Flexible selection of LED bulb heat dissipation treatment to meet actual application needs

When the operating temperature of LED bulbs increases, their lifespan and luminous efficiency will decrease, and the degree of color deviation and light decay will increase, which will have a considerable adverse effect on LED lighting . Therefore, how to dissipate heat in the most efficient way within the limited space of LED bulbs has long been the focus of LED lighting industry research and development.

Generally speaking, the waste heat generated by the diode in the LED bulb when it emits light will be discharged into the surrounding atmosphere after being guided by multiple components such as Slug, Board, etc. The heat transfer between the diode and Slug, Slug and Board mainly relies on heat conduction. As for the transfer from the Board to the atmosphere, there are three types of heat conduction, heat convection and heat radiation. When planning the heat dissipation design of the product, LED lighting companies can first perform a heat dissipation analysis on this conduction process to calculate the thermal resistance value in each link, and then improve the parts with poor performance. This approach to solving the heat dissipation problem will be more effective.

Analyze the form of heat conduction to solve LED heat dissipation

Taking the improvement of heat conduction efficiency as an example, we can try to increase the geometric size area of ​​slug/board, or directly use high thermal conductivity materials to make heat dissipation components to reduce the thermal resistance of this part. As for the diffusion thermal resistance problem derived from the difference in area size and uneven temperature distribution between diode and slug, slug and board, Jian Guoxiang suggested that we can start from reducing the area ratio, increasing the thickness of the component base, improving the thermal conductivity of the material itself, and strengthening the heat convection effect. Increasing the thickness of the base is a more common practice. When its thickness increases, the difference effect caused by the area ratio can be reduced, and the speed of heat diffusion in the vertical direction and horizontally to the sides will be more consistent, thereby reducing the impact of its diffusion thermal resistance problem.

If the thickness of the base cannot be increased due to space considerations, the industry may also be able to increase the lateral thermal conductivity of the base by adding heat pipes, etc., to shorten the difference in vertical and horizontal thermal conduction. This means that when the base thickness is thin, the benefit of increasing its lateral thermal conductivity is higher. Although increasing the thickness will reduce the diffusion thermal resistance, it will also increase the one-dimensional thermal resistance value. The industry must try to strike a balance between the two through experiments and calculations to find the best thickness for the bottom. But generally speaking, when the area difference between the diode and the slug, and between the slug and the board is larger, the optimal thickness will tend to increase accordingly.

As for thermal convection, in addition to the use of fans and other methods to force convection due to the needs of the environment, general manufacturers usually use natural convection to avoid increasing the volume of their product's heat dissipation components and manufacturing costs. The larger the geometric area of ​​the board or the higher the thermal convection coefficient, the smaller the thermal resistance of the thermal convection. Unfortunately, the larger the geometric area of ​​the board, the worse the thermal convection coefficient. Therefore, when planning the layout of LED bulbs, people generally take the maximum value of the geometric area of ​​the board multiplied by the thermal convection coefficient for design.

In addition, for the design of the heat sink fins, since the heat will be dissipated from the bottom to the tail end, its thermal conductivity coefficient, thermal convection coefficient and thickness will affect the optimal size of the heat sink fins. In general, when the thickness and thermal conductivity of the heat sink fins are higher, the fin heat dissipation efficiency will be better; and relatively speaking, when the thermal convection coefficient is higher, the fin heat dissipation efficiency will be worse. In other words, if the thermal convection effect is very good, the required size of the heat sink fins will be smaller. Therefore, the heat sink fins that generally use natural convection are usually taller, and the distance between the fins should be wider.

LED bulb heat dissipation needs to meet actual application requirements

In addition to the above-mentioned heat conduction and convection, heat radiation is also an important mechanism for LED bulbs to dissipate heat. The effect of heat radiation is related to the surface condition of the material. Take the heat sink fins as an example. Under the condition of fixed size and spacing, whether the aluminum surface is polished or oxidized will have a great difference in its heat radiation effect. On the other hand, because the heat radiation surfaces must have a temperature difference and can directly see each other in order to conduct heat transfer, for some styles of lamps, the heat dissipation effect of heat radiation is sometimes even better than the other two.

Different lamp designs and lighting requirements will require different heat dissipation technologies. Variables such as luminous efficiency, semiconductor materials, light source distribution, heat transfer distance, external airflow environment, etc. have a great impact on the design of lamp heat dissipation components. For example, if the luminous efficiency of LED bulbs can be increased to 90%, the heat converted into current can be reduced, or the semiconductor component materials used can still operate normally at higher temperatures, the area occupied by the heat dissipation components can naturally be reduced. "Some lamps (such as recessed lights) will be in a relatively closed space, while some (such as spotlights) can be directly exposed to the atmosphere or cold room environment." Therefore, the specific design method of LED bulb heat dissipation treatment should depend on its needs and the situation.