Impact of Electronics Over Localized Hot Spots in Multi-Chip White LED Light Engines

In recent years, demand towards high power white LEDs has risen significantly covering a wide range of application areas. While many industries prefer more light extraction using less number of LED chips on their luminaires, the compact nature of the LED package poses some challenges for controlling junction temperatures of LEDs. Junction temperature measurement capabilities are limited to more simple measurements of board temperatures with added disadvantages of expensive measurement techniques. Although many studies focused on optothermal characterization of single LEDs, a few studies analyzed the junction temperatures of individual LEDs and their impacts on optical properties in multi-LED systems. Thus, this study introduces a new approach towards Forward Voltage Change Method and uses Integrating Sphere System to characterize thermal and optical traits of white multi-LED systems operating at different electrical conditions. Results show that additional electronic components in a multi-LED system can induce considerable thermal issues since it was determined that heat loads may reach up to total radiant power of LEDs and can decrease the conversion efficiency of a lighting unit by 6.1%. It was also shown that junction temperatures of LEDs can be affected by thermal conditions over the circuit and they need to be determined individually. Thus, a junction temperature measurement technique is introduced in this study for multi-chip LED systems enabling a high functionality in future studies for developing better cooling techniques and more lumen extraction.