Research on effect of centrifugal speed on the light color characteristics of COB light source and its mechanism

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.