On the determination of the temperature distribution within the color conversion elements of phosphor converted LEDs.

We present an iterative optical and thermal simulation procedure which enables the determination of the temperature distribution in the phosphor layer of a phosphor converted LED with good accuracy. Using the simulation both the highest phosphor temperatures, which are mostly relevant to material degradation as well as the temperatures of those phosphor particles which mainly contribute to converted light emission can be determined. We compare the simulations with experimental studies on the phosphor temperature. While infrared thermography only gives information on the phosphor layer surface temperature, phosphor thermometry provides temperature data on the volume temperature of the phosphor layer relevant to color conversion.

The impact of the non-linearity of the radiant flux on the thermal load of the color conversion elements in phosphor converted LEDs under different current driving schemes.

For a systematic approach to improve the reliability and the white light quality of phosphor converted light-emitting diodes (LEDs) it is imperative to gain a better understanding of the individual parameters that affect color temperature constancy and maintenance. By means of a combined optical and thermal simulation procedure, in this contribution we give a comprehensive discussion on the impact of different current driving schemes on the thermal load of the color conversion elements (CCEs) of phosphor converted LEDs. We show that on the one hand a decreasing duty cycle under pulse width modulation driving conditions may cause a notable temperature variation and on the other hand also effects due to the non-linearity between the blue radiant flux and the current have to be considered for the thermal load of the CCEs.