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UV lamp in the room
Several years ago, when I first turned on a black light lamp in a dark laboratory, I had a feeling of unreality and even fantasy of the environment. Most of the items remained dark - they only slightly reflected the faint violet light of the lamp.
But some objects, inconspicuous in daylight, flashed brightly different colors... Most of all was blue. White wires and a colorless PVC tube, PET bottles and a plastic bucket shone in blue. The paper has become bright white with a bluish tint, the orange plastic has become even brighter. Colored stickers that were used as labels were shining. A white robe, a shirt and some parts of a sweater were glowing.
Recently I tried to experiment with a UV lamp at home (for lack of a laboratory). The impressions were completely different. If the walls in the laboratory were covered tiles and whitewashed, the walls and ceiling of the houses were covered with wallpaper.
Some of the wallpaper was made of paper - the paper glowed in UV light, but stains of glue, paint and other contaminants did not. As a result, the room looked unaesthetic: pollution, hardly noticeable in daylight and electric light, came to the fore - dark spots on a glowing background. Dark brown furniture in ultraviolet light seemed light brown, ugly.
The oil paint in the bathroom looked frankly scary, but in the bath itself I noticed bright blue spots- they shone almost like a phosphor. It turned out that these are frozen pieces water-based paint from which I washed the bucket. The paint looked white, but the bright glow in UV indicated that the paint was actually yellow, White color it is given by a horse dose of optical brighteners.
An unpleasant surprise was that the cat marks glowed green in ultraviolet rays: it became clear that many of the surrounding objects would have to be thoroughly washed.
There was no desire to photograph the surroundings, so I started experimenting. Most of the experiments were carried out in dark room, some - under electric light.
In past experiments, the porcelain mortar I photographed under UV light in the lab looked dark purple (i.e. it just reflected the dim purple light from the lamp).
It turned out that the white porcelain plates behaved similarly, but there was also a significant difference. Visually, the plates look almost clean, but it is worth turning on the black light lamp and the remains of dirt become noticeable on the plate and detergent: Porcelain is not glowing, and dirt and / or detergent is green.
The inner side of the hand looked light in ultraviolet rays, but the outer side looked dark (like a black man's) - only the nails shone. In the photographs, the difference is not very clear, tk. in the case of the outside of the hand, the exposure was significantly longer.
The monitor screen (with a ray tube) glowed green in ultraviolet rays, and not very intensely. This is not surprising, since the phosphors applied to the kinescope screen are designed to glow under the action of an electron beam, and not soft ultraviolet rays.
The toy mouse, made of cloth, looked much more beautiful in ultraviolet light - some areas glowed brightly. The glow was noticeable even under electric light.
The colorless PET bottle glowed blue in ultraviolet light - so bright that it was clearly visible even when the electric light was on.
But the most brightly shone was the colorless PVC tube - it literally burned blue, like a fluorescent lamp. There is no doubt about the presence of optical brighteners.
Most people when asked "What is luminescence?" remember fluorescent discharge lamps. Indeed, this is one of the most famous applications of a bright (literally) physical phenomenon, namely photoluminescence (excitation by light). Glass tubes contain mercury vapors, excited by an electric discharge and emitting in the ultraviolet region. The coating applied to the tube walls - a phosphor - converts ultraviolet light into radiation visible to the human eye. Depending on the type of phosphor, the glow color can be different - this makes it possible to produce lamps not only "cold" and "warm" light, but also different colors- red, blue, etc. that appeared in recent times energy-saving lamps, which surpass incandescent lamps in the visible light range, are the same fluorescent lamps, only greatly reduced due to the miniaturization of electronics. Another type of luminescence is cathodoluminescence. It is she who underlies the cathode-ray tubes: the phosphor covering the screen glows under the action of an electron beam. X-ray luminescence, for example, is used in fluorography - a screen covered with a phosphor glows when exposed to X-rays.
According to the definition given in Physical encyclopedia, luminescence radiation, which is an excess over the thermal radiation of the body and continues for a time significantly exceeding the period of light oscillations. The first part of the definition separates luminescence from thermal equilibrium radiation and shows that this concept is applicable only to a set of atoms (molecules) in a state close to equilibrium. With a strong deviation from the equilibrium state, it makes no sense to talk about thermal radiation or luminescence. In the visible region of the spectrum, thermal radiation becomes noticeable only at a body temperature of thousands of degrees, while it can luminesce in this region at any temperature; therefore, luminescence is often called cold glow. The second part of the definition (a sign of duration) was introduced by S.I. Vavilov to separate the luminescence from different types scattering, reflection, parametric transformation of light, bremsstrahlung and Cherenkov-Vavilov radiation. In contrast to light scattering, during luminescence, intermediate processes occur between absorption and emission, the duration of which is longer than the period of the light wave. As a result, during luminescence, the correlation between the oscillation phases of the absorbed and emitted light is lost.
