Formation of Coated Phosphor Layers by Rotation–Revolution for Remote-Phosphor LED Bulbs and Characterization of LED Light Bulb With Super High Color Rendition

We have developed a new system for coating phosphor globes used in remote-phosphor-type light-emitting diode (RP-LED) bulbs. The system has a rotation-revolution coating apparatus and a heating unit. After dispensing a phosphor slurry mixed with phosphor powder and silicone resin into globes, the phosphor slurry is uniformly coated on the entire inner surface of the globes by the coating system. The phosphor slurry is then cured. We obtained phosphor globes having a phosphor layer with a uniform thickness on the entire inner surface of the globes. We prepared RP-LED bulbs combined with an LED chip-on-board (COB) that emitted light with a wavelength of 400 nm, and phosphor globes containing red, green, and blue phosphor powders obtained using the coating system. The bulbs have a high color rendering because their spectrum is almost the same as that of blackbody radiation. The RP-LED bulbs having a phosphor layer with uniform thickness had more uniform chromaticity and luminescence distribution than an RP-LED bulb having a phosphor layer with nonuniform thickness. The total luminous flux of the RP-LED bulbs was 29% higher than that of a bulb mounted on a COB covered with a phosphor layer. Furthermore, the semiangle at half-power of the RP-LED bulbs was much larger than that of the bulbs mounted on a COB with a phosphor layer.