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111-503: Blacklight sources may be specially designed fluorescent lamps , mercury-vapor lamps , light-emitting diodes (LEDs), lasers , or incandescent lamps . In medicine , forensics , and some other scientific fields, such a light source is referred to as a Wood's lamp, named after Robert Williams Wood , who invented the original Wood's glass UV filters. Although many other types of lamp emit ultraviolet light with visible light, blacklights are essential when UV-A light without visible light

222-699: A constant-voltage power supply , a fluorescent lamp would rapidly self-destruct because of the uncontrolled current flow. To prevent this, fluorescent lamps must use a ballast to regulate the current flow through the lamp. The terminal voltage across an operating lamp varies depending on the arc current, tube diameter, temperature, and fill gas. A general lighting service 48-inch (1,219 mm) T12 lamp operates at 430 mA, with 100 volts drop. High-output lamps operate at 800 mA, and some types operate up to 1.5 A. The power level varies from 33 to 82 watts per meter of tube length (10 to 25 W/ft) for T12 lamps. The simplest ballast for alternating current (AC) use

333-451: A Geissler tube. He went on to apply thin coatings of luminescent materials to the surfaces of these tubes. Fluorescence occurred, but the tubes were inefficient and had a short operating life. Inquiries that began with the Geissler tube continued as better vacuums were produced. The most famous was the evacuated tube used for scientific research by William Crookes . That tube was evacuated by

444-436: A Kill . Blacklight puppetry is performed in a blacklight theater. Blacklights are a common tool for rock-hunting and identification of minerals by their fluorescence. The most common minerals and rocks that glow under UV light are fluorite, calcite, aragonite, opal, apatite, chalcedony, corundum (ruby and sapphire), scheelite, selenite, smithsonite, sphalerite, sodalite. The first person to observe fluorescence in minerals

555-528: A UV filter coating such as Wood's glass on the envelope of a common incandescent bulb . This was the method that was used to create the very first blacklight sources. Although incandescent bulbs are a cheaper alternative to fluorescent tubes, they are exceptionally inefficient at producing UV light since most of the light emitted by the filament is visible light which must be blocked. Due to its black body spectrum, an incandescent light radiates less than 0.1% of its energy as UV light. Incandescent UV bulbs, due to

666-399: A capacitor. With no arc current, the transformer and capacitor resonate at line frequency and generate about twice the supply voltage across the tube, and a small electrode heating current. This tube voltage is too low to strike the arc with cold electrodes, but as the electrodes heat up to thermionic emission temperature, the tube striking voltage falls below that of the ringing voltage, and

777-488: A circular tube, used for table lamps or other places where a more compact light source is desired. Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, four, or six, or a small diameter tube coiled in a helix, to provide a high amount of light output in minimal volume. Light-emitting phosphors are applied as

888-475: A consequence of the current, the bulb operated at a higher temperature which necessitated the use of a quartz bulb. Although its light output relative to electrical consumption was better than that of other sources of light, the light it produced was similar to that of the Cooper-Hewitt lamp in that it lacked the red portion of the spectrum, making it unsuitable for ordinary lighting. Due to difficulties in sealing

999-464: A deformed tube or internal heat-sinks to control cold spot temperature and mercury distribution. Heavily loaded small lamps, such as compact fluorescent lamps, also include heat-sink areas in the tube to maintain mercury vapor pressure at the optimum value. Only a fraction of the electrical energy input into a lamp is converted to useful light. The ballast dissipates some heat; electronic ballasts may be around 90% efficient. A fixed voltage drop occurs at

1110-468: A fluorescent lamp in 1896 that used a coating of calcium tungstate as the fluorescing substance, excited by X-rays . Although it received a patent in 1907, it was not put into production. As with a few other attempts to use Geissler tubes for illumination, it had a short operating life, and given the success of the incandescent light, Edison had little reason to pursue an alternative means of electrical illumination. Nikola Tesla made similar experiments in

1221-521: A fluorescent lamp in 1919 and whose patent application was still pending. GE also had filed a patent application in 1936 in Inman's name to cover the “improvements” wrought by his group. In 1939 GE decided that the claim of Meyer, Spanner, and Germer had some merit, and that in any event a long interference procedure was not in their best interest. They therefore dropped the Buttolph claim and paid $ 180,000 to acquire

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1332-453: A heating current to the cathodes during operation, but the cold cathodes starting increases sputter, and they take much longer to transition from a glow discharge to an arc during warm up, thus the lifespan is typically about half of those seen in comparable rapid-start lamps. Because the formation of an arc requires the thermionic emission of large quantities of electrons from the cathode, rapid start ballast designs provide windings within

1443-504: A high-voltage power supply and a pressure-regulating system for the fill gas. Moore invented an electromagnetically controlled valve that maintained a constant gas pressure within the tube, to extend the working life. Although Moore's lamp was complicated, expensive, and required very high voltages, it was considerably more efficient than incandescent lamps, and it produced a closer approximation to natural daylight than contemporary incandescent lamps. From 1904 onwards Moore's lighting system

