A huge market for LEDs is in luminaires for general lighting. Using LED luminaires instead of incandescent luminaires or fluorescent luminaires has well known energy benefits as well as overall quality-of-light benefits.
It is well known to couple LEDs to a narrow edge of a transparent acrylic light guide and roughen the light output surface of the light guide, or provide microlenses on the surface of the light guide, to allow the light to leak out the large surface of the light guide. Total internal reflection (TIR) keeps the light in the light guide until the light impinges on the surface feature at less than the critical angle for exiting the light guide. For example, LED luminaires have been optically coupled to the edges of an acrylic sheet with etched patterns for display signage and for backlighting applications. The advent of high power LEDs in the late 1990's prompted increased implementations of this technology by virtue of the much higher flux densities available from these more powerful and efficient LEDs.
The light guide may be used as a ceiling panel to provide general lighting for a room. Such luminaires have emission patterns that are difficult or impossible to optimize for overhead general lighting where glare (direct view by observers) and industry requirements dictate the emission specifications for such lighting.
Color and brightness uniformity is a desired feature in such overhead lighting. Color uniformity is difficult when using a plurality of phosphor-converted LEDs that generate white light. This is because LEDs, even from a single wafer, have a range of peak wavelengths, and it is difficult to provide the optimal phosphor combinations and uniformity of application process to cause all the LEDs to output light having the same chromaticity (e.g., white point, or correlated color temperature, or spectral power distribution).
Therefore, what is needed in the lighting industry is a solid-state luminaire that overcomes at least one of the deficiencies of the state-of-the art.
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