Lighting mercury vapor

Electroluminescence. The emission of light as a consequence of electrical discharge in gases. Typical examples are neon lights, mercury vapor lamps and lightning Refs 1) CondChemDict (1961), 434-R 2) H.K. Hanisch, "Electroluminescence , Pcrgamon Press, Oxford, New York (1962) (International Series of Monographs on Semiconductors, vol 5)... 

Scandium iodide added to mercury vapor lamps produces a highly efficient light source resembling sunlight, which is important for indoor or night-time color TV. 

In contrast to spectrophotometry, hght-scattering experiments are generally conducted at constant wavelength. Mercury vapor lamps are the most widely used light sources, since the strong lines at 436 and 546 nm are readily isolated by filters to allow monochromatic illumination. Polarizing filters are also included for both the incident and scattered beams so that depolarization can... 

Concurrent with requirements for low levels of mercurials in discharge water is the problem of their deterrnination. The older methods of wet chemistry are inadequate, and total rehance is placed on instmmental methods. The most popular is atomic absorption spectrophotometry, which rehes on the absorption of light by mercury vapor (4). Solutions of mercury compounds not stabilized with an excess of acid tend to hydrolyze to form yeUow-to-orange basic hydrates. These frequendy absorb onto the walls of containers and may interfere with analytical results when low levels (ppm) of mercury are determined. 

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to >1 MPa (<1 to >10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

EXPLOSION-PROOF LIGHTING FIXTURE INCANDESCENT AND MERCURY VAPOR (FOR EXTERNAL BALLAST)... 

Franck and Gustav Hertz passed electrons through mercury vapor at low pressure to determine the minimum kinetic energy required to produce the excited state that emits ultraviolet light at 253.7 nm. What is that minimum kinetic energy What wavelength is associated with electrons of this energy ... 

For walkways, where 3 foot-candles is an adequate amount of illumination, two 175-watt R-40 mercury vapor lamps placed every 54 ft may be specified. For these and areas that are used continuously but have adequate windows it may be assumed that the lights are on 4,500 hours per year. (This is approximately half the time.) For some interior areas they may never be turned off. At the other extreme, Sarah Lee has an automated warehouse in which the only time lights are needed is when there is an equipment failure. 

To perform the dissociation of the hydrocarbon to alkyl radicals with C—C bond scission, a hydrocarbon molecule should absorb light with the wavelength 270-370 nm. However, alkanes do not absorb light with such wavelength. Therefore, photosensitizers are used for free radical initiation in hydrocarbons. Mercury vapor has been used as a sensitizer for the generation of free radicals in the oxidized hydrocarbon [206-212], Nalbandyan [212-214] was the first to study the photooxidation of methane, ethane, and propane using Hg vapor as photosensitizer. Hydroperoxide was isolated as the product of propane oxidation at room temperature. The quantum yield of hydroperoxide was found to be >2, that is, oxidation occurs with short chains. The following scheme of propane photoxidation was proposed [117] ... 

Fluorescent lamps generate light through a low-pressure mercury vapor discharge that has strong emission tines in the UV, namely at A = 254 nm and around 366 nm. The fluorescent layer is excited by the UV radiation and emits in the visible part of the spectrum. While remains of the 254 nm tine are efficiently rejected by the glass tube, some fraction of the 366 nm radiation can be measured in the emission spectrum of the lamp. 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

Interest in the photochemistry of boron compounds dates back as far as 1913 when Alfred Stock investigated the effects of light from a mercury vapor lamp on diboran 6) and on tetraboran 10). In the case of diborane(6) he commented UV light will also decompose B2H6. The volume of a sample in a quartz tube increased by 1/6 after 24 hours exposure to a mercury-arc lamp, and a pale yellow crystalline substance appeared. Stock also observed that B4H q decomposition to B2H is not noticeably influenced by sunlight. 

Rhodamine is a preferred fluorochrome over fluorescein because of its slower bleach rate and its emission in a spectrum that shows less cellular autofluorescence. Also, this spectrum produces less autofluorescence in plastic substrata (see Chapter 14). Rhodamine requires a mercury vapor light source, since other sources, such as xenon, do not have sufficient emission in the green spectrum. 

Another common use is as a liquid contact in electrical silent switches. Also, mercury-vapor produces the bluish-white light of streedights. However, mercury-vapor hghts now are being replaced by sodium-vapor lights that produce a yellowish-white hght. Mercury is used in thermometers and barometers, to coat mirrors, and in the electronics industry and several other industries. 

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