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We apply a microstructure array (MSA) film to improve the angular color uniformity (ACU) of a correlated-color-temperature-tunable LED (CCT-tunable LED) with tunable CCT ranging from 2700 to 6500 K. The effects of the MSA film area and the height between the film and LED are investigated and optimized. The resulting ACU is greatly improved for all CCT ranges with little luminous flux loss. For a typical CCT range of 3000-4000 K, with a full-covering MSA film and height H = 5 mm, the CCT deviation is significantly reduced from 1090 K to 218 K, with only 1.8% luminous flux loss.
Qiu et al. (Fri,) studied this question.