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When the COB packaging LED light source is prepared by the centrifugal precipitation process, the phosphor forms a high-density phosphor layer on the chip surface. Centrifugal speed can change the vertical distribution of different kinds of particles in the phosphor coating, which affects the color parameters of the LED light source. Several different centrifugal speeds are used, the luminous flux of the sample has increased by about 5%, and the color temperature of the light source is also rising. The color temperature increases with the addition of the rotating speed, and the color temperature adds up to 278.6 K at 500 r/min and 422.4 K at 1000 r/min. The first reason for this phenomenon is that the proportion of large particles at the bottom of the phosphor layer formed by centrifugal precipitation (close to the chip) increases, which increases the conversion efficiency of phosphor. Second, after the powder is precipitated, a phosphor thin layer composed of very small particles will be formed on the upper surface of the phosphor layer. The higher the rotational speed, the thinner this thin layer, the smaller the absorption effect on the short-wave part of the spectrum, and the overall color temperature of the light source increases slightly. Third, the proportion of high-density yellow-green powder at the bottom of the phosphor layer formed by the centrifugal precipitation process is higher, and the photoluminescence produces a yellow-green band. [ABSTRACT FROM AUTHOR]

Based on the fact that flip chip without front-side bonding wire, a correlated color temperature (CCT) tunable chip on board (COB) light emittin g diodes (LED) light source was fabricated, by screen printing technology before the phosphor was coated on the whole luminous surface. A part of the blue LED chips in the light source excites the fluorescent glue to produce a warm white light (CCT = 2631 K), and the other part produces cool white light (CCT = 6181 K). When changing the driving current ratio of the two parts of the chips, the CCT of COB LED light source can be continuously adjusted between warm and cool white light. According to the measured data, the relationship between the CCT and the current ratio of the two parts is obtained by fitting. Within the tunable range of the CCT (2631 K to 6181 K), the color rendering index (CRI) is about 90. The minimum is 89.3 and the maximum is 93.1. While achieving tunable CCT and high CRI, the LED light source has a luminous flux of 1938.76 lm on a circular surface with a diameter of 11 mm. The overall luminous efficiency is close to 100 lm/W. [ABSTRACT FROM AUTHOR]