1554-518: A lamp for a short time when power is initially applied, and do not repeatedly attempt to restrike a lamp that is dead and unable to sustain an arc; some automatically stop trying to start a failed lamp. This eliminates the re-striking of a lamp and the continuous flashing of a failing lamp with a glow starter. Electronic starters are not subject to wear and do not need replacing periodically, although they may fail like any other electronic circuit. Manufacturers typically quote lives of 20 years, or as long as

1665-441: A layer of hydroxides and carbonates in contact with atmospheric moisture and carbon dioxide. The susceptibility to thermal shock makes manufacture of hermetically sealed glass bulbs difficult and costly. Therefore, most contemporary " black-light " bulbs are made of structurally more suitable glass with only a layer of a UV-filtering enamel on its surface; such bulbs, however, pass much more visible light, appearing brighter to

1776-445: A lower loading than their thermionic emission equivalents. Given the higher tube voltage required anyway, these tubes can easily be made long, and even run as series strings. They are better suited for bending into special shapes for lettering and signage, and can also be instantly switched on or off. The gas used in the fluorescent tube must be ionized before the arc can "strike" . For small lamps, it does not take much voltage to strike

1887-504: A metastable state by the impact of an electron, can impart energy to a mercury atom and ionize it, described as the Penning effect . This lowers the breakdown and operating voltage of the lamp, compared to other possible fill gases such as krypton. A fluorescent lamp tube is filled with a mix of argon , xenon , neon , or krypton , and mercury vapor. The pressure inside the lamp is around 0.3% of atmospheric pressure. The partial pressure of

1998-446: A paint-like coating to the inside of the tube. The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary; large grains lead to weak coatings, and small particles lead to poor light maintenance and efficiency. Most phosphors perform best with

2109-512: A particle size around 10 micrometers. The coating must be thick enough to capture all the ultraviolet light produced by the mercury arc, but not so thick that the phosphor coating absorbs too much visible light. The first phosphors were synthetic versions of naturally occurring fluorescent minerals, with small amounts of metals added as activators. Later other compounds were discovered, allowing differing colors of lamps to be made. Fluorescent tubes can have an outer silicone coating applied by dipping

2220-481: A photochemical reaction inside those substances. This process of hardening is called ‘curing’. UV curing is adaptable to printing, coating, decorating, stereolithography, and in the assembly of a variety of products and materials. In comparison to other technologies, curing with UV energy may be considered a low-temperature process, a high-speed process, and is a solventless process, as cure occurs via direct polymerization rather than by evaporation. Originally introduced in

2331-433: A purple filter material in the bulb. Plain glass blocks out less of the visible mercury emission spectrum, making them appear light blue-violet to the naked eye. These lamps are referred to by the designation "blacklight" or "BL" in some North American lighting catalogs. These types are not suitable for applications which require the low visible light output of "BLB" tubes lamps. A blacklight may also be formed by simply using

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2442-520: A reliable electrical discharge, and fluorescent coatings that could be energized by ultraviolet light. At this point, intensive development was more important than basic research. In 1934, Arthur Compton , a renowned physicist and GE consultant, reported to the GE lamp department on successful experiments with fluorescent lighting at General Electric Co., Ltd. in Great Britain (unrelated to General Electric in

2553-452: A result of avalanche ionization , the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp. The fill gas helps determine the electrical characteristics of the lamp but does not give off light itself. The fill gas effectively increases the distance that electrons travel through the tube, which allows an electron a greater chance of interacting with a mercury atom. Additionally, argon atoms, excited to

2664-411: A semiconductor switch and "soft start" the lamp by preheating the cathodes before applying a starting pulse which strikes the lamp first time without flickering; this dislodges a minimal amount of material from the cathodes during starting, giving longer lamp life. This is claimed to prolong lamp life by a factor of typically 3 to 4 times for a lamp frequently switched on as in domestic use, and to reduce

2775-581: A soft tip, that can be used to "invisibly" mark items. If the objects that are so marked are subsequently stolen, a blacklight can be used to search for these security markings. At some amusement parks , nightclubs and at other, day-long (or night-long) events, a fluorescent mark is rubber stamped onto the wrist of a guest who can then exercise the option of leaving and being able to return again without paying another admission fee. Fluorescent materials are also very widely used in numerous applications in molecular biology, often as "tags" which bind themselves to

2886-414: A substance of interest (for example, DNA), so allowing their visualization. Thousands of moth and insect collectors all over the world use various types of blacklights to attract moth and insect specimens for photography and collecting. It is one of the preferred light sources for attracting insects and moths at night. They can illuminate animal excreta, such as urine and vomit, that is not always visible to

2997-399: A thermal over-current trip to detect repeated starting attempts and disable the circuit until manually reset. A power factor correction (PFC) capacitor draws leading current from the mains to compensate for the lagging current drawn by the lamp circuit. Electronic starters use a different method to preheat the cathodes. They may be plug-in interchangeable with glow starters. They use

3108-437: Is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output (e.g. the luminous efficacy of an incandescent lamp may only be 16 lm/w). Fluorescent lamp fixtures are more costly than incandescent lamps because, among other things, they require a ballast to regulate current through the lamp, but the initial cost is offset by a much lower running cost. Compact fluorescent lamps made in

