Here, we have to follow some specific formulas. We need to take care of the following items:
· Individual Thermal resistance of each part.
· The formula used can be = T = Pd * Rth
· Here, we can calculate thermal resistance by using formula (Rj-c).
· In case of recessed environment, Temperature should be 45 Degree.
· The total power to dissipate should be less than total power of LED consumes.
· More light the power would be, more efficient your LED module would be.
· Maximum Temperature can be calculated as Tj- Ta = 135-45 = 90 Degree.
· Pd= 14.7 W*80 % =11.76 W.
· Heat sink with Rth value should be less than 4.65 Degree.
Once you are done with the applying thermal pad and the heat sink, you have to verify the design. We have to keep some safety precautions prior design. Maximum Temperature limit should not be more than 100 degree centigrade. But for safety precaution we have to measure the temperature around 87-92 degree centigrade.
As far as the Rth value is concerned, some manufacturers give a single thermal resistance for the heat sink. But you should be well aware of Rth of the same heat sink.