And the thermal resistance formula is.

The thermal resistance of power LED with or without heat sink.

 

       

 

 

 

 

Measure the thermal resistance of a red 12 inch traffic light.

This 12” red ball have 104 5 mm LEDs in 4 strings. Each string consists of 26 LEDs in series and the voltage is 58.7 volts. Total supply current is 103mA which makes the LED current 26mA.

The luminous output is specified at 358 cd and total power is rated 7.9W.