The correct LED heat sinks must be determined for new LED lighting designs. The approach of integral models and verification test discussed here give an insight into the functional integrity and operational reliability of design in meeting market expectations.
Each LED has its set of parameters. Ambient temperature is one of the parameters. Different lights require different temperatures. Mounted, open air spotlights need 30ᵒ C, recessed ceiling lights 50 to 55ᵒ C, and automotive lighting 45ᵒ C.
The parameters must be defined. The LED Chips on Board module manufacturers provide lifetime expectations under conditions that are ideal. They calculate 90 percent reliability for the maximum junction temperature.
In calculating the required LED heatsinks, it must be understood that each part of a design adds heat due to the material’s thermal resistance. The total design should be below the maximum junction temperature required.
A mathematical calculation is made to define the maximum thermal resistance heat sinks should have or the maximum rise in temperature LED heatsinks create when dissipating power. Thermal resistance is expressed as a Rth value. Some manufacturers give thermal resistance value for heat sinks that are independent of dissipation power and ambient temperature. The Rth value of LED heatsinks is not the same under all conditions.
After applying thermal pads and heat sinks, verify the design. Manufacturers include safety margins in their designs. A maximum of 97.4ᵒ C thermal measurement point should not be subjected to temperatures more than the range of 87 to 92ᵒ C.
All high power LEDs need to dissipate the heat produced to keep it below the maximum operating temperature. Overheating can cause a shortened life, a reduction in light output, an output color change, or complete LED failure.
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