不同波段紫外線對(duì)人體影響

紫外線探傷燈，俗稱紫外線燈，是無(wú)損探傷、脫脂清洗檢查、熒光泄露撿漏……中用于激發(fā)熒光染料/物質(zhì)的光源。隨著人們安全意識(shí)的提高，在購(gòu)買(mǎi)和使用紫外線燈的時(shí)候總會(huì)問(wèn)：使用紫外線燈對(duì)身體會(huì)有什么傷害？使用的過(guò)程中我應(yīng)該怎么去保護(hù)自己？帶著這些問(wèn)題，我們來(lái)看看。

在紫外線燈還是處于高壓汞燈的時(shí)候，在國(guó)外就用和紫外線燈同類種的紫外線燈作為美黑設(shè)備，在專業(yè)人士的指導(dǎo)下，照射皮膚，使皮膚變成古銅色。紫外線的波長(zhǎng)分為長(zhǎng)波（UVA）、中波（UVB）、短波(UVC),不同波段的紫外線對(duì)人體的傷害是不太一樣的：

UVA波段：波長(zhǎng)320～400nm，又稱為長(zhǎng)波黑斑效應(yīng)紫外線。太陽(yáng)光中含有的UVA有超過(guò)98%能穿透臭氧層和云層到達(dá)地球表面，UVA可以直達(dá)肌膚的層，破壞彈性纖維和膠原蛋白纖維，將我們的皮膚曬黑和老化。長(zhǎng)期暴曬，可以導(dǎo)致皮膚產(chǎn)生癌變。

UVB波段：波長(zhǎng)275～320nm，又稱為中波紅斑效應(yīng)紫外線。太陽(yáng)光中含有的UVB大部分被臭氧層所吸收，只有不足2%能到達(dá)地球表面，在夏天和午后會(huì)特別強(qiáng)烈。UVB紫外線對(duì)人體具有紅斑作用，能促進(jìn)體內(nèi)礦物質(zhì)代謝和維生素D的形成，但長(zhǎng)期或過(guò)量照射會(huì)令皮膚曬黑，并引起紅腫脫皮。此類紫外線的極大部分被皮膚表皮所吸收，不能再滲入皮膚內(nèi)部。但由于其階能較高，對(duì)皮膚可產(chǎn)生強(qiáng)烈的光損傷，被照射部位血管擴(kuò)張，皮膚可出現(xiàn)紅腫、水泡等癥狀。長(zhǎng)久照射皮膚會(huì)出現(xiàn)紅斑、炎癥、皮膚老化，嚴(yán)重者可引起皮膚癌。

UVA和UVB對(duì)皮膚的輻射深度示意圖

UVC波段：生物學(xué)稱為短波滅菌紫外線，波長(zhǎng)200～275nm，又稱為短波滅菌紫外線，太陽(yáng)光中含有的UVC完全被臭氧層所吸收。UVC對(duì)人體的傷害很大，短時(shí)間照射即可灼傷皮膚，長(zhǎng)期或高強(qiáng)度照射還會(huì)造成皮膚癌。紫外線燈發(fā)出的就是UVC短波紫外線（臭氧層的減少和皮膚癌的增多有直接關(guān)系）。

紫外線燈（黑光燈）需要的紫外線光為365nm附近的光譜，這段光譜對(duì)熒光物質(zhì)的激勵(lì)效率高。對(duì)于LED冷光源紫外線燈，光輻射95%以上都是在365nm附近的UVA成分，不含有UVB和UVC成分，即紫外線燈對(duì)人體造成的影響就是UVA波段對(duì)人體的傷害“直達(dá)肌膚的層，破壞彈性纖維和膠原蛋白纖維，將我們的皮膚曬黑”，短時(shí)間的照射對(duì)皮膚基本無(wú)傷害，那這個(gè)短時(shí)間怎么去界定？

根據(jù)美國(guó)政府工業(yè)衛(wèi)生學(xué)家會(huì)議（ACGIH）的規(guī)定：工業(yè)探傷紫外線燈歸類為3級(jí)UV危險(xiǎn)源，針對(duì)長(zhǎng)波段紫外UVA，每年人體可以承受的紫外zui大輻射劑量為3333kJ/m2，每八小時(shí)zui大照射量為10kJ/m2。而一般的工業(yè)紫外線燈照度在5000uW/cm2(=50W/m2)左右；按此計(jì)算，人體裸露皮膚被紫外線直接照射的時(shí)間不應(yīng)超過(guò)200秒。因此，做熒光檢測(cè)時(shí)，必須佩帶紫外線防護(hù)手套，避免人體的皮膚被直接照射到。另外紫外線直射眼睛傷害很大，作業(yè)時(shí)應(yīng)佩戴紫外線防護(hù)眼鏡。

What is the Difference between UVA UVB UVC?

