The thermal resistance of a material is its resistance against thermal conduction. The unit of thermal resistance is degree per watt, representing the temperature difference across a structure when a unit of heat energy flows through it in a unit time. After the LED is lighted and the thermal conduction stabled, as every watt of power on the chip surface being consumed, the temperature difference between the PN junction and the linking bracket or heating panel is the thermal resistance value of the LED. The thermal resistance value is most often represented as θ or R; the temperatures of the joint face and of the point to which the heat has been conducted as Tj and Tx respectively, and the heating output as P. The higher the thermal resistance value is, the more difficult the heat is being conducted, and thus higher component temperatur. From the thermal resistance value, the heating condition of the component can be decided or estimated. The lower the thermal resistance value is, the faster the chip dissipates heat. Therefore, to lower the temperature of the PN junction in the chip is helpful to lengthen the lifespan of LED.

What are the main factors influencing the thermal resistance value of LED components? And how can its influence be decreased?

1. Thermal resistance of a LED chip is related to its structure and the original material. Therefore, it is crucial to decrease the thermal resistance value of the LED itself.
2. Different thermal conductivities of copper, aluminium, or other heat sink materials can also influence the thermal resistance of LED. So, choosing the appropriate heat sink material helps decrease the thermal resistance of LED components.
3. Even in condition of applying the same heat sink material, the size of the cooling area is also directly related to the LED thermal resistance. The well-designed and large-sized second-time cooling system will decrease the thermal resistance and can be helpful to increase the lighting efficiency and lengthen the life-span of the LED.
4. LED thermal resistance value can be influenced by: whether the LED chip is joined by the thermal conductive glue,  connected directly to the metal, and the kind of the glue or metal used. The thermal resistance of the joint face between the LED and the second-time cooling system should be kept as low as possible.
5. The temperature of the operational environment can also affect the thermal resistance of the LED component. The suggestion is to keep the surrounding temperature as low as possible.
6. Pay attention to some technological details such as adopting right materials and controlling the rated power input. Improve the cooling system of the LED with the precondition of increasing its lighting efficiency and life-span.

Summary

We must take the following points into consideration when designing LED components:

1.Decrease the thermal resistance value of the chip.
2.Optimize the thermal conducting passage.
a.Passage infrastructure: Length: the shorter the better; Size: the larger the better; the fewer segments the better; eliminate the thermal conducting bottleneck in the passage.
b.The higher the thermal conductivity value λ of the passage material the better.
c.Improve the packaging technology to make the linking between the segments tighter and more reliable.
3.Enhance the thermal conducting function.
4.Adopt the optical passage materials of higher thermal conductivity.