Everyone should be familiar with the UV disinfection lamp. The most common is the public places such as hospitals, restaurants and even school classrooms. Generally, after work personnel leave, they turn on the disinfection. Of course, they are often told that they cannot turn on the disinfection when they are present! But we use it for home use. As for its principle, we are all a bit confused. Why can it be sterilized? Why can't it be opened in the presence of personnel? Isn't it necessary to disinfect when there are many people?



Who discovered ultraviolet?

You first think of Newton, because Newton was the first one to use the prism to decompose the sunlight. In 1666, Newton went to his hometown in the countryside to avoid the plague, and made many amazing discoveries in that dark house, even including the later law of gravitation, so 1666 was the first miracle year for you!



Newton uses prism to decompose sunlight



Newton decomposes sunlight into red, orange, yellow, green, blue, indigo and purple. In fact, the refractive index of different wavelengths of light on the same medium interface is different, but Newton has neither found infrared nor ultraviolet light. Even so, Newton's contribution to optics is still great! The infrared ray was discovered by Herschel in 1800, while the ultraviolet ray was discovered by Ritter, a German scientist, in 1801 when he soaked the paper in silver chloride solution and still had strong light sensitivity outside the violet light!



In 1860's, Maxwell deduced that the speed of electromagnetic wave is equal to that of light accurately measured by Foucault (within the allowable error). Therefore, Maxwell thought that light is only one kind of electromagnetic wave, but in fact, as judged by Maxwell, the visible light we see is only a very short and narrow section of electromagnetic spectrum, even including infrared and ultraviolet bands , still pitifully narrow!



It is generally believed that the wavelength less than 370nm is UV, which is beyond our naked eye's perception, but it does not mean that other animals cannot see it. For example, bees cannot see the visible light whose wavelength is greater than yellow light, but they can see UV, so the world that bees see is different from ours! In addition, our common SLR camera lens also has a uvmirror in front of it, which is used to filter the ultraviolet rays, because we don't need it to interfere with our visible light shooting!



UV mirror





However, it must also be mentioned here, because the sensitivity range of CCD is much wider than that of the naked eye. There is an infrared filter covering the CCD at the bottom of the lens, which filters infrared light. Many people who play with astronomy will dismantle it to increase the sensitivity of the whole CCD, but they must be careful when dismantling it, because the whole CCD will be destroyed by carelessness. Do not use astronomy to change the camera towards summer Day wearing fresh beauty shooting Oh, the florist did not remind you ha!



What is the principle of disinfection?

As for the disinfection principle of ultraviolet, we have to trace back to Comrade Planck who has solved the whole band of blackbody radiation. In 1901, he published a patchwork blackbody radiation formula. Although he didn't know how to get it, this formula solved the radiation calculation of the whole band! Prank was able to introduce the concept of quantum, that is:



E=HV

Energy is equal to Planck constant multiplied by frequency. The higher the frequency is, the greater the energy is. It is consistent with the situation found in the photoelectric experiment, and low-frequency light may not produce electrons. Of course, whether this electron or not has nothing to do with the disinfection we discussed today. It's out of question!

In fact, you can also calculate according to Planck's quantum energy formula. As shown above, if the energy is greater than the bond binding energy, the compound will be photolysis due to the chemical bond breaking, so the aging of various materials caused by ultraviolet is the reason. Because of its strong photon energy, it will break through the vast majority of polymer materials The chemical bond, so plastic products in the sun for a long time will become very brittle, because the fracture of the chemical bond of polymer materials, just like sand!



Schematic diagram of up slope response and down slope response of photodegradation





For example, the wave length of our common UV disinfection lamp is 200-275nm, and the main disinfection radiation band is 250-270nm. This band is good for disinfection of various bacteria. Like photolysis of various polymer materials, the UV energy is higher than the key organic chemical bond binding energy, and the molecular structure of virus DNA material (deoxyribonucleic acid) or RNA (ribonucleic acid) , kill virus or can't split again!





Of course, there are a lot of ultraviolet light waves in the sun, so you should also pay attention to sun protection when working in the sun. If you are not careful to be exposed to the sun, molting is inevitable, but there is an advantage that the first time you are exposed to the sun, it will molt. After peeling, it will be whiter than before. If you are not afraid, you can try it. When the florist rode outdoors in the first few times every year, almost That's all! And then exposed to the sun. Generally speaking, it doesn't peel, just tanned.



Why can't people open it when they're there?

In fact, we should all know that there is no difference between ultraviolet light and sound organisms. That is to say, whether it's human beings, bacteria or viruses, they disinfect you. But human beings are relatively large. Ultraviolet light can only hurt your skin at most. The effect is the same as that of exposure to the sun. Long term exposure to ultraviolet light may cause skin cancer, such as redness, molting, or even skin cancer One effect is the eyes, which can cause conjunctivitis, keratitis, and even cataracts!







So do not turn on the UV disinfection lamp when someone is present!