Fast and slow
After termination of the excitation, the luminescence decays. If this happens quickly, then the process is attributed to fluorescence (from the name of the mineral fluorite, in which this phenomenon was discovered), and if the glow continues long time- then to phosphorescence. Fluorescence under the influence of light (visible and UV) can often be observed in everyday life - the dyes of markers, road sign coatings and workwear fabrics glow. It is fluorescence that is responsible for the fact that freshly washed White shirt seems bright sunlight"Whiter than white". And this effect is not psychological. Just washing powders contain special substances, optical brighteners, which, under the influence of ultraviolet radiation, emit visible light (usually in the blue-violet region). This also explains the fact that white clothing glows under the influence of UV lamps in discos. Slowly decaying luminescence (phosphorescence) is also very common in everyday life - remember the dials of watches and hands of other devices (as well as the screens of old oscilloscopes).
Other
In addition to the aforementioned varieties, there is radioluminescence - under the action of penetrating radiation (used in scintillation counters), chemiluminescence under the action of chemical reactions(including bioluminescence), candoluminescence (under mechanical stress), luminescence (when crystals dissolve), electroluminescence (under the action electric field), etc. Some of them are quite familiar to readers. For example, the glow of white phosphorus is the result of chemiluminescence: being oxidized under the influence of atmospheric oxygen, phosphorus vapors glow. Oxidation also explains the glow of plastic "flashlights" - chemical light sources, only they do not use phosphorus and oxygen, but an organic dye and hydrogen peroxide.
There are no secret inscriptions
Luminescence under the influence of ultraviolet radiation is actively used to verify the authenticity of various documents, forms and banknotes. Now almost any cashier has a machine with a UV lamp at hand for checking banknotes. This method has been used since the beginning of the 20th century; Robert Wood, the famous American physicist, experimented with it at the end of the First World War. This is how Wood himself describes it in the book by his biographer William Seabrook “Robert Wood. The modern magician of the physical laboratory ":
... They [the Bureau of the Chief Censor of the British Navy] proudly told me that they had invented paper on which it was impossible to make an "invisible" secret record. It was sold in all post offices, and the letters written on it could not be subjected to any tests. This paper became very popular as the letters were not delayed by the censorship. It was regular note paper printed with frequent parallel lines, pink, green, and blue. Red paint was diluted in water, green in alcohol, and blue in gasoline. The paper looked gray to the eye. Since almost any liquid in which invisible ink is dissolved belongs to one of these three classes, one of the colored lines will dissolve in the colorless liquid flowing from the pen, and traces of the inscription will appear. I remembered that Chinese whitewash turns out to be black as coal in photographs taken in ultraviolet rays, and I said: “Suppose I would write on it with a thin stick with Chinese whitewash - then none of the lines will dissolve, and yet the inscription can be will read it if you take a photo of the paper. "
Marks applied invisible ink, glowing in ultraviolet light, are very often used to determine the authenticity of various documents. And the paper itself, as a rule, contains fibers that glow in ultraviolet light.
“Oh no,” they replied, “you can write on it even with a toothpick or glass stick without any paint. The colored lines are made slightly soft or tacky so that they smudge into dark gray letters. Here's a glass rod - try it yourself! " (...)
I said, “Okay. I'll try, though. Bring me a rubber stamp and some Vaseline. " They brought me a large, sleek clean stamp of military censorship. I rubbed it with Vaseline, then wiped it off with a handkerchief until it stopped leaving marks on the paper. Then I pressed it tightly against the "spy-resistant" paper, preventing it from sliding to the side.
"Can you find an inscription here?" I asked.
They tested the paper in reflected and polarized light and said, "There is nothing here."
“Then let's light it up ultraviolet rays". We took her to the booth and put her in front of my black window. On the paper, in bright blue letters, as if a stamp had been applied to it, smeared with ink, the words shone: "There are no secret inscriptions."
Searching for traces of blood on different surfaces, as well as the instruments of crime - this is one of the main tasks faced by employees of forensic centers and departments. At the same time, traces of blood can not always be identified visually. They can be washed out or have microscopic dimensions, which requires the use of specific methods for their search, in particular, ultraviolet light.
The second area of application of ultraviolet lights is hunting for wounded animals on the trail of blood by hunters. Because on vegetation or soil at night it is very difficult to replace it.
