What is the LED thermal resistance?

1.LED thermal resistance

Thermal resistance is the resistance of heat flow through an object. Is determined by the nature of the material. The thermal resistance is proportional to the heat flow through the path length and inversely proportional to the cross-sectional area of the path and inversely proportional to the thermal conductivity of the material. That is:

Rth=L/S lambda

2 distinguish between the internal thermal resistance and the external thermal resistance

Internal thermal resistance

The internal thermal resistance of the light source is also known as the package thermal resistance:

(1) the thermal resistance of LED chip material, RL1.

(2) chip and substrate (heat sink) adhesive thermal resistance, RL2.

(3) substrate heat conduction resistance RL3,

(4) encapsulating colloid thermal resistance, RL4.

(5) thermal resistance of lens, RL5.

External thermal resistance:

(1) the thermal resistance of the heat conducting layer on the bottom of the heat sink, RO1.

(2) thermal resistance of copper clad laminate, RO2.

(3) thermal insulation resistance between copper clad plate and aluminum substrate, RO3.

(4) aluminum substrate thermal resistance, RO4.

(5) the thermal conductivity of the thermal conductivity between the aluminum substrate and the heat sink is RO5.

(6) heat sink resistance, RO6.

Application of light source is the internal thermal resistance of thermal resistance, which is related to the light and life is an important indicator to measure the quality of a light source, the lamp is unable to change the user, i.e. system design at. The light effect of the system is inversely proportional to the thermal resistance of the system, and the lower the thermal resistance, the higher the luminous efficiency.

3 measure the thermal and optical properties of the system with the ratio of steady state and transient light efficiency

At present, the country has not yet introduced LED light thermal resistance measurement standard, usually in accordance with the thermal resistance measurement method of semiconductor device using ordinary voltage measurement method, to measure K value, then calculate out a position to the PN junction resistance. Spectral method, optical thermal resistance scanning method and optical power method. Due to the complexity of the measurement process, it is difficult to regulate, it is still not widely used. People from the heat transfer into the LED "resistance" is a word only hope to find the light sources and lamps by measuring the temperature rise of each node, so that the light source temperature design work in a safe range, reduce LED decay. In fact, the purpose of testing the junction temperature and thermal resistance is to compare the performance of the heat transfer system, in order to optimize the heat / cost ratio, which does not need to beat around the Bush to repeatedly measure and calculate, the operation is not accurate enough. I suggest that as long as the temperature difference of the heat transfer path in the LED lighting system can be measured to show the thermal resistance between them, that is, the "node temperature difference" to understand the "thermal resistance". In this paper, we propose to measure the optical and thermal properties of the system with the ratio of steady state and transient light efficiency. Measurement methods: first, measuring out transient light effect. When the system enters the heat stability, light intensity, temperature rise no longer no longer falling and relatively stable after the measured steady light efficiency, steady light light efficiency is divided by the transient steady light effect and transient light effect ratio, according to the thermal resistance is inversely proportional to the relationship with the light effect, the ratio of size can be seen in different lights the system light efficiency or quality of resistance, usually pay attention to exclude the impact of power supply measurement. For example: two different street A and B, respectively, to determine their transient light effect and steady light efficiency ratio, A=95%, B=90%, A B can be identified in this test method is simple and easy to operate, the author suggests that through discussion and improvement of the measurement method is recommended to regulate the industry measurement and technical standards.