3219-440: Is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, to produce ultraviolet and make a phosphor coating in the lamp glow. Fluorescent lamps convert electrical energy into useful light much more efficiently than incandescent lamps , but are less efficient than most LED lamps . The typical luminous efficacy of fluorescent lamps

3330-517: Is absorbed less and reaches deeper into skin layers , where it produces reactive chemical intermediates such as hydroxyl and oxygen radicals , which in turn can damage DNA and result in a risk of melanoma . The weak output of blacklights is not sufficient to cause DNA damage or cellular mutations in the way that direct summer sunlight can, although there are reports that overexposure to the type of UV radiation used for creating artificial suntans on sunbeds can cause DNA damage, photo-aging (damage to

3441-800: Is also helpful in diagnosing: A Wood's lamp may be used to rapidly assess whether an individual is suffering from ethylene glycol poisoning as a consequence of antifreeze ingestion. Manufacturers of ethylene glycol-containing antifreezes commonly add fluorescein , which causes the patient's urine to fluoresce under Wood's lamp. Wood's lamp is useful in diagnosing conditions such as tuberous sclerosis and erythrasma (caused by Corynebacterium minutissimum , see above). Additionally, detection of porphyria cutanea tarda can sometimes be made when urine turns pink upon illumination with Wood's lamp. Wood's lamps have also been used to differentiate hypopigmentation from depigmentation such as with vitiligo . A vitiligo patient's skin will appear yellow-green or blue under

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3552-505: Is an inductor placed in series, consisting of a winding on a laminated magnetic core. The inductance of this winding limits the flow of AC current. This type of ballast is common in 220–240V countries (And in North America, up to 30W lamps). Ballasts are rated for the size of lamp and power frequency. In North America, the AC voltage is insufficient to start long fluorescent lamps, so the ballast

3663-450: Is attached to the outside of the lamp glass. This ballast type is incompatible with the European energy saver T8 fluorescent lamps because these lamps require a higher starting voltage than that of the open circuit voltage of rapid start ballasts. Quick-start ballasts use a small auto-transformer to heat the filaments when power is first applied. When an arc strikes, the filament heating power

3774-405: Is becoming outdated (as of 2010), while the (German) Osram system is becoming dominant outside North America. The following table lists the tubes generating blue, UVA and UVB, in order of decreasing wavelength of the most intense peak. Approximate phosphor compositions, major manufacturer's type numbers and some uses are given as an overview of the types available. "Peak" position is approximated to

3885-533: Is called fluorescence , and has many practical uses. Blacklights are required to observe fluorescence, since other types of ultraviolet lamps emit visible light which drowns out the dim fluorescent glow. A Wood's lamp is a diagnostic tool used in dermatology by which ultraviolet light is shone (at a wavelength of approximately 365 nanometers) onto the skin of the patient; a technician then observes any subsequent fluorescence . For example, porphyrins —associated with some skin diseases—will fluoresce pink. Though

3996-547: Is critically affected by the temperature of the bulb wall and its effect on the partial pressure of the mercury vapor within. Since mercury condenses at the coolest spot in the lamp, careful design is required to maintain that spot at the optimum temperature, around 40 °C (104 °F). Using an amalgam with some other metal reduces the vapor pressure and increases the optimum temperature range. The bulb wall "cold spot" temperature must still be controlled to prevent condensing. High-output fluorescent lamps have features such as

4107-409: Is needed, particularly in observing fluorescence , the colored glow that many substances emit when exposed to UV. They are employed for decorative and artistic lighting effects, diagnostic and therapeutic uses in medicine, the detection of substances tagged with fluorescent dyes , rock-hunting , scorpion-hunting, the detection of counterfeit money , the curing of plastic resins, attracting insects and

4218-418: Is not stable. The atom will emit an ultraviolet photon as the atom's electron reverts to a lower, more stable, energy level. Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 and 185 nanometers (nm). These are not visible to the human eye, so ultraviolet energy is converted to visible light by

4329-412: Is often a step-up autotransformer with substantial leakage inductance (to limit current flow). Either form of inductive ballast may also include a capacitor for power factor correction. Fluorescent lamps can run directly from a direct current (DC) supply of sufficient voltage to strike an arc. The ballast must be resistive, and would consume about as much power as the lamp. When operated from DC,

4440-524: Is reduced and the tube will start within half a second. The auto-transformer is either combined with the ballast or may be a separate unit. Tubes need to be mounted near an earthed metal reflector in order for them to strike. Quick-start ballasts are more common in commercial installations because of lower maintenance costs. A quick-start ballast eliminates the need for a starter switch, a common source of lamp failures. Nonetheless, Quick-start ballasts are also used in domestic (residential) installations because of

4551-674: Is special barium - sodium - silicate glass incorporating about 9% nickel oxide . It is a very deep violet-blue glass, opaque to all visible light rays except longest red and shortest violet. It is quite transparent in the violet/ultraviolet in a band between 320 and 400 nanometres with a peak at 365 nanometres, and a fairly broad range of infrared and the longest, least visible red wavelengths. Wood's glass has lower mechanical strength and higher thermal expansion than commonly used glasses, making it more vulnerable to thermal shocks and mechanical damage. The nickel and barium oxides are also chemically reactive, with tendency to slowly form

