According to the classification of the laser's danger to the human body, observing the MPE (maximum possible effect) of the eye in the light tree as a benchmark can be divided into one to four levels. Laser product manufacturers should affix Class II, III and IV warning labels to the corresponding laser products. Class I: Low output laser (power is less than 0.4mW), no matter what conditions are to the eyes and skin, will not exceed the MPE value, even after focusing through the optical system will not exceed the MPE value. It can guarantee the safety of the design without special management. Typical applications include laser pointers, CD players, CD-ROM equipment, geological exploration equipment and laboratory analytical instruments, and short-distance communication transmission. (Used when the light source is exposed) Class II: Low-output visible laser (power 0.4mW-1mW), the response time of people closing their eyes is 0.25 seconds, and the exposure calculated with this period of time cannot exceed the MPE value. Usually the laser below 1mW will cause dizziness and unthinkability. It should be protected with closed eyes. It cannot be said to be completely safe. Do not observe directly in the beam. Do not directly illuminate the eyes of others with Class II lasers. II laser. Typical applications are classroom demonstrations, laser pointers, aiming equipment and rangefinders. Class III: Medium output laser. If the light beam directly hits the eyes, it will cause injury. For some safety reasons, it is further divided into IIIA and IIIB. Class IIIA is a continuous laser with visible light. The output is a laser beam of 1-5mW. The energy density of the beam should not exceed 25W / m-m. Avoid using a long-range equipment to observe the IIIA laser, which may increase the risk. The typical application of IIIA has many similarities with Class II, such as laser pointer, laser scanner, etc. III B continuous laser with 5-500mW, it is dangerous to observe directly in the beam. But the minimum irradiation distance is 13cm, and the maximum irradiation time is less than ten seconds for safety. Typical applications of IIIB lasers are spectrometry and entertainment light shows. ClassIV: High-output continuous laser (more than 500mW), higher than the third level, there is a danger of fire, diffusion and reflection are also dangerous. Typical applications are surgery, research, cutting, welding and micromachining. Level 1 is mainly used in laser pointers, CD players, CD-ROM equipment, geological exploration equipment and laboratory analysis instruments. (Used when the light source is exposed) Because the power is less than 0.4mW. So it is not harmful to the eyes. However, because the distance he illuminates does not exceed 1 meter, it is impossible to apply it to the temperature measurement of optical fibers. For some manufacturers, it is impossible to achieve a level 1 rating. In other words, there are other laser grades in his mainframe that are grade 1, but it is definitely not a light source for temperature measurement.