Speaking of infrared and laser, you may have heard of them quite a bit. Infrared and laser are not only used in high-end technology products but also in many products we use daily in our lives. For instance, most of the smartphones we use every day have infrared functions. In addition, many household products utilize these two technologies.

Infrared generally refers to infrared light. Infrared (IR) is an electromagnetic wave with a frequency between microwaves and visible light. It is a general term for radiation with a frequency of 0.3THz to 400THz in the electromagnetic spectrum, corresponding to a wavelength of 1mm to 750nm in a vacuum.

Light emitted by atoms through stimulated radiation is called “laser”: after electrons in an atom absorb energy, they transition from a low energy level to a high energy level, and when they fall back from the high energy level to the low energy level, the released energy is emitted in the form of photons. In a beam of photons that is induced (stimulated), the optical characteristics of the photons are highly consistent. Therefore, compared with ordinary light sources, lasers have better monochromaticity, directionality, and higher brightness.

So, what is the difference between an infrared sensor and a laser sensor?

First of all, the difference lies in the source. Because the technologies used are different, the costs and application fields also vary.

Take infrared PM2.5 sensors and laser PM2.5 sensors, for example. Generally speaking, if high precision is required, laser is better; if low cost is required, infrared is relatively lower.

Specifically, there are the following points:

1. The structure and circuit of the infrared PM2.5 sensor are relatively simple. Its light source is an infrared LED. The airflow in and out mainly relies on resistance heating to obtain thermal airflow. When particles pass through, a high level is output. The output signal is only in PWM format.

2. The structure and circuit of the laser PM2.5 sensor are relatively complex. Its light source is a laser diode. The sampled air is pushed by a fan or blower through a complex designed air duct for detection. When fine particulate matter in the air enters the area where the laser beam is located, it causes the laser to scatter; the scattered light radiates 360° in space. We place a photodetector at an appropriate position so that it only receives the scattered light. Then, through the photoelectric effect of the photodetector, a current signal is generated. After circuit amplification and processing, the concentration value of fine particulate matter can be obtained. The output signal is generally a serial port output.

3. Price and Cost: Sensors based on infrared principles have been maturely applied in the industry for many years, with a market price of around ten to several dozen yuan. In contrast, the price of a laser sensor ranges from dozens to hundreds. The cost gap between the two is mainly because the material cost of the latter includes a laser generator and a fan, requires a complex circuit structure, and has a higher technical threshold.

4. Measurement Accuracy: Infrared dust sensors can only detect particles larger than 1 micron, and the measurement accuracy is insufficient. Because the particle signal scattered by infrared LED light is weak, it only responds to large particles greater than 1 micron. Furthermore, it only uses a heating resistor to drive the sampling airflow, resulting in fewer samples, and data calculation is entirely left to the host computer. On the other hand, laser sensors can detect particles as small as 0.3 microns. Because they come with a high-performance CPU and use fans or blowers to collect large amounts of data, analyzed through professional particle counting algorithms, they have advantages over infrared dust sensors in three aspects: sampling count, data source, and algorithm.

5. Application Occasions: Due to insufficient accuracy, infrared sensors are mainly used for industrial and mining dust, where the detection objects are large-diameter, high-concentration dust, and the detection level is mg/m3, making accurate measurement impossible. Laser sensors are mainly applied in the PM2.5 detection field to quantify PM2.5 quality with precision. They can be embedded in smart home air detectors, air purifiers, air quality concentration detection systems, and fresh air systems. In addition, laser sensors are also used in IoT data collection, environmental quality detection, and other fields.

6. Development Trends: Before laser sensors entered the civilian field, infrared sensors were widely used in air purifiers. However, with the development of the air purification industry, the cost of laser sensors is gradually decreasing, and end customers requirements for precise air quality measurement are getting higher. Using laser sensors to precisely quantify PM2.5 quality has become a recognized trend in the industry. Some air purifiers have already adopted laser sensors.

7. Both infrared sensors and laser sensors have their own advantages. Therefore, there is no definitive statement on which PM2.5 detector is better. It depends on the customer requirements (such as cost requirements, accuracy, signal output, application location, and the relevant particles to be tested) to choose the detector that suits them best.

Of course, the above content is not exhaustive. If needed, you can refer to more detailed materials for further learning and understanding.