Detailed Study of Optical and Thermal Performance for White Light-Emitting Diodes With Filament-Like Packaging Structures

Retro filament white light-emitting diodes (WLEDs) have attracted great attention and are widely welcomed by consumers. The results of an investigation for the optical and thermal performance of filament-like WLEDs with various packaging structures are presented in detail. The optical simulation shows that the phosphor concentration on the chip-bonding side makes a great contribution to increasing backscattered blue light power. It means the backside should be packaged to improve blue light utilization. By controlling the phosphor coating structure, several filament-like LEDs were fabricated and subsequently investigated. The luminous efficacy (LE), correlated color temperature (CCT) and thermal reliability were measured, and then the structures were proposed and optimized. The optimal structure can maintain the equivalent LE compared with others under almost the same CCT. The CCT and light intensity spatial distribution were also analyzed based on the phosphor structure. The phosphor on the chip-bonding side contributes significantly to the CCT deviation. Consequently, the proposed structure filament-like WLEDs exhibited 2.23 and 5.42 degrees lower working temperatures than the half packaging and full packaging structures under a driving current of 15 mA, respectively. Besides, the no-middle packaging structure was investigated in detail for optimal optical performance. After optimization, when the back surface dispensed 20 mu L of phosphor resin, the LE increased from 182.9 to 188.3 lm/W at similar CCT with the CCT deviation changed from 1062 to 154.5 K significantly. Therefore, it was revealed that optimizing the packaging structure is an efficient method of enhancing the performance of filament-like WLEDs.