Exposing things to the sun is the ancient clean wisdom of human society. Although people didn't understand the principle, they had started to use sunlight to dry and clean things thousands of years ago. Now, research by scientists tells us that sunlight contains ultraviolet rays, which make the sunlight have some bactericidal effects.

So, can sunlight kill bacteria as quickly and thoroughly as a household UV sterilizer? The answer is no!

Different ultraviolet rays

As known, UV can kill bacteria and viruses. It’s just that many people don’t know that what people call UV is a collection of ultraviolet rays with different wavelengths, including UVA, UVB, UVC, etc. Ultraviolet light with different wavelengths has different characteristics. Among them, the radiant energy contained in UVC is more easily absorbed by biological cells, the atmosphere, and other substances than UVA and UVB.

The original sunlight has contained all kinds of ultraviolet rays while it was in the universe, including UVA, UVB, UVC, etc. When sunlight passes through the atmosphere, all UVC, most UVA, and most UVB will be absorbed by the atmosphere. So, while the sunlight reaches the earth's surface, it just contains a small amount of UVA and UVB with less energy.

For sterilization speed, UVC's wavelength and energy are within the absorption peak range of microorganisms, it can kill viruses and bacteria by destroying the DNA structure of microorganisms within 1s. UVA and UVB are outside the absorption peak range of microorganisms. So, their sterilization speed is very slow, will take several hours to achieve a sterilization effect. Therefore, household UV disinfection equipment such as home kitchen UVC LED sanitizer usually uses high-efficiency UVC light sources. They have sufficient energy and generally only take a few minutes to complete the sterilization. And this will take a so long time under sunlight.

Shadows

There is another reason why sunlight is not an ideal choice for sterilization, that is, when we irradiate objects with sunlight, we usually cannot guarantee that the light directly reaches all corners. Ultraviolet rays have very special characteristics. In general, when ultraviolet rays pass through the transmission, refraction, or reflection of conventional objects, most or even all of the energy will be absorbed. Then the light sterilization ability will be lost.

As products specifically designed for sterilization, most UV disinfection equipment usually applies kinds of designs to ensure the ideal effect to their target object. For example, the ATYOU UV baby bottle steriliser, this product points UVC LEDs to the inside of the baby bottle. With that, the UV can directly irradiate into the bottle cavity, ensuring that the inside of the cavity can also be thoroughly cleaned without dead ends.

However, although sunlight cannot be as targeted and efficient as UV light air purifier and other products, it is still a good cleaning assistant in life. Open the windows frequently and let the sunshine in to the house, keep the room dry and breathable, which will make the room less susceptible to bacterial invasion.