are increasingly in demand.
"In various embodiments, the present invention provides methods and devices in which light-conversion material is present only on the top surface of an LED die, leaving the side surfaces of the LED substantially free from the light-conversion material. In an embodiment, the method includes using a syringe or a similar device to deposit a small amount of viscous light-conversion material that includes a high concentration of wave-shifting material, such as phosphor. This deposition method allows a high concentration of large phosphor particles in the light-conversion material. Moreover, the phosphor particles can settle and be disposed close to the LED die, and the temperature of the phosphor can be controlled by the heat sink associated with the LED die. As a result, light apparatus providing brighter, more stable, and more uniform light can be made at reduced cost.
"Even though the invention has been applied to LED-based white light sources, it would be recognized that the invention has a much broader range of applicability. For example, various combinations of phosphor and light source having different colors can be used to produce a substantially uniform light of a desired color or a combination of light having multiple colors.
"According to an embodiment of the present invention, a method for making a lighting apparatus includes providing a substrate and disposing a light-emitting diode overlying the substrate. The light-emitting diode has a top surface oriented away from the substrate and a plurality of side surfaces. A light-conversion material is provided that includes a substantially transparent base material and a wave-shifting material dispersed in the base material. The concentration of the wave-shifting material can be at least 30%. In an embodiment, the concentration of the wave-shifting material can be approximately 50%. A predetermined amount of the light-conversion material is deposited on the top surface of the light-emitting diode while the side surfaces are maintained substantially free of the light-conversion material.
"In a specific embodiment of the above method, the wave-shifting material is allowed to settle to a bottom portion of the light-conversion material on the top surface of the light-emitting diode, thus forming a uniform layer of wave-shifting material overlying the top surface of the LED. In an embodiment, the substrate has a recess in a front side of the substrate, and the light-emitting diode is disposed in the recess. In a specific embodiment, the wave-shifting material comprises particles having an average diameter of 2 .mu.m or larger. In some embodiments, the light-conversion material is deposited using a syringe or a needle. In certain embodiments, the method also includes subjecting the substrate, the light-emitting diode, and the light-conversion material to a curing process.
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