How blood glows in ultraviolet light
Answering the question of whether blood glows in ultraviolet light, it should immediately be noted that this biological fluid does not fluoresce under the influence of UV rays. Blood completely absorbs the entire spectrum of ultraviolet radiation, acquiring an absolutely black color. It is for this reason that in various specialized forums one can find negative reviews about lanterns (people expect it to start glowing) designed to search for blood. BUT the black color of blood is also a result. Because all other surfaces (grass, vegetation, earth, leaves) reflect ultraviolet light. Those. BLACK traces of blood will be clearly visible on the gray-blue-white forest surface. Therefore, you can answer YES, a UV flashlight can help you find the wounded animal. But not in the way that many expect after watching movies. By the way, we will explain this below.
But how and why, in this case, ultraviolet is used to identify blood in criminology around the world?
In fact, the identification of blood is carried out using a special method, the essence of which is the processing of the alleged places of the presence of its traces with a special composition - luminol. This organic compound is capable of reacting with hemoglobin, which results in a blue fluorescence. That is why blood treated with such a composition glows in ultraviolet light. It should be noted that this method provides the ability to detect even the smallest in size and washed out with cleaning agents traces of blood, since it is almost impossible to completely erase them.
Another feature of the search for blood with ultraviolet light is the short-term irradiation of its traces. The fact is that UV irradiation destroys the DNA in the blood, which makes it impossible to further study it. That is why, when a positive reaction is received, the effect of UV light on the blood is suspended, and its samples are taken for further laboratory studies. 
The catalog of our online store contains a wide selection of professional forensic and hunting UV lights for detecting traces of blood. Each offered model is developed on the basis of original high quality components and meets all modern standards. Wholesale supplies of flashlights to forensic centers and specialized laboratories are possible.
Ultraviolet is part of the spectrum electromagnetic radiation, which is beyond the boundaries of our perception. Simply put - not visible radiation... But not really. The light we see is limited to wavelengths between 380 nm and 780 nm (nanometers). Ultraviolet wavelength or ultraviolet radiation lies in the range from 10 nm to 400 nm. It turns out that we can still see ultraviolet light - but only a small part of it, located in a small interval between 380 and 400 nm.
Everything. Dry facts are over, interesting facts begin. The fact is that this barely visible radiation actually plays a huge role not only in the biosphere (we will certainly tell you about this separately), but also in lighting. Simply put, ultraviolet light helps us see.
Ultraviolet and lighting
The main application of ultraviolet light is found in lamps. Electrical discharges cause the gas inside a fluorescent lamp (or compact fluorescent lamp) to glow in the ultraviolet range. In order to obtain visible light, a special coating of a material is applied to the walls of the lamp, which will fluoresce - that is, glow in the visible range - under the influence of ultraviolet radiation. This material is called a phosphor, and manufacturers are constantly working to improve its composition in order to improve the quality of the visible light received. That is why today we have a good selection of fluorescent lamps, which not only outperform conventional incandescent lamps in energy efficiency, but also produce almost full spectrum light, which is quite pleasing to the eye.
What other uses for ultraviolet radiation can be?
Exists whole line materials that can glow in ultraviolet light. This ability is called fluorescence - it is possessed by many organic substances. In addition to it, there is also the so-called phosphorescence - its difference is that the substance emits light with a lower intensity, but continues to glow for some time (often quite long - up to several hours) after the cessation of exposure to ultraviolet radiation. These properties are actively used in the manufacture of various "glow in the dark" items and jewelry.
An infectious disease caused by the fungus dermatophyte is called shingles. Microscopic organisms live on the skin, specifically in the hair follicles. The fungus responsible for ringworm is found in the soil, so cats and large cattle most often become infected with it. Disputes persist environment up to two years even for garden tools, shoes, carpets.
Children who try everything with their hands, and sometimes with a tooth, are exposed to infection due to weak immune system... The disease is transmitted to humans through pets or from an infected environment. Epidermophytosis of the feet and groin is most often spread in public locker rooms and swimming pools.
Lichen appears as a small lesion with scaly skin in the center. Gradually, it grows larger, causing hair loss. The lesions are not always circular and hair does not always fall out completely. Baldness can be accompanied by redness and inflammation. Hair can grow even while there is an infection on the body, so the disappearance of bald spots does not indicate a cure.
More accurate methods are required for diagnosis. Dermatologists often study pathological changes in the skin under a Wood's lamp in order to choose a further direction for examinations or to confirm their own guesses.
Fluorescent lamp
A Wood's lamp is a diagnostic tool in which the affected skin, under the influence of black light, causes a certain glow. Black light is waves invisible to the naked eye in ultraviolet spectrum that glow purple in the dark.
