Search for traces of blood on various surfaces, as well as the instruments for committing a crime - this is one of the main tasks faced by employees of forensic centers and departments. However, traces of blood cannot always be identified visually. They can be washed out or have microscopic sizes, which requires the use of specific methods for searching for them, in particular ultraviolet light.
The second area of application of ultraviolet flashlights is the search for wounded animals by hunters following the blood trail. Because on vegetation or ground at night it is very difficult to replace.
How blood glows in ultraviolet light
When 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 ultraviolet spectrum, becoming completely black. It is for this reason that on various specialized forums you can find negative reviews about flashlights (people expect it to glow) designed to search for blood. BUT the black color of blood is also a result. Because All other surfaces (grass, vegetation, soil, leaves) reflect ultraviolet light. Those. BLACK traces of blood will be clearly visible on the gray-blue-white surface of the forest. Therefore, you can answer YES, a UV flashlight can help you find a wounded animal. But not in the way many people expect after watching enough films. By the way, we will explain this below.
But how and why, in this case, is ultraviolet used to identify blood in criminology around the world?
In fact, blood identification is performed using a special method, the essence of which is to process the suspected locations of its traces. special composition– luminol. This organic compound is capable of reacting with hemoglobin, which leads to blue fluorescence. That is why blood treated with this composition glows in ultraviolet light. It is worth noting that this method makes it possible to detect even the smallest traces of blood that are washed away with cleaning agents, since it is almost impossible to completely erase them.
Another feature of searching for blood with ultraviolet light is the short-term irradiation of its traces. The fact is that UV irradiation destroys DNA in the blood, which makes it impossible to further study it. That is why, when a positive reaction is obtained, the effect of UV light on the blood is suspended, and its samples are taken for further laboratory tests. 
The catalog of our online store presents a wide selection of professional forensic and hunting UV flashlights 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.
Most people, when asked “What is luminescence?” remember fluorescent gas-discharge lamps. Indeed, this is one of the most famous applications of a bright (literally) physical phenomenon, namely photoluminescence (excitation by light). IN glass tubes there are mercury vapors excited by an electrical discharge and emitting in the ultraviolet region. A coating applied to the walls of the tube - phosphor - converts ultraviolet radiation into radiation visible to the human eye. Depending on the type of phosphor, the color of the glow can be different - this makes it possible to produce lamps not only of “cold” and “warm” light, but also different colors- red, blue, etc. Energy-saving lamps that have appeared recently, superior to incandescent lamps in the field of visible light, are the same fluorescent lamps, only greatly reduced due to the miniaturization of electronics. Another type of luminescence is cathodoluminescence. It is this that underlies cathode ray tubes: the phosphor covering the screen glows under the influence of a beam of electrons. X-ray luminescence, for example, is used in fluorography - a phosphor-coated screen glows under the influence of x-rays.
According to the definition given in the Physical Encyclopedia, luminescence is radiation that is an excess over the thermal radiation of the body and lasts 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) that are in a state close to equilibrium. If there is 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, which is why luminescence is often called cold glow. The second part of the definition (duration characteristic) was introduced by S.I. Vavilov to separate luminescence from various types scattering, reflection, parametric transformation of light, bremsstrahlung and Cherenkov-Vavilov radiation. Unlike 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 phases of oscillations of absorbed and emitted light is lost.
Fast and slow
After the excitation ceases, the luminescence fades. If this happens quickly, then the process is referred to as fluorescence (from the name of the fluorite mineral in which this phenomenon was discovered), and if the glow continues for a 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, the coating of road signs and the fabrics of workwear glow. It is fluorescence that is responsible for the fact that a freshly washed white shirt appears in bright light. sunlight"whiter than white" And this effect is not psychological. It’s just that washing powders contain special substances, optical brighteners, which, when exposed to ultraviolet radiation, emit visible light (usually in the blue-violet region). This explains the fact that white clothes glow under the influence of UV lamps in discos. Slowly decaying luminescence (phosphorescence) is also very common in everyday life - think of watch dials and hands of other devices (as well as the screens of old oscilloscopes).
And others
In addition to the above-mentioned varieties, there are radioluminescence - under the influence of penetrating radiation (used in scintillation counters), chemiluminescence under the influence chemical reactions(including bioluminescence), candoluminescence (under mechanical influences), lyoluminescence (with dissolution of crystals), electroluminescence (under the influence electric field) etc. Some of them are quite familiar to readers. For example, the glow of white phosphorus is the result of chemiluminescence: phosphorus vapors oxidize under the influence of atmospheric oxygen. Oxidation also explains the glow of plastic “flashlights” - chemical light sources, only they do not use phosphorus and oxygen, but 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. Nowadays, almost every cashier has at hand a device with a UV lamp 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 of his biographer William Seabrook “Robert Wood. Modern sorcerer of the physical laboratory":
...They [Office 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 letters written on it could not be subjected to any tests. This paper became very popular because the letters were not delayed by censorship. It was ordinary notepaper, 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 white turns out to be as black as coal in photographs taken in ultraviolet rays, and I said: “Suppose I wrote on it with a thin stick with Chinese white - then none of the lines will dissolve, and yet the inscription can still be written.” will be readable if you photograph the paper.”