 Which is Most Dangerous?

UVA, UVB, UVC- all of these are forms of ultraviolet light rays that are naturally occurring, but they are not created equal. We'll explain the differences between these three forms of radiation, and then discuss how UVC is harnessed in man-made lighting products to inactivate pathogens (kill germs).The sun is responsible for emitting each of the different types of ultraviolet light. UV rays are also found in man-made products, like tanning beds and welding torches. Although UV rays have some benefit, namely encouraging vitamin D production in humans, everyone should practice caution as each form of UV comes with its own risks.

UVC
UVC is the shortest wavelength of the three forms of UV. The shorter the wavelength, the more harmful the UV radiation. However, lucky for us, UVC isn't able to penetrate earth's atmosphere. So while UVC is the most dangerous because it's the shortest wavelength, it's not a risk to the typical person because the sun's natural UVC emissions don't penetrate skin. Remember, they actually do not even penetrate earth's atmosphere naturally at all. UVC is absorbed completely by the ozone layer.

This is not to say that UVC isn't dangerous. Although naturally occurring UVC doesn't permeate earth's atmosphere, inorganic sources of UVC radiation exist and are dangerous when not used properly. So, the people who need to be concerned about UVC radiation are those working with these man-made sources of UVC, like welding torches, mercury lamps, and, you guessed it, germicidal UV-C lighting, which we distribute. More on this after we define UVA and UVB.

UVB
UVB is the second shortest wavelength and the main culprit of sunburn. It's mostly absorbed by the ozone layer but still gets through (about 5% gets through overall). It harms the top layer (epidermis) of your skin in as little as 15 minutes of sun exposure. UVB rays are stronger or weaker depending on the time of day and season. There is a strong link between UVB rays and skin cancer. UVB rays do age skin over time.

UVA：
UVA is the longest wavelength, penetrating the deepest and causing the vast majority (upwards of 95%) of UV radiation getting through earth's atmosphere. This is the form of radiation that causes skin aging, like spots and wrinkles, because it does reach so deeply into skin layers (through to the dermis layer). UVA rays can tan your skin right away, and do appear to be linked to cancer. UVA rays, unlike the others, penetrate glass and clouds, causing harm on overcast days or via your windshield.

Protect Yourself
You should protect yourself from UVA and UVB rays by applying broad spectrum sunscreen, wearing UPF clothing and sunglasses, and blocking UV rays with umbrellas and car shades as needed.

Most Dangerous?
So, which is the most dangerous type of UV radiation? There isn't a good answer to this question, although it's asked frequently. On the one hand, UVC is the most dangerous because it's the highest energy portion on the UV spectrum. However, UVC is completely absorbed by earth's atmosphere so it's really not a risk to most people. It's only a risk to those exposed to artificial sources of UVC (see more below).

If we choose the most dangerous based on exposure, then UVA is the clear forerunner for danger. It accounts for nearly all UV exposure as it's barely blocked by the earth's atmosphere. That said, it's also the shortest wavelength and isn't thought to cause as much long-term damage as UVB from the sun.

Although only a small amount of UVB penetrates earth, we'd consider it the most damaging to your average person (not those working incorrectly with artificial UVC sources) because it comes with the highest skin cancer risk.

Artificial UVC
All forms of UVC radiation are artificial since the sun's UVC doesn't get through earth's atmosphere, as discussed. Some common sources of man-made UVC radiation are:

Older tanning beds
Lasers
Mercury lamps
Welding torches
Germicidal UV-C lighting
Not all artificial forms of UVC are equal in risk/reward. For instance, tanning beds are unnecessary and dangerous and should be avoided. Don't purposefully expose yourself to harmful radiation (note that most modern tanning beds use UVA radiation, which is still dangerous). Welding torches, conversely, are necessary for some jobs, and using the proper protective gear mitigates the risk of your UV exposure. Also, becoming a welder takes lots of training; they're prepared for this risk.

Germicidal UV-C lighting, when used properly, is operated in empty spaces using controls for safety. The reward of having killed up to 99.99% of pathogens from, say, personal protective equipment (PPE), outweighs the nearly non-existent risk of UV exposure.

Moreover, not all artificial UVC sources operate at the same wavelength. While UVC in general encompasses wavelengths of 100-280 nm, it varies from product to product where they are in that range. For example, one lamp that we distribute operates at 254 nm.

In conclusion, if you were to be exposed to artificial forms of UVC radiation, it would be detrimental (we talk about this in more detail here) but as long as equipment is used as directed, the benefits of UV-C technology outweigh the risks in most cases. It's like any technology- will the radiation from an x-ray machine harm you? Yes, but we have controls in place to ensure that the radiation from an x-ray machine can't harm you, and we won't stop using x-ray machines just because of this risk.