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4662-498: Is that less space needs to be devoted to storing items which can not be used until the drying step is finished. Because UV energy has unique interactions with many different materials, UV curing allows for the creation of products with characteristics not achievable via other means. This has led to UV curing becoming fundamental in many fields of manufacturing and technology, where changes in strength, hardness, durability, chemical resistance, and many other properties are required. One of

4773-417: Is then run in order to circulate the dye across the piping and components and then the system is examined with a blacklight lamp. Any evidence of fluorescent dye then pinpoints the leaking part which needs replacement. Blacklight is used to illuminate pictures painted with fluorescent colors, particularly on black velvet , which intensifies the illusion of self-illumination. The use of such materials, often in

4884-495: The Geissler tube , consisting of a partially evacuated glass tube with a metal electrode at either end. When a high voltage was applied between the electrodes, the inside of the tube illuminated with a glow discharge . By putting different chemicals inside, the tubes could be made to produce a variety of colors, and elaborate Geissler tubes were sold for entertainment. More important was its contribution to scientific research. One of

4995-412: The fluorescence of the inner phosphor coating. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon heats the phosphor coating. Electric current flows through the tube in a low-pressure arc discharge . Electrons collide with and ionize noble gas atoms inside the bulb surrounding the filament to form a plasma by the process of impact ionization . As

5106-534: The 1890s, devising high-frequency powered fluorescent bulbs that gave a bright greenish light, but as with Edison's devices, no commercial success was achieved. One of Edison's former employees created a gas-discharge lamp that achieved a measure of commercial success. In 1895 Daniel McFarlan Moore demonstrated lamps 2 to 3 meters (6.6 to 9.8 ft) in length that used carbon dioxide or nitrogen to emit white or pink light, respectively. They were considerably more complicated than an incandescent bulb, requiring both

5217-498: The 1960s, this technology has streamlined and increased automation in many industries in the manufacturing sector. A primary advantage of curing with ultraviolet light is the speed at which a material can be processed. Speeding up the curing or drying step in a process can reduce flaws and errors by decreasing time that an ink or coating spends wet. This can increase the quality of a finished item, and potentially allow for greater consistency. Another benefit to decreasing manufacturing time

5328-519: The Hull patent gave GE a basis for claiming legal rights over the fluorescent lamp, a few months after the lamp went into production the firm learned of a U.S. patent application that had been filed in 1927 for the aforementioned "metal vapor lamp" invented in Germany by Meyer, Spanner, and Germer. The patent application indicated that the lamp had been created as a superior means of producing ultraviolet light, but

5439-500: The Meyer, et al. application, which at that point was owned by a firm known as Electrons, Inc. The patent was duly awarded in December 1939. This patent, along with the Hull patent, put GE on what seemed to be firm legal ground, although it faced years of legal challenges from Sylvania Electric Products , Inc., which claimed infringement on patents that it held. Even though the patent issue

5550-498: The UV photons that generated them (a phenomenon called Stokes shift ). Incident photons have an energy of 5.5 electron volts but produce visible light photons with energy around 2.5 electron volts, so only 45% of the UV energy is used; the rest is dissipated as heat. Most fluorescent lamps use electrodes that emit electrons into the tube by heat, known as hot cathodes. However, cold cathode tubes have cathodes that emit electrons only due to

5661-525: The UVB range. UVA is the safest of the three spectra of UV light , although high exposure to UVA has been linked to the development of skin cancer in humans. The relatively low energy of UVA light does not cause sunburn . It can damage collagen fibers, so may accelerate skin aging and cause wrinkles . It can also degrade vitamin A in the skin. UVA light has been shown to cause DNA damage , but not directly, like UVB and UVC. Due to its longer wavelength , it

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5772-470: The United States lamps up to about 30 watts). Before the 1960s, four-pin thermal starters and manual switches were used. A glow switch starter automatically preheats the lamp cathodes. It consists of a normally open bi-metallic switch in a small sealed gas-discharge lamp containing inert gas (neon or argon). The glow switch will cyclically warm the filaments and initiate a pulse voltage to strike

5883-552: The United States). Stimulated by this report, and with all of the key elements available, a team led by George E. Inman built a prototype fluorescent lamp in 1934 at General Electric 's Nela Park (Ohio) engineering laboratory. This was not a trivial exercise; as noted by Arthur A. Bright, "A great deal of experimentation had to be done on lamp sizes and shapes, cathode construction, gas pressures of both argon and mercury vapor, colors of fluorescent powders, methods of attaching them to

5994-453: The Wood's lamp. Its use in detecting melanoma has been reported. Blacklight is commonly used to authenticate oil paintings , antiques and banknotes . It can also differentiate real currency from counterfeit notes because, in many countries, legal banknotes have fluorescent symbols on them that only show under a blacklight. In addition, the paper used for printing money does not contain any of

6105-411: The application also contained a few statements referring to fluorescent illumination. Efforts to obtain a U.S. patent had met with numerous delays, but were it to be granted, the patent might have caused serious difficulties for GE. At first, GE sought to block the issuance of a patent by claiming that priority should go to one of their employees, Leroy J. Buttolph, who according to their claim had invented