Marks made with invisible ink that glow under ultraviolet light are 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 even write on it with a toothpick or a glass rod without any paint. The colored lines are made slightly soft or sticky so that they will smear and create dark gray letters. Here’s a glass rod - try it yourself!” (...)
I said, “Okay. Still, I'll try. Bring me a rubber stamp and some Vaseline." They brought me a large, smooth, clean stamp of military censorship. I rubbed Vaseline on it, then wiped it off with a handkerchief until it stopped leaving marks on the paper. Then I pressed it tightly against the spy-proof paper, preventing it from sliding to the side.
“Can you spot the writing here?” - I asked.
They tested the paper in reflected and polarized light and said, “There’s nothing here.”
"Then let's shine it with ultraviolet rays." We took her into the booth and put her in front of my black window. On the paper, in bright blue letters, as if a stamp smeared with ink had been applied to it, glowed the words: “There are no secret inscriptions.”
Since ancient times, humanity has tried to invent invisible or, as they are also called, sympathetic ink, which is not visible to the eye under normal conditions, but begins to appear after exposure to any chemical elements, heating, ultraviolet rays. They were used to send secret messages, store important information, and secret correspondence.
In ancient times, these were publicly available substances that could be found in every home. For example, secret writing using milk was very successful, lemon juice, rice water, wax, apple and onion juice, rutabaga juice. Later, options for making sympathetic ink using aspirin tablets appeared, copper sulfate, iodine, washing powder.
Modern UV ink
Science does not stand still, so in our time you will no longer surprise anyone with invisible ink produced industrially. Compositions that glow under ultraviolet lamps are very popular. There are even pens with ultraviolet ink available for sale, which can be found in spy stores.
An alternative to such a pen can be invisible anti-counterfeiting paints and pigments. They are powdery substances that can be used to mark banknotes, securities, and clothing. In daylight, the powder is completely indistinguishable, but in ultraviolet light every grain or powder becomes visible.
How to make invisible fluorescent ink at home
As a good fluorescent ink, you can use regular washing powder, which contains optical brighteners. After diluting the powder with a small amount of water, you can begin to write a secret message. The dried solution will not leave imprints on the paper, but will be perfectly visible in the light of an ultraviolet lamp.
Can also be purchased separately. As a rule, they are used to impart whiteness with a bluish tint to clothing, fabrics, and paper intended for printing. The powder can also be used to create sympathetic ink. This ink appears on all types of paper.
Another way to make invisible ink is by using aspirin tablets and alcohol. IN small quantity alcohol should be dissolved 2-3 tablets of aspirin. If any sediment remains during dissolution, the liquid should be filtered. After this, you can begin secret writing. Such ink does not glow on all types of paper; this method is not applicable if you write on printer paper.
You can also use the following preparations to prepare ink, which you can try to purchase at the pharmacy:
- curcumin;
- quinine sulfate;
- trypoflamin.
Sodium fluorescein can also be used, but its native color may stand out on white paper after application, so this ink is not invisible.
An infectious disease caused by the fungus dermatophyte is called lichen. Microscopic organisms live on the skin, namely in the hair follicles. The fungus responsible for ringworm is found in the soil, which is why cats and cattle are most often infected with it. Controversy persists environment up to two years even gardening tools, shoes, carpets.
Children who try everything with their hands, and sometimes with their teeth, are susceptible to infection due to a weak immune system. The disease is transmitted to people through domestic animals or from an infected environment. Athlete's foot and groin are most often spread in public locker rooms and swimming pools.
Ringworm appears as a small lesion with scaly skin in the center. Gradually it grows, causing hair loss. The lesions are not always circular in shape, and the hair does not always fall out completely. Baldness may be accompanied by redness and inflammation. Hair can grow back 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 further directions for examination or confirm their own guesses.
Fluorescent lamp
Wood's lamp is a diagnostic tool in which the affected skin is exposed to a black light to cause a certain glow. Black light is waves in the ultraviolet spectrum, invisible to the naked eye, that glow violet in the dark.
The traditional Wood's lamp was equipped with a mercury coating to emit a wavelength of 320-450 nm and was invented in 1903 by physicist Robert Wood. Modern black light sources are developed based on fluorescent, mercury, light-emitting lamps, diodes or incandescent lamps. It is the dark blue coating on the tube that filters out most of the visible light waves.
Luminescent diagnostics
To diagnose skin problems under a Wood's lamp, you need to follow several steps:
- Wash your skin and remove makeup, moisturizers and other cosmetics, as they 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 of the lamp onto the skin at a distance of 10-30 cm.
Fluorescent color allows you to detect pigmented or depigmented spots.
