The role and precautions of LED light sources in visual systems

The machine vision system mainly consists of three parts: image acquisition, image processing and analysis, and output or display. Image acquisition is the core of machine vision, and the image acquisition system consists of three parts: light source, lens, and camera. Whether the selection and lighting of the light source is reasonable or not can directly affect at least 30% of the imaging quality. So the light source is a very important part of the machine vision system.

1. Illuminate the target and increase the brightness of the target,
2. Highlight measurement features and simplify image processing algorithms;
3. Overcome the interference of ambient light, ensure image stability, and improve image signal-to-noise ratio;
4. Improve the positioning, measurement, and recognition accuracy of the vision system, as well as the system’s operating speed;
5. Reduce the complexity of system design and form the imaging effect that is most beneficial to image processing;

The stability and quality of LED light source lamps are crucial to the heat dissipation of the lamp itself. The heat dissipation of high-brightness LED light source lamps currently on the market often uses natural heat dissipation, and the effect is not ideal. If the LED light source cannot dissipate heat well, its lifespan will also be affected. Therefore, you should pay attention to the following points when using LED light sources:

1. The impact of heat on high-brightness LED light sources

   Heat is concentrated in a chip with a very small size, and the temperature of the chip increases, causing non-uniform distribution of thermal stress, a decrease in the chip's luminous efficiency and phosphor lasing efficiency; when the temperature exceeds a certain value, the device failure rate increases exponentially. Statistics show that for every 2°C increase in component temperature, reliability drops by 10%. When multiple LED light sources are densely arranged to form a white light lighting system, the heat dissipation problem is more serious. Solving the thermal management problem has become the primary condition for the application of high-brightness LED light sources.

2. The relationship between chip size and heat dissipation

   The most direct way to improve the brightness of a power LED light source is to increase the input power. In order to prevent saturation of the active layer, the size of the pn junction must be correspondingly increased; increasing the input power will inevitably increase the junction temperature, thereby reducing the quantum efficiency. The increase in single-tube power depends on the device's ability to dissipate heat from the pn junction. While maintaining the existing chip material, structure, packaging process, unchanged current density on the chip, and equivalent heat dissipation conditions, if the size of the chip is increased alone, the junction temperature will continue to rise.

3. Thermal management is the main issue in the application of high-brightness LED light sources.

   Since the p-type doping of Group III nitrides is limited by the solubility of the Mg acceptor and the high starting energy of the hole, heat is particularly easy to be generated in the p-type region, and this heat must pass through the entire structure to be dissipated on the heat sink; the heat dissipation path of the LED device is mainly thermal conduction and thermal convection; the extremely low thermal conductivity of the Sapphire substrate material causes the thermal resistance of the device to increase, resulting in a serious self-heating effect, which is devastating to the performance and reliability of the device.