6216-421: The arc and starting the lamp presents no problem, but larger tubes require a substantial voltage (in the range of a thousand volts). Many different starting circuits have been used. The choice of circuit is based on cost, AC voltage, tube length, instant versus non-instant starting, temperature ranges and parts availability. Preheating, also called switchstart, uses a combination filament – cathode at each end of

6327-469: The arc strikes. As the electrodes heat, the lamp slowly, over three to five seconds, reaches full brightness. As the arc current increases and tube voltage drops, the circuit provides current limiting. Wood%27s glass Wood's glass is an optical filter glass invented in 1903 by American physicist Robert Williams Wood (1868–1955), which allows ultraviolet and infrared light to pass through, while blocking most visible light. Wood's glass

6438-400: The arc; the process repeats until the lamp is lit. Once the tube strikes, the impinging main discharge keeps the cathodes hot, permitting continued electron emission. The starter switch does not close again because the voltage across the lit tube is insufficient to start a glow discharge in the starter. With glow switch starters a failing tube will cycle repeatedly. Some starter systems used

6549-411: The ballast that continuously warm the cathode filaments. Usually operating at a lower arc voltage than the instant start design; no inductive voltage spike is produced for starting, so the lamps must be mounted near a grounded (earthed) reflector to allow the glow discharge to propagate through the tube and initiate the arc discharge via capacitive coupling . In some lamps a grounded "starting aid" strip

6660-432: The best sources of fluorite in mines or potential new mines. Some transparent selenite crystals exhibit an “hourglass” pattern under UV light that is not visible in natural light. These crystals are also phosphorescent. Limestone, marble, and travertine can glow because of calcite presence. Granite, syenite, and granitic pegmatite rocks can also glow. UV light can be used to harden particular glues, resins and inks by causing

6771-484: The blackening of the ends of the lamp typical of fluorescent tubes. While the circuit is complex, the complexity is built into an integrated circuit chip. Electronic starters may be optimized for fast starting (typical start time of 0.3 seconds), or for most reliable starting even at low temperatures and with low supply voltages, with a startup time of 2–4 seconds. The faster-start units may produce audible noise during start-up. Electronic starters only attempt to start

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6882-411: The brightening agents which cause commercially available papers to fluoresce under blacklight. Both of these features make illegal notes easier to detect and more difficult to successfully counterfeit. The same security features can be applied to identification cards such as passports or driver's licenses . Other security applications include the use of pens containing a fluorescent ink, generally with

6993-406: The conversion of electrical energy to light is the emission of a photon when an electron in a mercury atom falls from an excited state into a lower energy level . Electrons flowing in the arc collide with the mercury atoms. If the incident electron has enough kinetic energy , it transfers energy to the atom's outer electron, causing that electron to temporarily jump up to a higher energy level that

7104-411: The desirable feature that a Quick-start ballast light turns on nearly immediately after power is applied (when a switch is turned on). Quick-start ballasts are used only on 240 V circuits and are designed for use with the older, less efficient T12 tubes. The semi-resonant start circuit was invented by Thorn Lighting for use with T12 fluorescent tubes. This method uses a double wound transformer and

7215-511: The detection of refrigerant leaks affecting refrigerators and air conditioning systems. Strong sources of long-wave ultraviolet light are used in tanning beds . UV-A presents a potential hazard when eyes and skin are exposed, especially to high power sources. According to the World Health Organization , UV-A is responsible for the initial tanning of skin and it contributes to skin ageing and wrinkling. UV-A may also contribute to

7326-511: The discharge becomes an arc. These tubes have no filaments and can be identified by a single pin at each end of the tube (for common lamps; compact cold-cathode lamps may also have a single pin, but operate from a transformer rather than a ballast). The lamp holders have a "disconnect" socket at the low-voltage end which disconnects the ballast when the tube is removed, to prevent electric shock . Instant-start lamps are slightly more energy efficient than rapid start, because they do not constantly send

7437-538: The electrode may still occur, but electrodes can be shaped (e.g. into an internal cylinder) to capture most of the sputtered material so it is not lost from the electrode. Cold cathode lamps are generally less efficient than thermionic emission lamps because the cathode fall voltage is much higher. Power dissipated due to cathode fall voltage does not contribute to light output. However, this is less significant with longer tubes. The increased power dissipation at tube ends also usually means cold cathode tubes have to be run at

7548-406: The electrodes to the quartz, the lamp had a short life. The next step in gas-based lighting took advantage of the luminescent qualities of neon , an inert gas that had been discovered in 1898 by isolation from the atmosphere. Neon glowed a brilliant red when used in Geissler tubes. By 1910, Georges Claude , a Frenchman who had developed a technology and a successful business for air liquefaction,

7659-403: The electrodes, which also produces heat. Some of the energy in the mercury vapor column is also dissipated, but about 85% is turned into visible and ultraviolet light. Not all the UV radiation striking the phosphor coating is converted to visible light; some energy is lost. The largest single loss in modern lamps is due to the lower energy of each photon of visible light, compared to the energy of

7770-427: The emission peaks are broad, so only the very lowest energy UV photons are emitted, within predominant not visible light. Although blacklights produce light in the UV range, their spectrum is mostly confined to the longwave UVA region, that is, UV radiation nearest in wavelength to visible light, with low frequency and therefore relatively low energy. While low, there is still some power of a conventional blacklight in

