Inquiries that began with the Geissler tube continued as even better vacuums were produced. The most famous was the evacuated tube used for scientific research by William Crookes. That tube was evacuated by 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. But the Crookes tube, as it came to be known, produced little light because the vacuum in it was too good 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 a fluorescent lamp in 1896 that used a coating of calcium tungstate as the fluorescing substance, excited by X-rays, but 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 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.
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 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.
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 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.
Light-emitting phosphors are applied as 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 leads to poor light maintenance and efficiency. Most phosphors perform best with 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.
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 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 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.
Compared with an incandescent lamp, a fluorescent tube is a more diffuse and physically larger light source. In suitably designed lamps, light can be more evenly distributed without point source of glare such as seen from an undiffused incandescent filament; the lamp is large compared to the typical distance between lamp and illuminated surfaces.
Germicidal lamps contain no phosphor at all, making them mercury vapor gas discharge lamps rather than fluorescent. Their tubes are made of fused quartz transparent to the UVC light emitted by the mercury discharge. The 254 nm UVC emitted by these tubes will kill germs and the 184.45 nm far UV will ionize oxygen to ozone. Lamps labeled OF block the 184.45 nm far UV and do not produce significant ozone. In addition the UVC can cause eye and skin damage. They are sometimes used by geologists to identify certain species of minerals by the color of their fluorescence when fitted with filters that pass the short-wave UV and block visible light produced by the mercury discharge. They are also used in some EPROM erasers. Germicidal lamps have designations beginning with G, for example G30T8 for a 30-watt, 1-inch (2.5 cm) diameter, 36-inch (91 cm) long germicidal lamp (as opposed to an F30T8, which would be the fluorescent lamp of the same size and rating).
Fluorescent lamps can be illuminated by means other than a proper electrical connection. These other methods, however, result in very dim or very short-lived illumination, and so are seen mostly in science demonstrations. Static electricity or a Van de Graaff generator will cause a lamp to flash momentarily as it discharges a high-voltage capacitance. A Tesla coil will pass high-frequency current through the tube, and since it has a high voltage as well, the gases within the tube will ionize and emit light. This also works with plasma globes. Capacitive coupling with high-voltage power lines can light a lamp continuously at low intensity, depending on the intensity of the electric field.
While some gas discharge lamps are specifically made for emitting mostly ultraviolet light, others produce some unwanted ultraviolet light in addition to the actually used visible light.That may not only constitute a loss of energy, but also have negative side effects concerning human skin and eyes.In extreme cases, there can even be problems with intense ozone generation, which is particularly problematic for indoor use.Therefore, it is sometimes preferable to use ozone-free lamps, where the UV emission is minimized e.g. with a UV-absorbing dopant (e.g. titanium oxide or cerium oxide) in the tube glass, or by operating the lamp in a nitrogen atmosphere, because ozone can be generated only by irradiating oxygen.Note, however, that even an ozone-free lamp may exhibit some UV emission, e.g. outside the spectral range contributing to ozone generation.
Some constructions involve water cooling for the electrodes, or at least the anode, which often gets hotter.In some cases, for example for some lamp-pumped lasers, the whole lamp is surrounded by deionized cooling water (having a low electrical conductivity).Here, the lamp is often surrounded by a flow tube made of glass which contains the cooling water while transmitting the generated light.
Switching power supplies are obviously more efficient than the linear ones because of their \"0/1\" (ON/OFF switching) modulation. They can be designed to deliver high power efficiency as well as flicker-free illumination while maintaining a high power factor and low total harmonic distortion (THD). While linear LED drivers have been envisioned to be a prospective LED driving solution, SMPS is, for the foreseeable future, still the preferred LED driving solution for applications where efficiency, lighting control, light quality, and electrical safety are of paramount concern. In particular, the digital controllability of SMPS drivers, which are equipped with smart sensor technology and wireless connectivity, promises to enable a variety of Internet of Things (IoT) applications. Digital modulation allows encoding the data in binary for high-speed optical wireless communication (LiFi), which vastly expands the application potential of SMPS drivers.
DALI, with the ability to provide addressing of individual fixtures and status feedback from the loads, provides great flexibility in lighting control through a 4-wire (Hot and Neutral, plus 2 low-voltage data link topology-free wires) system. DALI is typically used where the control strategy requires the light fixture to respond to more than one controller (e.g., a manual control switch and an occupancy sensor). DALI is a bidirectional protocol and a DALI lighting system can operate up to 64 control points (drivers, dimmers, relays) without using a central control unit. The DALI protocol uses logarithmic dimming which provides 256 steps of brightness with a standardized dimming curve in the range of 0.1% to 100%. 1e1e36bf2d