US2864966A - Non-actinic fluorescent lamp - Google Patents

Description

Dec. 16, 1958 L. BURNS NON-ACTINIC FLUORESCENT LAMP Filed De c. 2. 1955 ANGSTRQM UNITS 3025 N30 3340 IN VEN TOR! NON-ACTINIC FLUORESCENT LAMP Laurence Burns, Swampscott, Mass, assignor to Sylvania Electric Products Inc, Salem, Mass, a corporation of Massachusetts Application December 2, 1955, Serial No. 551,280

3 Claims. (Cl. 313-109) This invention relates to electric discharge lamps and particularly to fluorescent lamps.

An object of the invention is to reduce eye fatigue and the like from fluorescent lamps by eliminating or reducing the amount of ultra-violet light emitted by such lamps. A feature of the invention is a fluorescent lamp envelope which transmits visible but absorbs ultra-violet light and another feature is a coating for this same purpose. Other objects, advantages and features of the invention will be apparent from the following description taken in connection with the accompanying drawing in which:

Figure l is a representation of a spectrogram of an ordinary fluorescent lamp;

Figure 2 is a lamp according to the invention;

Figure 3 is a fixture according to the invention;

Figure 4 is another fixture according to the invention;

Figure 5 is a broken view in section, of a lamp according to a modification of the invention; and

Figure 6 is a broken view, in section, of a lamp according to further modification of the invention.

It has been found that fluorescent lamps often produce eye fatigue greater than that from incandescent lamps. This may be due to various factors, one of which is the ultra-violet emission from the lamps. The lamps ordinarily produce the mercury spectrum, which includes radiation, or lines as in Figure 1, at roughly 3650 Angstrom units, and also at 3340, 3130 and 3025. These radiations cause the eye itself to fluoresce, and by thus reducing the sharpness of vision under the light, cause eye strain. When the fluorescent materials used are a blend of magnesium tungstate and zinc manganese beryllium silicate, there is very little ultra-violet radiation from the fluorescent powders themselves, but the mercury radiations previously mentioned still are present. When calcium tungstate is used as one of the fluorescent materials, radiations just below the blue are produced and when calcium silicate, activated conjointly with manganese and lead is used, considerable radiation of about 3200 Angstrom units is produced. The latter phosphor produces a bull visible light but also some ultraviolet; it has two separated emission bands.

Figure 2 shows a glass envelope 1, containing an inert gas, for example, argon at a few millimeters pressure, and mercury vapor, and having an electrode 2, 3 sealed into each end by the lead-in wires 4, 5, 6, 7. A fluorescent coating 3 is on the inside of the envelope 1. The envelope 1 has heretofore been made of lead or lime nited States Patent .Zfifiifibb Patented Dec. 16, 1958 ice - to radiations below 3000 Angstrom, such as the 2537 glass which transmits ultraviolet in the region above 3000 Angstrom mercury radiation. Such a material would be Z1110 vanadate or uranium-activated calcium fluoride or sodium fluoride, for example. These give a yellow or yellowish-green light, and the main fluorescent materials used would have to be such, or so blended, as to give a white light, or the desired color, in the presence of this additional light.

In some cases it may be more convenient to us an ultraviolet absorbing glass or plastic in the fixture, as shown schematically in cross-section in Figure 3, where the lamp 10 is surrounded by the reflector 11 and the light transmitting, ultra-violet absorbing piece 12.

In other cases, it may be desirable to use the louvres. 13 as shown in Figure 4. These will shield the eyes from the direct light from the lamp or lamps 10 in the reflector 11, and may have a coating 18 of a substance which reflects'visible light but absorbs ultra-violet. The fluorescent materials previously mentioned may be used for this purpose, eing applied in a varnish, a lacquer, or a plastic. The louvres 13 may be, for example, as shown in application, Serial No. 481,040, filed March 29, 1943, by Rene G. Maurette. When a blend of fluorescent powders including calcium silicate activated with both manganese and lead conjointly is used, it may be desirable to mix in with the blend a green or yellowishgreen fluorescing material, responsive to the ultraviolet emitted by the calcium silicate. This will eliminate or reduce the amount of ultra-violet emitted by the coating-as well as that emitted by the mercury vaporand will at the same time add some green light to that emitted by the calcium silicate. Since the spectrum of calcium silicate, even when supplemented by the spectrum of magnesium tungstate physically admixed with it, is generally slightly deficient in the green, this serves a double purpose.