7881-595: The eye. Due to manufacturing difficulties, Wood's glass is now more commonly used in standalone flat or dome-shaped filters, instead of being the material of the light bulb. With prolonged exposure to ultraviolet radiation, Wood's glass undergoes solarization , gradually losing transparency for UV. Photographic filters for ultraviolet photography , notably the Kodak Wratten 18A and 18B, are based on Wood's glass. Bulbs made of Wood's glass are potentially hazardous in comparison with those made of enameled glass, since

7992-445: The eyes and skin. A few other spectral lines, falling within the pass band of the Wood's glass between 300 and 400 nm, contribute to the output. These lamps are used mainly for theatrical purposes and concert displays. They are more efficient UVA producers per unit of power consumption than fluorescent tubes. Ultraviolet light can be generated by some light-emitting diodes , but wavelengths shorter than 380 nm are uncommon, and

8103-413: The first scientists to experiment with a Geissler tube was Julius Plücker , who systematically described in 1858 the luminescent effects that occurred in a Geissler tube. He also made the important observation that the glow in the tube shifted position when in proximity to an electromagnetic field . Alexandre Edmond Becquerel observed in 1859 that certain substances gave off light when they were placed in

8214-488: The fluorescent lamp in their incorporation of a ballast to maintain a constant current. Cooper-Hewitt had not been the first to use mercury vapor for illumination, as earlier efforts had been mounted by Way, Rapieff, Arons, and Bastian and Salisbury. Of particular importance was the mercury-vapor lamp invented by Küch and Retschinsky in Germany . The lamp used a smaller bore bulb and higher current operating at higher pressures. As

8325-508: The form of tiles viewed in a sensory room under UV light, is common in the United Kingdom for the education of students with profound and multiple learning difficulties. Such fluorescence from certain textile fibers, especially those bearing optical brightener residues, can also be used for recreational effect, as seen, for example, in the opening credits of the James Bond film A View to

8436-537: The highly effective mercury vacuum pump created by Hermann Sprengel . Research conducted by Crookes and others ultimately led to the discovery of the electron in 1897 by J. J. Thomson and X-rays in 1895 by Wilhelm Röntgen . The Crookes tube , as it came to be known, produced little light because the vacuum in it was too great and thus lacked the trace amounts of gas that are needed for electrically stimulated luminescence . Thomas Edison briefly pursued fluorescent lighting for its commercial potential. He invented

8547-454: The idea and Edison used calcium tungstate for his unsuccessful lamp. Other efforts had been mounted, but all were plagued by low efficiency and various technical problems. Of particular importance was the invention in 1927 of a low-voltage “metal vapor lamp” by Friedrich Meyer, Hans-Joachim Spanner, and Edmund Germer , who were employees of a German firm in Berlin . A German patent was granted but

8658-431: The industry, has a dark blue filter coating on the tube, which filters out most visible light, so that fluorescence effects can be observed. These tubes have a dim violet glow when operating. They should not be confused with "blacklight" or "BL" tubes, which have no filter coating, and have a brighter blue color. These are made for use in " bug zapper " insect traps where the emission of visible light does not interfere with

8769-463: The innovations for night and all-weather flying used by the US, UK, Japan and Germany during World War II was the use of UV interior lighting to illuminate the instrument panel, giving a safer alternative to the radium -painted instrument faces and pointers, and an intensity that could be varied easily and without visible illumination that would give away an aircraft's position. This went so far as to include

8880-423: The inside of the tube, and other details of the lamp and its auxiliaries before the new device was ready for the public." In addition to having engineers and technicians along with facilities for R&D work on fluorescent lamps, General Electric controlled what it regarded as the key patents covering fluorescent lighting, including the patents originally issued to Hewitt, Moore, and Küch. More important than these

8991-429: The intensified and slightly broadened 350–375 nm spectral line of mercury from high pressure discharge at between 5 and 10 standard atmospheres (500 and 1,000 kPa), depending upon the specific type. These lamps use envelopes of Wood's glass or similar optical filter coatings to block out all the visible light and also the short wavelength (UVC) lines of mercury at 184.4 and 253.7 nm, which are harmful to

9102-535: The inventive efforts that supported them were of considerable value when the firm took up fluorescent lighting more than two decades later. At about the same time that Moore was developing his lighting system, Peter Cooper Hewitt invented the mercury-vapor lamp , patented in 1901 ( US 682692   ). Hewitt's lamp glowed when an electric current was passed through mercury vapor at a low pressure. Unlike Moore's lamps, Hewitt's were manufactured in standardized sizes and operated at low voltages. The mercury-vapor lamp

9213-483: The lamp in conjunction with a mechanical or automatic ( bi-metallic ) switch (see circuit diagram to the right) that initially connect the filaments in series with the ballast to preheat them; after a short preheating time the starting switch opens. If timed correctly relative to the phase of the supply AC, this causes the ballast to induce a voltage over the tube high enough to initiate the starting arc. These systems are standard equipment in 200–240 V countries (and in