Normal healthy skin glows light blue, thickened areas appear white and oily areas appear yellow, dehydrated skin turns purple.
To distinguish ringworm from other skin lesions, a Wood's lamp is used. The test result is positive if the pigmentation becomes more pronounced during the test.
Features of the glow
Fluorescent black becomes visible when collagen or porphyrins absorb it and emit it at visible wavelengths. Threads, hair, medication and soap residue on the skin may also fluoresce.
What color does ringworm glow 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 an increase in the level of melanin in the cells.
- Loss of pigmentation (vitiligo, tuberous sclerosis, hypomelanosis) should be identified in fair-skinned people. 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 influence of the fungus, and its spots become more pronounced under ultraviolet light.
- In folliculitis caused by Malassezia yeast, the hair follicles emit 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, which turns coral pink.
- Lichen planus is diagnosed by the appearance of whitish-yellow spots.
- Rosea and herpes zoster are examined using a Wood's lamp only for differential diagnosis. The herpes virus is confirmed by detecting DNA using polymerase chain reaction in the fluid that is taken from the rash blisters. Inflammatory processes are highlighted in white, which can also indicate an immune response to viruses or bacteria.
Wood's lamp guides diagnostics in the right direction. The most contagious type of fungus that causes lichen is microsporum. To confirm the infection, bacterial culture is carried out in laboratory conditions, which requires at least 10-14 days. Therefore, a fluorescent lamp with a Wood filter is used as a method of express diagnostics.
Fresh lesions of ringworm on the hair may not be detected with a lamp, since the signs of the lesion are minor. The dermatologist recommends removing hair from the suspected site of infection to examine the roots. Even after the death of the fungus, the hair continues to glow.
Diagnostic rules
Wood's lamp helps to identify foci of lichen on smooth skin, hair, nails, eyebrows. The dermatologist uses a protective mask or glasses to protect vision from direct radiation from 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 skin in detail.
It must be remembered that luminescent examination only complements the basic diagnosis and allows one to suspect a certain disease.
So, a lesion glowing white 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 can identify the shade of a particular pathology. At home, a Wood's lamp can refute or confirm the need to see a doctor if a rash appears on the body or head.
Ultraviolet treatment
If fungal infections can be diagnosed with ultraviolet lamps, then other skin lesions can be treated with the same type of physiotherapy. The herpes virus, which causes shingles, is sensitive to ultraviolet light. Therefore, dermatologists use physiotherapeutic procedures that contribute to the gradual disappearance of spots. Pityriasis rosea can be cured on your own, even in a solarium, if it does not respond to therapy and is prone to relapse.
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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 surroundings. Most things remained dark - they only slightly reflected the weak purple light of the lamp.
But some objects, inconspicuous in daylight, flashed brightly different colors. Most of it was blue. White wires and a colorless PVC tube, PET bottles and a plastic bucket glowed blue. The paper became bright white, with a bluish tint, and the orange plastic became even brighter. The colored stickers that were used as labels glowed. The white robe, shirt and some parts of the sweater glowed.
Recently I tried to conduct experiments with a UV lamp at home (in the absence of a laboratory). The impressions turned out to be completely different. If the walls of the laboratory were covered tiles and whitewashed, then the walls and ceiling of the house were covered with wallpaper.
Some of the wallpaper was paper - the paper glowed in the UV, but stains of glue, paint and other contaminants did not. As a result, the room looked unaesthetic: impurities that were barely noticeable in daylight and electric light came to the fore - dark spots on a luminous background. Dark brown furniture in ultraviolet light seemed light brown and ugly.
The oil paint in the bathroom looked downright scary, but in the bath itself I noticed bright blue spots - they glowed almost like a phosphor. It turned out that these were frozen pieces water-based paint, from which I washed the bucket. The paint looked white, but the bright glow in the 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's marks glowed green under 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 - with electric light.
In past experiments, the porcelain mortar that I photographed under UV light in the lab appeared dark purple (i.e., it simply reflected the dull purple rays of the lamp).
It turned out that white porcelain plates behave similarly, but it also turned out significant difference. Visually, the plates look almost clean, but as soon as you turn on the black light lamp, residues of dirt and debris become visible on the plate. detergent: The porcelain did not glow and the dirt and/or detergent glowed green.
The inner side of the hand looked light in the ultraviolet rays, but the outer side looked dark (like a black man's) - only the nails glowed. The difference is not very clearly visible in the photographs, because... when outside brush exposure was significantly longer.
The monitor screen (with a ray tube) glowed green in ultraviolet rays, and not particularly intensely. This is not surprising, since the phosphors applied to the kinescope screen are designed to glow under the influence of an electron beam, and not soft ultraviolet rays.
A toy mouse made of fabric 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 brightly that it was clearly visible even when the electric light was on.
But the colorless PVC tube glowed most brightly - it literally glowed blue, like a fluorescent lamp. There is no doubt about the presence of optical brighteners.
