1. Field of the Invention
This invention relates generally to light emission devices incorporating multiple solid state emitters (e.g., light emitting diodes (LEDs)) and/or multiple phosphors as emissive components.
2. Description of the Related Art
In the illumination art, a variety of approaches have been employed to produce light of desired spectral character.
LEDs have come into widespread usage as a result of their advantages, which include small size, long life, low energy consumption, and low heat generation.
U.S. Pat. No. 6,513,949 issued Feb. 4, 2003 describes a hybrid lighting system for producing white light, including at least one LED and a phosphor-LED, in which the color and number of the LEDs and/or the phosphor of the phosphor-LED may be varied.
U.S. Pat. No. 6,600,175 issued Jul. 29, 2004 describes a light emitting assembly including an LED emitting a first, relatively shorter wavelength radiation, and a down-converting luminophoric medium, e.g., phosphoric medium, that in exposure to such first radiation, responsively emits a second, relatively longer wavelength radiation.
White LED devices have been commercialized that utilize a blue LED and a YAG phosphor (Y3Al5O12 doped with cerium) that partially absorbs blue radiation (centered on 470-480 nm) from the blue LED and emits light having a broad wavelength range with a dominant yellow characteristic (centered on ˜550-600 nm).
The commercially available LED/phosphor devices for production of white light do not provide high conversion efficiency color rendering in various spectral regimes of interest. For example, in many applications, consumers prefer white light having color (as quantifiable by color temperature and color rendering index values) that matches sunlight, conventional incandescent bulb light, or fire light such as candle light.
There is accordingly a continuing need in the art for efficient LED/phosphor illumination systems producing light having a color rendering that closely matches a predetermined spectral distribution.