9324-419: The lamp never went into commercial production. All the major features of fluorescent lighting were in place at the end of the 1920s. Decades of invention and development had provided the key components of fluorescent lamps: economically manufactured glass tubing, inert gases for filling the tubes, electrical ballasts, long-lasting electrodes, mercury vapor as a source of luminescence, effective means of producing

9435-418: The large voltage between the electrodes. The cathodes will be warmed by current flowing through them, but are not hot enough for significant thermionic emission . Because cold cathode lamps have no thermionic emission coating to wear out, they can have much longer lives than hot cathode tubes. This makes them desirable for long-life applications (such as backlights in liquid crystal displays ). Sputtering of

9546-446: The light fitting. Instant start fluorescent tubes were invented in 1944. Instant start simply uses a high enough voltage to break down the gas column and thereby start arc conduction. Once the high-voltage spark "strikes" the arc, the current is boosted until a glow discharge forms. As the lamp warms and pressure increases, the current continues to rise and both resistance and voltage falls, until mains or line-voltage takes over and

9657-612: The mercury vapor alone is about 0.8 Pa (8 millionths of atmospheric pressure), in a T12 40-watt lamp. The inner surface of the lamp is coated with a fluorescent coating made of varying blends of metallic and rare-earth phosphor salts. The lamp's electrodes are typically made of coiled tungsten and are coated with a mixture of barium, strontium and calcium oxides to improve thermionic emission . Fluorescent lamp tubes are often straight and range in length from about 100 millimeters (3.9 in) for miniature lamps, to 2.43 meters (8.0 ft) for high-output lamps. Some lamps have

9768-403: The naked eye. Blacklight is used extensively in non-destructive testing. Fluorescing fluids are applied to metal structures and illuminated, allowing easy detection of cracks and other weaknesses. If a leak is suspected in a refrigerator or an air conditioning system, a UV tracer dye can be injected into the system along with the compressor lubricant oil and refrigerant mixture. The system

9879-452: The nature of electricity and light phenomena as developed by the British scientists Michael Faraday in the 1840s and James Clerk Maxwell in the 1860s. Little more was done with this phenomenon until 1856 when German glassblower Heinrich Geissler created a mercury vacuum pump that evacuated a glass tube to an extent not previously possible. Geissler invented the first gas-discharge lamp,

9990-466: The nearest 10 nm. "Width" is the measure between points on the shoulders of the peak that represent 50% intensity. Another class of UV fluorescent bulb is designed for use in bug zappers . Insects are attracted to the UV light, which they are able to see, and are then electrocuted by the device. These bulbs use the same UV-A emitting phosphor blend as the filtered blacklight, but since they do not need to suppress visible light output, they do not use

10101-458: The necessary absorption of the visible light, become very hot during use. This heat is, in fact, encouraged in such bulbs, since a hotter filament increases the proportion of UVA in the black-body radiation emitted. This high running-temperature reduces the life of the lamp from a typical 1,000 hours to around 100 hours. High-power mercury vapor blacklight lamps are made in power ratings of 100 to 1,000 watts. These do not use phosphors, but rely on

10212-462: The neon light also was significant for the last key element of the fluorescent lamp, its fluorescent coating. In 1926 Jacques Risler received a French patent for the application of fluorescent coatings to neon light tubes. The main use of these lamps, which can be considered the first commercially successful fluorescents, was for advertising, not general illumination. This, however, was not the first use of fluorescent coatings; Becquerel had earlier used

10323-562: The performance of the product. The phosphor typically used for a near 368 to 371 nanometer emission peak is either europium -doped strontium fluoroborate ( SrB 2 F 8 : Eu ) or europium-doped strontium borate ( Sr 3 B 2 O 6 : Eu ) while the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate ( BaSi 2 O 5 : Pb ). "Blacklight blue" lamps peak at 365 nm. Manufacturers use different numbering systems for blacklight tubes. Philips'

10434-527: The printing of charts that were marked in UV-fluorescent inks, and the provision of UV-visible pencils and slide rules such as the E6B . They may also be used to test for LSD , which fluoresces under blacklight while common substitutes such as 25I-NBOMe do not. Strong sources of long-wave ultraviolet light are used in tanning beds . Fluorescent lamp A fluorescent lamp , or fluorescent tube ,

10545-422: The progression of skin cancers. Additionally, UV-A can have negative effects on eyes in both the short-term and long-term. Fluorescent blacklight tubes are typically made in the same fashion as normal fluorescent tubes except that a phosphor that emits UVA light instead of visible white light is used on the inside of the tube. The type most commonly used for blacklights, designated blacklight blue or "BLB" by

10656-573: The same sizes as incandescent lamp bulbs are used as an energy-saving alternative to incandescent lamps in homes. In the United States , fluorescent lamps are classified as universal waste . The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal, and some jurisdictions require recycling of them. The fluorescence of certain rocks and other substances had been observed for hundreds of years before its nature

10767-425: The skin from prolonged exposure to sunlight), toughening of the skin, suppression of the immune system, cataract formation and skin cancer. UV-A can have negative effects on eyes in both the short-term and long-term. Ultraviolet radiation is invisible to the human eye, but illuminating certain materials with UV radiation causes the emission of visible light, causing these substances to glow with various colors. This

