Ultra-violet - SpeedyLook encyclopedia

General information on the ultra-violets (characteristic and effects on health)

Nearly 5% of the energy of the Sun is emitted in the form of radiation UV. These rays UV are classified in three categories according to their wavelength: the GRAPE ones, UV-B and UV-C. However, because of the absorption of UV by the Layer of ozone of the atmosphere, 99% of the Lumière UV which reaches the surface of the ground belong to the range of the GRAPE one.

UV cross even in cold weather the atmosphere or cloudy (they have nothing to do with the feeling of heat gotten by the sun, which is due to the Infrarouge S). They are more numerous between 12:00 and 16:00 and with high-altitude (because while crossing a smaller distance in the atmosphere, they less were likely to be intercepted by molecules of Ozone). UV are reflected by the Eau (5% of UV considered), the Sable (20% of UV considered), grass (5% of UV considered) and especially the Neige (85% of UV considered). The hole in the Couche of ozone is potentially dangerous because of the important harmfulness of the ultra-violets. Note: In the majority of Europe, the sun of the midday, most aggressive, is towards 14:00, this is why it is disadvised exposing itself between 12:00 and 16:00, particularly near the water or of the snow which reverberate part of UV or in mountain where the rates of UV are more important.

Beneficial effects on health

Although UV are harmful, in minor amount radiation UV is beneficial and essential to the synthesis of vitamin D. UV are also used to treat several diseases, of which the Rachitisme, the Psoriasis, the Eczéma and the Ictère.

Index UV

Index UV (or Index UV) is a scale of measurement of the intensity of radiation UV of the sun, and risk which it represents for health.

Index UV is declined in 5 categories, corresponding to a level of risk:

1 - 2: Weak: Wearing of sunglasses in the event of sunny days.

3 - 5: Moderated: You cover, wear a hat and sunglasses. Apply a solar shield of average protection especially (index from 15 to 29) if you are outside during more than 30 minutes. Seek the shade in the neighborhoods of midday when the sun is with the zenith.

6 - 7: Raised: Reduce the exposure between 11:00 and 16:00. Apply a solar shield of high protection (index from 30 to 50), wear a hat and sunglasses, and place you in the shade.

8 - 10: Very high: Without protection, the skin will be damaged and can burn. Avoid the exposure to the sun between 11:00 and 16:00. Seek the shade, cover you, wear a hat and sunglasses, and apply a solar shield of very high protection (index + 50).

11+ : Extreme: The not protected skin will be damaged and can burn in a few minutes. Avoid any exposure to the sun, and if it is not possible cover you absolutely, wear a hat and sunglasses, and apply a solar shield of very high protection (index + 50).

Interactions UV-atmosphere

absorption : at the time of their crossing in the atmosphere, part of rays UV is absorbed by the gas molecules (by the oxygen molecules for example). This phenomenon creates energy able to cause the dissociation of the gas molecule in two other molecules for example.
the diffusion : The ultraviolet rays can also be diffused by the gas molecules contained in the atmosphere. Knowing that more one luminous ray has a short wavelength more it is diffused (that explains why we perceive the sky in blue which is the color of the visible light with the shortest wavelength), one concludes from it that rays UV are strongly diffused by the water droplets of the various vapor clouds. But that inevitably does not involve a fall of the luminous intensity: the high clouds practically do not involve a fall of the intensity while the low clouds diffuse most of rays UV upwards.
the reflection : Rays UV are reflected by the ground according to the nature of the ground. One measures this reflection by a fraction which one calls the Albédo ranging between 0 and 1. The reflection is particularly strong on snow (albedo of 0,9).

The difference between UVA, UVB and UVC

These three types of radiations UV are classified according to their biological activity and to be able to them of penetration of the skin. They correspond to three beaches wavelengths. The more radiation UV has a long wavelength, the less it is harmful (it approaches the visible light) but more it has a capacity of cutaneous penetration. When its wavelength decreases, it has more energy, approaches x-rays and thus is more destroying.

The GRAPE ones (400-315 Nm)

The UVA, of which the wavelength is relatively long, represent nearly 95% of the radiation UV which reaches the surface of the ground. They can penetrate in the deep layers of the skin.

They are responsible for the effect of immediate Bronzage. Moreover, they also support the ageing of the skin and the appearance of wrinkles, by disturbing the balance of the protein syntheses (in particular the degradation of the Collagène) and in the cells they are at the origin of the free radical production of , very detrimental for those. For a long time, it was thought that the UVA could not be at the origin of durable lesions. Recent studies strongly leave think that they could also support the development of the cutaneous Cancers (they affect DNA cell).

On the other hand, they can be beneficial for certain types of pathologies of the skin such as the Psoriasis or the synthesis of Vitamine D.

