US 2452518 A
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Oct. 26, 1948. L, BURNS 2,452,518
' Nomcwmlc FLuonEscNT LAMP Filed Dec. 18,'1944 nnnon Ums 3025 SISO' 3340 3650 40 O j n 7000 Patented Octq 26, 1948 UNITED STATES PATENT OFFICE NONACTINIC FLUORESCENT LAMP Laurence Burns, Swampscott, Mass., assignor to Sylvania Electric Products Inc.. Salem. Mass., a corporation of Massachusetts Application December 18, 1944, Serial No. 568.737
2 Claims. l
This invention relates to electric discharge Figure 1 is a representation of a spectrogram of an ordinary iiuorescent lamp;
Figure 2 is a lamp according to the invention;
Figure 3 is a fixture according to the invention and Figure 4 is another fixture according to the lnvention.
Figure 5 is a broken view, in section, of a lamp according to a modification of the invention.
Figure 6 ls 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 ultraviolet 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 tluoresce, 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 zine manganese beryllium silicate, there is very litt-le ultraviolet 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 Ang- 'strom units is produced. The latter phosphor produces a buff visible light but also some ultraviolet; it has two separated emission bands.
Figure 2 shows a glass envelope I, 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 leadin wires Il, 5, 6, l.. A fluorescent coating 8 is on the inside of the envelope I. The envelope I has 2 heretofore been made of lead or lime glass which transmits ultraviolet in the region above 3000 Angstrom units to some extent, transmitting 3650 Angstroms very well.
According to my invention, the absorption of this glass f or ultraviolet may be increased by use of additional iron, for example, ferrous oxide, in the glass or by use of an envelope of the glass now well-known asl Noviol, made by the Corning Glass Works, of Corning, N. Y. Novicl 0" is good.
Ifl desired, the glass of the envelope I may remain unchanged, if an ultraviolet absorbing layer I4, I5 is used on the inside or outside of the glass.
A fluorescent material emitting visible light in response to excitation by ultraviolet in the 3000 to 3800 Angstrom range may constitute this layer I4, I5. This would be in addition to the main fluorescent material which responds chiefly to radlations below 3000 Angstrom, such as the 2537 Angstrom mercury radiation. Such a material would be vzinc vanadate or uranium-activated calciuml 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 use an ultraviolet vabsorbing glass or plastic in the fixture, as shown schematically in cross-section in Figure 3, where the lamp I0 is surrounded by the reflector Il andthe light transmitting, ultraviolet absorbing piece I2.
In other cases, it may be desirable to use the louvres I3 as shown in Figure 4. These will shield the eyes from the direct light from the lamp or lamps I 0 in the reflector I I, and may have a coating I8 of a substance which reflects visible light but absorbs ultraviolet. The uorescent materials previously mentioned may be used -for this purpose` being applied in a varnish, a lacquer, or a plastic. The louvres I3 may be, for example, as shown in application, Serial No. 481,040, filed March 29, 1943. by Rene G. Maurette, which issued on December 12, 1944, as U, S, Patent No. 2.364.992.
When a blend of uorescent 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 uorescing material, responsive to the ultraviolet emitted by the calcium silicate. This will eliminate or reduce the amount of ultraviolet emitted by the coating-as well as that emitted by the mercury vapor-and will at the sametime 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 transmitted to a lesser extent. When the iluorescent 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 I4, I is used in the lamp, it should be ordinarily .placedbetween the regular uorescent layer 8 and the glass envelope I, 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 iiuorescent 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 coating reilector II and louvres I3 in Figure 2, for it dees not reiiect ultraviolet light but does reilect visible light.
Titanium is also useful in this respect, but is not as effective in preventing reiiection as it is in preventing transmission. Lithopone is effective against transmission, but not against reection.
= Crookes glass, particularly that known as Crookes A, reduces the 3650 radiation to a small 'I'his rise may also be reduced in a different manner without the gold coating, by providing spring metal pieces I6 electrically connected to and extending from the metal reiiector II ordinarily/used with the lamp I0, and bearing on the glass envelope I of the lamp III near the cathode 3. One may be used at each end of the lamp, but if the reiiector II is, .directly or indirectly, Jgrounded to loneend of' thelampl,vthe spring piece bearing on the glass may be used at only the ungrounded end of the lamp I0. The spring piece `I6 will ordinarily bear on the side of the lamp I0 nearest the reector II, to be out of sight and to facilitate insertion of the lamps in its sockets.
This spring piece I6 may, of course, -be used with the present commercial nuorescent lamps, which percentage, and substantially eliminates thosey lower, in a thickness of 2 millimeters. It is thus very effective as a lter glass I2 in the fixture of Figure 2, and is also effective as the glass'of thelamp envelope.
Where the glass transmission is reduced by addition of ferrous oxide to the batch from which it is made, 0.2 to 1% will generally =be found suincient. Titanium and cerium oxides have also been found effective for this purpose.
In Figures 3 and 4, the lter I2 and louvres I3 are shown in cross-section. They extend longitudinally with the tube I0.
A thin gold nlm on the glass envelope may sometimes lbe desirable as the filter Il, I5 which transmits visible and absorbs ultraviolet 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.
do not have ultraviolet absorbing means. And conversely, such a spring piece I6 is not at all necessary with my ultraviolet absorbing lamps unless a better starting condition is desired than is usual in present commercial lamps.
vAnother application, Serial'No. 50,608, based on the present application, was led September 22, 1948.
What I claim is: 1. A uorescent coating for excitation by a mercury discharge producing 2537 Angstrom unitsl radiation, comprising a combination of the following phosphors in physical contact: calcium silicate, activated conjointly with manganese and lead and emitting visible radiation and also ultraviolet in response to mercury excitation, and one of the phosphors in the following group responding to the ultraviolet emitted by said calcium silicate: uranium-activated calcium fluoride and zinc vanadate.
2. A uorescent coating for excitation by a mercury discharge producing 2537 Angstrom units radiation, comprising a combination of the following phosphors in physical contact: calcium silicate activated conjointly with manganese and lead and emitting ultraviolet radiation and visible radiation deficient in the green in response to said mercury excitation, and uranium-activated calcium fluoride emitting green radiation in response to the ultraviolet emitted by said calcium silicate.
REFERENCES CITED The following references are of record in thev iile of this patent:
UNITED STATES PATENTS Number Name Date 2,061,892 Burns Nov. 24, 1936 2,269,819 Isenberg Jan. 13, 1942 2,272,992 Hebo Feb. 10, 1942 2,296,643 Leverenz Sept. 22, 1942 2,298,947 Leverenz Oct. 13, 1942 2,314.096 Leverenz Mar. 16, 1943 2 316,366 Ruttenauer Apr. 13, 1943 2,324,384 Grimes July 13, 1943 2,346,522 Gessel Apr. 11, 1944 2,347,671 Dircksen May 2, 1944