10878-471: The starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube. Fluorescent lamps are (almost) never operated directly from DC for those reasons. Instead, an inverter converts the DC into AC and provides the current-limiting function as described below for electronic ballasts. The performance of fluorescent lamps

10989-405: The technique for producing a source of ultraviolet light was devised by Robert Williams Wood in 1903 using " Wood's glass ", it was in 1925 that the technique was used in dermatology by Margarot and Deveze for the detection of fungal infection of hair. It has many uses, both in distinguishing fluorescent conditions from other conditions and in locating the precise boundaries of the condition. It

11100-460: The tube into a solution of water and silicone, and then drying the tube. This coating gives the tube a silky surface finish, and protects against moisture, guaranteeing a predictable surface resistance on the tube when starting it. Fluorescent lamps are negative differential resistance devices, so as more current flows through them, the electrical resistance of the fluorescent lamp drops, allowing for even more current to flow. Connected directly to

11211-527: Was George Stokes in 1852. He noted the ability of fluorite to produce a blue glow when illuminated with ultraviolet light and called this phenomenon “fluorescence” after the mineral fluorite. Lamps used to visualise seams of fluorite and other fluorescent minerals are commonly used in mines but they tend to be on an industrial scale. The lamps need to be short wavelength to be useful for this purpose and of scientific grade. UVP range of hand held UV lamps are ideal for this purpose and are used by Geologists to identify

11322-568: Was a patent covering an electrode that did not disintegrate at the gas pressures that ultimately were employed in fluorescent lamps. Albert W. Hull of GE's Schenectady Research Laboratory filed for a patent on this invention in 1927, which was issued in 1931. General Electric used its control of the patents to prevent competition with its incandescent lights and probably delayed the introduction of fluorescent lighting by 20 years. Eventually, war production required 24-hour factories with economical lighting, and fluorescent lights became available. While

11433-666: Was by Westinghouse and General Electric and Showcase/Display Case fixtures were introduced by Artcraft Fluorescent Lighting Corporation in 1946. During the following year, GE and Westinghouse publicized the new lights through exhibitions at the New York World's Fair and the Golden Gate International Exposition in San Francisco. Fluorescent lighting systems spread rapidly during World War II as wartime manufacturing intensified lighting demand. By 1951 more light

11544-528: Was developed as a light filter used in communications during World War I . The glass filter worked both in infrared daylight communication and ultraviolet night communications by removing the visible components of a light beam, leaving only the "invisible radiation" as a signal beam. Wood's glass was commonly used to form the envelope for fluorescent and incandescent ultraviolet bulbs (" black lights "). In recent years, due to its disadvantages, other filter materials have largely replaced it. Wood's glass

11655-430: Was installed in a number of stores and offices. Its success contributed to General Electric 's motivation to improve the incandescent lamp, especially its filament. GE's efforts came to fruition with the invention of a tungsten -based filament. The extended lifespan and improved efficacy of incandescent bulbs negated one of the key advantages of Moore's lamp, but GE purchased the relevant patents in 1912. These patents and

11766-504: Was not completely resolved for many years, General Electric's strength in manufacturing and marketing gave it a pre-eminent position in the emerging fluorescent light market. Sales of "fluorescent lumiline lamps" commenced in 1938 when four different sizes of tubes were put on the market. They were used in fixtures manufactured by three leading corporations: Lightolier , Artcraft Fluorescent Lighting Corporation , and Globe Lighting. The Slimline fluorescent ballast's public introduction in 1946

11877-458: Was obtaining enough neon as a byproduct to support a neon lighting industry. While neon lighting was used around 1930 in France for general illumination, it was no more energy-efficient than conventional incandescent lighting. Neon tube lighting, which also includes the use of argon and mercury vapor as alternative gases, came to be used primarily for eye-catching signs and advertisements. Neon lighting

11988-423: Was produced in the United States by fluorescent lamps than by incandescent lamps. In the first years zinc orthosilicate with varying content of beryllium was used as greenish phosphor. Small additions of magnesium tungstate improved the blue portion of the spectrum, yielding acceptable white. After the discovery that beryllium was toxic , halophosphate-based phosphors dominated. The fundamental mechanism for

12099-444: Was relevant to the development of fluorescent lighting, however, as Claude's improved electrode (patented in 1915) overcame "sputtering", a major source of electrode degradation. Sputtering occurred when ionized particles struck an electrode and tore off bits of metal. Although Claude's invention required electrodes with a lot of surface area, it showed that a major impediment to gas-based lighting could be overcome. The development of

12210-592: Was superior to the incandescent lamps of the time in terms of energy efficiency , but the blue-green light it produced limited its applications. It was, however, used for photography and some industrial processes. Mercury vapor lamps continued to be developed at a slow pace, especially in Europe. By the early 1930s they received limited use for large-scale illumination. Some of them employed fluorescent coatings, but these were used primarily for color correction and not for enhanced light output. Mercury vapor lamps also anticipated

12321-493: Was understood. One of the first to explain it was Irish scientist Sir George Stokes from the University of Cambridge in 1852, who named the phenomenon "fluorescence" after fluorite , a mineral many of whose samples glow strongly because of impurities. By mid-19th century, experimenters had observed a radiant glow emanating from partially evacuated glass vessels through which an electric current passed. The explanation relied on

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