UV-B (315-280 Nm)

The UVB, average wavelength, have an important biological activity, but do not penetrate beyond the surface layers of the skin, they are relatively absorbed by the cornea layer of the skin (Mélanine). Part of the solar UVB are filtered by the atmosphere.

They are responsible for bronzing and the burns with delayed-action. They are able to produce very strong quantities of free radicals oxygenated in the cells of the skin, short-term persons in charge of the sunstrokes and the Inflammation. In addition to these short-term effects, they support the ageing of the skin (by damaging fibers of Collagène) and the appearance of cutaneous Cancers. Strong intensities of UV-B are dangerous for the eyes and can cause the “flash of the welder” or Photokératite.

UV-C (280-10 Nm)

The UVC, short wavelength, are UV most harmful, but they are completely filtered by the atmosphere and do not reach the surface of the ground.

However, of lamps UV-C are used in laboratory of biology for the germ-destroying effects, in order to sterilize parts or apparatuses (Hotte with laminar flow, for example).

The spectral band of the UV-C consists of three sub-bands:

UV-C from 280 to 200 Nm.
V-UV from 200 to 100 Nm, i.e. UV exploited in the vacuum only.
X-UV from 100 to 10 Nm, transitions electromagnetic between UV and x-rays.

Protection

To defend oneself against light UV, the body, according to the standard of skin, reacts to the exposures by releasing the brown pigment of Mélanine. This Pigment absorbs UV, which makes it possible to block their penetration and to prevent damage with the deeper and more vulnerable layers of the skin. Antioxydant S (vitamins E and C, β-carotene…) can neutralize the free radical formed by UV.

Clothing and sunglasses stop part of UV. There exist lotions which contain ultraviolet filters blocking UV partly, nevertheless, the majority of the dermatologists recommend not to take a prolonged sun bath.

Astronomy

In Astronomy, the very hot objects emit preferentially light UV (Loi of Wien). However, the same layer of ozone which protects us from UV intense coming from the Sun causes difficulties with the astronomers observing starting from the ground. This is why the majority of observations UV are made starting from space.

Use

The fluorescent lamps produce light UV in their tube containing a Gaz with low Pression ; a fluorescent coating on the interior of the tubes absorbs UV which are then re-emitted in the form of visible light.

The halogenous lamps also produce UV and do not have to be used without their glass of protection.

Lamps UV are also used to analyze Minerai S or gem S or to identify any sort of thing, for example banknotes. Objects can appear similar under the light visible and different under light UV. Fluorescent colors UV are employed in many applications (for example in Biochimie or in certain special effects).

Lamps UV wavelength 253,7 Nm are used for to sterilize working areas and tools used in laboratories of biology and medical equipment. Since the micro-organisms can be protected from light UV by small cracks present in the support, these lamps are used only as supplement with other techniques of sterilization.

Light UV is employed for the Photolithographie with very high-resolution, as that is required for the manufacture of the Semi-conducteur S.

UV are also used for the drying of the Encre S and the hardening of some Colle S.

It is recommended to employ protections for the eyes when one works with light UV, particularly for UV short wavelength. Ordinary sunglasses can offer a certain protection, but they are often insufficient.

The Vision of the insects, such that of the Bee S, extends in the spectrum from the close ultra-violet, and the flowers often have visible marks by such pollinating.

Rays UV are also used for the control of banknote authenticity . But attention should be paid: there are already many falsifications in circulation which are also equipped with the fluorescent characteristics. This is why, the detection of counterfeit bills becomes increasingly difficult.

Spectral bands of radiations UV

Radiations UV are electromagnetic waves located between the visible light and x-rays. This category of radiation marks the beginning of the ionizing zone of the electromagnetic spectrum which extends him from 0 Hz to 300 THz million. Here the classification of the UV which is currently most universally allowed:

750,000 to 788,927 THz: end of the visible spectrum of purple and beginning of the transition towards the GRAPE ones.
788,927 to 749,481 THz: spectral transition towards the GRAPE ones.
749,481 to 951,722 THz: GRAPE.
951,722 to 1 070,687 THz: UV-B.
1 070,687 to 29 979,245 THz: UV-C (spectral band made up of 3 sub-bands).

3 spectral sub-bands of the UV-C:

1 070,687 to 1 498,962 THz: UV-C.
1 498,962 to 2 997,924 THz: V-UV.
2 997,924 to 29 979,245 THz: X-UV, i.e. spectral transitions towards x-rays.

Bonds

Internal bonds

black Light
Life and radiation
Information on the detection of counterfeit bills

External bonds

To know index UV in France the Solar Safety
the ultraviolet radiation the World Health Organization
Tpe on the harmful effects of the ultra-violets
Evaluation of the risks associated with the solar benches and the exposure to UV a summary by GreenFacts with the report/ratio with the SCCP with the European commission

Simple: Ultra-violet Zh-min-nan: Chí-goā-soàⁿ

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