What’s the definition of ‘thermal resistance’ value in a LED and how to interpret it?
According to the internet it’s a difference in temperature between emitter’s outer surface (obviously thermal pad) and led’s p-n junction per every watt.
If you feed SFT40 with 25 watts of energy and the mcpcb (right under the emitter) has a temperature of 70C then the led’s junction is heated up to 70 + 0.7*25 = 87.5C (roughly as the mcpcb itself has a thermal resistance).
The better the LED’s casing removes heat from led the lower the temperature difference and thus thermal resistance is.
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