Experimental investigation on thermal performances of SMD LEDs light bar: Junction-to-case thermal resistance and junction temperature estimation

Abstract

In this present work, the heat sink thermal resistance, junction-to-case thermal resistance and junction temperature of SMD LEDs light bar module are determined using luminous flux measurements and photo-electro-thermal (PET) theory equations, proposed as original investigation. The obtained results showed that junction temperature increases with the electrical input power supply, which affects the luminous flux efficacy of investigated SMD LEDs light bar. Thus, we noticed the luminous efficacy fall, which it passes from 27.18 lm/W at 0.25 W to 7.51 lm/W at 2 W, while the total luminous flux increases until reach a maximum value of about 15.26 lm at 1.5 W which the spectral radiant flux of LEDs light bar remains higher. The junction-to-case thermal resistance Rjc increases with the input power until reaches a value of about 60 °C/W for 1 W, after Rjc decreases for higher input power (i.e. 2 W). Thus, the junction temperature Tj for SMD LEDs light bar is estimated for different injected powers Pd; Tj passes from 31.33 °C to 98.11 °C at Tamb of 23 °C, as Pd increases from 0.25 W to 2 W. In addition, these first results remain a starting point to study an advanced lighting system based on this type of LEDs in our future works.