The traditional Wood lamp was equipped with a mercury coating for emitting a wavelength of 320-450 nm and was invented in 1903 by physicist Robert Wood. Modern black light sources are developed from fluorescent, mercury, light emitting lamps, diodes or incandescent lamps. It is the dark blue coating on the pipe that filters out most of the visible light waves.
Luminescent diagnostics
To diagnose skin problems under a Wood lamp, several steps must be followed:
- Wash the skin, remove makeup, moisturizers and other cosmetics, as it can cause a false positive result.
- Turn on the lamp to warm up for a minute.
- Turn off the lights in the office and curtain the windows to create darkness.
- When vision adapts to darkness, direct the light from the lamp to the skin at a distance of 10-30 cm.
The fluorescent color allows the detection of pigmented or depigmented spots.
Normal healthy skin glows lightly in blue, thickened areas appear white and oily areas appear yellow, dehydrated skin turns purple.
To distinguish lichen infectious from other skin lesions, a Wood lamp is used. The test result is positive if the pigmentation becomes more pronounced against the background of the test.
Glow features
Fluorescent black becomes visible when collagen or porphyrins absorb it and emit it in the visible spectrum. Thread, hair, drug and soap residues on the skin can also fluoresce.
What color lichen glows under ultraviolet light for various skin pathologies:
- Increased pigmentation (melasma, post-inflammatory pigmentation). The lesions have clear boundaries under the light of the lamp due to the increase in the level of melanin in the cells.
- Loss of pigmentation (vitiligo, tuberous sclerosis, hypomelanosis) should be detected in fair-skinned individuals. The lesions will glow bright blue (sometimes yellowish green) due to the accumulation of biopterins. Areas with decreased blood flow do not change under light.
- Pityriasis versicolor is a slightly scaly, persistent rash on the front of the chest and back caused by fungi. Under the light, the lamps glow orange or yellow. Tinea versicolor disrupts pigmentation under the action of a fungus, and its spots become more pronounced under ultraviolet light.
- In folliculitis caused by the yeast malassezia, the hair follicles give off a bluish-white light.
- The glow with ringworm depends on the type of fungal infection: with microsporia it is blue-green (M canis, M. audouinii, M distortum), and with trichophytosis it is pale blue. Fungal infections caused by other organisms do not fluoresce
- Erythrasma caused by corynebacteria is accompanied by a pigmented rash in the folds of the skin that turn coral pink.
- Lichen planus is diagnosed by the appearance of whitish-yellow spots.
- Pink and shingles are examined with a Wood lamp for differential diagnosis only. Herpes virus is confirmed by DNA detection by polymerase chain reaction in the liquid that is taken from the blisters of the rash. Inflammatory processes are highlighted in white, which can also indicate an immune response to viruses or bacteria.
Wood's lamp directs diagnostics in the right direction. The most contagious type of fungus that causes lichen is microsporum. To confirm infection, bacterial culture is carried out under laboratory conditions, requiring at least 10-14 days. Therefore, a fluorescent lamp with a Wood filter acts as an express diagnostic method.
Fresh ringworm lesions on the hair may not be visible with a lamp because signs of damage are minor. The dermatologist recommends removing hair from the suspected area of infection in order to examine the roots. Even after the death of the fungus, the hair continues to glow.
Diagnostic rules
Wood's lamp helps to identify lesions of lichen on smooth skin, hair, nails, eyebrows. The dermatologist uses a protective mask or goggles to protect the vision from the direct radiation of the lamp. The patient will be asked to close their eyes. The procedure lasts on average 1-2 minutes and does not require additional actions on the part of the patient. Sometimes a microscope is used to examine the condition of the skin in detail.
It must be remembered that a luminescent examination only complements the basic diagnosis, allows one to suspect a certain disease.
So a glowing white focus means inflammation, vitiligo, candidiasis, systemic lupus erythematosus. Therefore, differential diagnosis requires taking a scraping and analyzing the material under a microscope.
The experienced eye of a dermatologist is capable of identifying the shade of a particular pathology. At home, Wood's lamp can refute or confirm the need to see a doctor when a rash appears on the body or head.
UV treatment
If fungal infections can be diagnosed ultraviolet lamps, then other skin lesions lend themselves to physiotherapy of the same name. The herpes virus, which causes shingles, is sensitive to ultraviolet light. Therefore, dermatologists use physiotherapy procedures that contribute to the gradual disappearance of stains. Pink lichen can be healed on its own, even in a tanning bed, if it does not respond to therapy and is prone to relapse.