The uranium-activated calcium fluorides and other materials of U. S. Patent 2,323,284, issued June 29, 1943 to W. P. Toorks may prove useful in this respect. Zinc Vanadate may be useful if the yellow portion of the spectrum is to be enhanced.

The usual lead or lime glass used in fluorescent lamp bulbs decreases rapidly in transmission with wavelength, as the latter is reduced below 3300 Angstroms, so that the wavelengths above this value are the chief ones to be absorbed from the present lamps although some of the lower wavelengths down to 3000 Angstroms are trans mitted to a lesser extent. When the fluorescent material used has high emission below 3300 Angstroms, considerable radiation below that wavelength may be emitted despite the low glass transmission of regular bulbs at that wavelength.

Where an absorbing layer 14, 15 is used in the lamp, it should be ordinarily placed between the regular layer 8 and the glass envelope 1, unless it is placed on the outside of the glass envelope, or unless it has high transmission for the 2500 Angstrom radiation which excites the main fluorescent material. In addition to the absorbing materials previously mentioned, zinc or titanium oxides will be found quite effective, zinc being especially effective against the 3650 Angstrom wavelengths and lower. Zinc oxide will also be found good as a material for the coating 17, 18 on reflector 11 and louvres 13, in

Where the glass transmission is reduced by addition I of ferrous oxide to the batch from which it is made, 0.2 to 1% will generally be found sufiicient. Titanium and cerium oxides have also been found effective for this purpose. 1

In Figures 3 and 4, the filter 12 and louvres 13 are shown in cross-section. They extend longitudinally with the tube 10.

A thin gold film on the .glass envelope may sometimes be desirable as the filter 14, 15 which transmits visible and absorbs ultra-violet light. Such a film has the additional advantage that it allows starting of the lamp at lower voltage and makes its starting independent of the ambient humidity. In ordinary commercial fluorescent lamps as now sold, the necessary starting voltage'rises with humidity.

This rise may also be reduced in a different manner without the gold coating, 'by providing spring metal pieces 16 electrically connected to and extending from the metal reflector 11 ordinarily used with the lamp 10, and bearing on the glass envelope 1 of the lamp 111 near the cathode 3. One may be used at each end of the lamp, but if the reflector 11 is, directly or indirectly, grounded to one end of the lamp, the spring piece bearing on -the glass may be used at only the ungrounded end of the lamp 10. The spring piece 16 will ordinarily bear-on the side of the lamp 10 nearest the reflector 11, to be out of sight and to facilitate insertion of the lamps in its sockets. This spring piece 1'6 may, of course, be used with the present commercial fluorescent lamps, which do not have ultra-violet absorbing means. And conversely, such a spring piece 16 is not at all necessary with my ultra-violet absorbing lamps unless a better starting condition is desired than is usual in present commercial lamps.

This application is in part a continuation of my copending applications Serial No. 568,737, filed December 18, 1954, now U. S. Patent No. 2,799,809, Serial No. 50,608 filed September 22, 1948, now abandoned and Serial No. 206,440, filed January 17, 1951, now U. S. Patent No. 2,714,903.

What I claim is:

l. A fluorescent lighting fixture comprising a metallic reflector, a fluorescent lamp having a tubular envelope of light-transmitting-glass and a fluorescent coating on the inner surface of said envelope, means for holding said lamp in light-reflecting relationship to said reflector and a metal piece electrically and mechanically connected to said reflector and bearing on the outside surface of the tubular envelope of said lamp.

2. The fixture of claim -1, in which the metal piece bears on said envelope near a cathode, to facilitate starting.

3. The fixture of claim 1, in which there is a coating of titanium oxide between the fluorescent coating and the inner surface of said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,112,718 Somers Mar. 29, 1938 2,135,691 Alterthum et al Nov. 8, 1938 2,156,068 Ruttenauer et al Apr. 25, 1939 2,264,092 McCauley Nov. 25, 1941 2,774,903 Burns Dec. 18, 1956

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