LED, also known as the fourth generation lighting source or green light source, has the characteristics of energy saving, environmental protection, long lifespan, and small size. It is widely used in various fields such as indication, display, decoration, backlight, general lighting, and urban night scenes. According to different usage functions, it can be divided into five categories: information display, signal lights, automotive lighting fixtures, LCD screen backlight, and general lighting.
Conventional LED lights have shortcomings such as insufficient brightness, which leads to insufficient popularity. Power type LED lights have advantages such as high brightness and long service life, but they have technical difficulties such as packaging. Below is a brief analysis of the factors that affect the light harvesting efficiency of power type LED packaging.

1. Heat dissipation technology
For light-emitting diodes composed of PN junctions, when forward current flows through the PN junction, the PN junction experiences heat loss. This heat is radiated into the air through adhesive, encapsulation materials, heat sinks, etc. During this process, each part of the material has a thermal impedance that prevents heat flow, known as thermal resistance. Thermal resistance is a fixed value determined by the size, structure, and materials of the device.
Assuming the thermal resistance of the light-emitting diode is Rth (℃/W) and the heat dissipation power is PD (W), the temperature rise of the PN junction caused by the heat loss of the current is:
T (℃)=Rth&TImes; PD
The PN junction temperature is:
TJ=TA+Rth&TImes; PD
Among them, TA is the ambient temperature. Due to the increase in junction temperature, the probability of PN junction luminescence recombination decreases, resulting in a decrease in the brightness of the light-emitting diode. Meanwhile, due to the increase in temperature caused by heat loss, the brightness of the light-emitting diode will no longer continue to increase proportionally with the current, indicating a phenomenon of thermal saturation. In addition, as the junction temperature increases, the peak wavelength of the emitted light will also shift towards longer wavelengths, about 0.2-0.3 nm/℃. For white LEDs obtained by mixing YAG fluorescent powder coated with blue light chips, the drift of blue light wavelength will cause a mismatch with the excitation wavelength of the fluorescent powder, thereby reducing the overall luminous efficiency of white LEDs and causing changes in white light color temperature.
For power light-emitting diodes, the driving current is generally several hundred milliamps or more, and the current density of the PN junction is very high, so the temperature rise of the PN junction is very significant. For packaging and applications, how to reduce the thermal resistance of the product so that the heat generated by the PN junction can be dissipated as soon as possible can not only improve the saturation current and luminous efficiency of the product, but also enhance the reliability and lifespan of the product. In order to reduce the thermal resistance of the product, the selection of packaging materials is particularly important, including heat sinks, adhesives, etc. The thermal resistance of each material should be low, which requires good thermal conductivity. Secondly, the structural design should be reasonable, with continuous matching of thermal conductivity between materials and good thermal connections between materials to avoid heat dissipation bottlenecks in the thermal channels and ensure heat dissipation from the inner to the outer layers. At the same time, it is necessary to ensure from the process that heat is dissipated in a timely manner according to the pre designed heat dissipation channels.

2. Selection of filling adhesive
According to the law of refraction, when light is incident from a dense medium to a sparse medium, full emission occurs when the incident angle reaches a certain value, that is, greater than or equal to the critical angle. For GaN blue chips, the refractive index of GaN material is 2.3. When light is emitted from the inside of the crystal towards the air, according to the law of refraction, the critical angle θ 0=sin-1 (n2/n1).
Among them, n2 is equal to 1, which is the refractive index of air, and n1 is the refractive index of GaN. Therefore, the critical angle θ 0 is calculated to be about 25.8 degrees. In this case, the only light that can be emitted is light within the spatial solid angle of ≤ 25.8 degrees. According to reports, the external quantum efficiency of GaN chips is currently around 30% -40%. Therefore, due to the internal absorption of the chip crystal, the proportion of light that can be emitted outside the crystal is very small. According to reports, the external quantum efficiency of GaN chips is currently around 30% -40%. Similarly, the light emitted by the chip needs to pass through the packaging material and be transmitted to space, and the impact of the material on the light harvesting efficiency also needs to be considered.
Therefore, in order to improve the light harvesting efficiency of LED product packaging, it is necessary to increase the value of n2, that is, to increase the refractive index of the packaging material, in order to increase the critical angle of the product and thus improve the packaging luminous efficiency of the product. At the same time, the encapsulation material should have less absorption of light. In order to increase the proportion of emitted light, it is best to have an arched or hemispherical shape for the packaging. This way, when light is emitted from the packaging material into the air, it is almost perpendicular to the interface and no longer undergoes total reflection.

3. Reflection processing
There are two main aspects of reflection treatment: one is the reflection treatment inside the chip, and the other is the reflection of light by the packaging material. Through both internal and external reflection treatment, the proportion of light emitted from inside the chip is increased, the absorption inside the chip is reduced, and the luminous efficiency of power LED products is improved. In terms of packaging, power type LEDs usually assemble power type chips on metal brackets or substrates with reflective cavities. The bracket type reflective cavity is usually plated to improve the reflection effect, while the substrate type reflective cavity is usually polished and may undergo electroplating treatment if conditions permit. However, the above two treatment methods are affected by mold accuracy and process, and the processed reflective cavity has a certain reflection effect, but it is not ideal. At present, in the production of substrate type reflective cavities in China, due to insufficient polishing accuracy or oxidation of metal coatings, the reflection effect is poor. This results in a lot of light being absorbed after reaching the reflection area, which cannot be reflected to the light emitting surface as expected, leading to a low light harvesting efficiency after final packaging.

4. Selection and Coating of Fluorescent Powder
For white power LED, the improvement of luminous efficiency is also related to the selection of fluorescent powder and process treatment. In order to improve the efficiency of fluorescent powder excitation of blue chips, the selection of fluorescent powder should be appropriate, including excitation wavelength, particle size, excitation efficiency, etc., and comprehensive assessment should be conducted to consider various performance factors. Secondly, the coating of fluorescent powder should be uniform, preferably with a uniform thickness of the adhesive layer on each light-emitting surface of the chip, to avoid uneven thickness that may cause local light to be unable to be emitted, and also improve the quality of the light spot.

Overview:
Good heat dissipation design plays a significant role in improving the luminous efficiency of power LED products, and is also a prerequisite for ensuring product lifespan and reliability. A well-designed light output channel, with a focus on the structural design, material selection, and process treatment of reflective cavities, filling adhesives, etc., can effectively improve the light harvesting efficiency of power type LEDs. For power type white LED, the selection of fluorescent powder and process design are also crucial for improving the spot size and luminous efficiency.