US2433404A - Light generating device - Google Patents

Description

Dec. 36, 47. I c. G.' SMITH v 2,433,404

LIGHT GENERATING DEVICE Filed Feb. 25, 1942 Patented Dec. 30, 1947 LIGHT GENERATING DEVICE Charles G. Smith, Medford, Mass.,

Raytheon Manufacturing Company,

assignor to Newton,

Mass., a corporation of Delaware application February 25, 1942, serial No. 432,215

This invention relates to devices for generating radiations. More particularly this invention relates to light generating devices employing a medium, such as for example a iluorescent material, for translating light of certain wave lengths into light of other wave lengths.

Throughout this specification and the claims,`

the following terms are used in the sense herein.. after indicated, except where the text indicates otherwise. The term "light" refers to light radiations both visible and invisible. The term translating in reference to light means changing light of one wave length to Vlight of another wave length. A iiuorescent material is a material which translates light. A transparent material is a material which transmits light without translation.

In light generating devices of the type referred to herein, light of one wave length may be translated by means of asuitable translating material into light of a desired Wave length. For example, in mercury vapor lamps the ultra-violet light which is generated is translated by fluorescent material into visible light. In order to produce translation of most of the ultra-violet light generated, the iiuorescent coating is preferably made of substantial thickness. However, the thicker the uorescent coating is made the more opaque it will be to visible light and will thus absorb the visible lightl that is produced. Ii the iiuorescent coating ismade thinner, however, a substantial portion of the ultra-violet light generated will pass therethrough without translation and will thus be Wasted. However this light might be used to advantage if it could be suitably controlled and directed.

Therefore it is an object of this invention to provide means for controlling and directing radiation emanating from a radiation-generating device.

A further object of this invention is the provision of a light generating device in which a of the light generated is transgreater portion lated with minimum light.

Another object of this invention is the provision of an improved and more efficient light generating device of the type referred to herein.

Other and further objects and advantages of this invention will become apparent and the foregoing objects will be best understood from the following description of embodiments exemplify.- ing said invention, referencebeing had to the accompanying drawing, in which Fig. l is a cross-sectional view of a fluorescent absorption of the translated 2 Claims. (Cl. 176-122) lamp made in accordance with the present invention; and

Fig. 2 is a cross-sectional view of a modified form of a. iiuorescent lamp made in accordance with the present invention.

Referring now specifically to Fig. l, the fluorescent lamp l has an envelope 2 provided with oppositely disposed electrodes 3 which as shown are of the coiled filament type and are preferably coated with an electron emitting material such as barium or strontium oxide, or the like, thereby giving a copious flow of electrons when heated. The electrodes may be made of tungsten or any other suitable material.

Lead-in and supporting conductors for the electrodes 3 extend through press stems li at opposite ends of the envelope 2 and are connected to contact terminals 5 provided at each end of the lamp.

A fluorescent coating 6 of any suitable material, such as the phosphors, is provided on the interior surface of the envelope 2 which is excited by the ultra-violet radiations generated during the discharge and which serves to translate the ultraviolet light nto visible light, which visible light is transmitted through the walls of the envelope.

Prior to sealing oi the lamp a suitable gas 'L' such as argon, neon, or other noble monatomic gases, at several millimeters of pressure is introduced into the envelope together with an ionizabie vapor such as that supplied by a small quantity of mercury 8.

The electrodes 3 are adapted to be heated by a suitable current and upon application of a suitable potential between said electrodes a discharge occurs therebetween. The discharge vaporizes the murcury within an extremely short period of time and causes .the mercury to generate light in which the resonant lines of mercury which lie within the spectral range of about 2537 Angstrom units will predominate.

In this embodiment, in order to produce maximum radiation of the mercury resonance line of about 2537 Angstrom units wave length it is preferred that the temperature of the coolest portion of the lamp be such as to result in a mercury vapor pressurepof the order of 1 to 20 microns, preferably about l0 microns, Within the envelope. It is of course-to be understood that this pressure may be varied within comparatively wide limits and that the lamp will still operate to generate light radiations.

The light generated within the lamp passes through the iiuorescent coating. In this embodiment the fluorescent coating is preferably made thin enough to permit a substantial portion of the translated light. that is the visible light. to pass through said coating without absorption thereof. Furthermore in this embodiment at least a portion of the light generated within the lamp, especially the ultra-violet light, will pass through the fluorescent coating without translation. The portion of the envelope adjacent the coating or on which the coating is arranged is preferably' thin enough and of a material to permit passage therethrough of a substantial portion of the untranslated light. especially at the 2537 Angstrom line, as well as the visible rays.

A jacket 8 including an outer wall I Il spaced from the wall of the envelope is preferably arranged surrounding the uorescent coating. A globule of mercury I I is inserted within the jacket and is adapted to be heated and vaporized by the heat from the envelope. The jacket 9 is closed to enclose this atmosphere of mercury. It is preferred'that the temperature of the jacket be such that the mercury vapor pressure therein is of the order of 100 microns. Of course it is to be understood that this pressure can be varied substantially, as will be apparent hereinafter.

Ordinarily in a container the mercury vapor pressure is determined by the coolest portion of the interior surface thereof. As stated hereinbefore the mercury vapor pressure in the envelope is preferably of the order of l to 20, preferably 10, microns, while that in the jacket is considerably higher. Since both the interior of the envelope and the interior of the jacket are heated directly or indirectly by the energy of the discharge, they would tend tofhave approximately the same temperatures and same pressures. In order, therefore, to provide for a lower pressure in the envelope, a portion thereof may be cooled to a lower temperature to vthereby produce a. lower pressure. I prefer to accomplish this by providing oppositely-disposed extended ends I2 on the envelope. area, these ends tend to be cooler. Furthermore, I prefer to isolate a region I3 within these ends I2 from the rest of the envelope by arranging a pair of relatively thinrperforated washers Il over the interior ends of the stems 4. Each of these washers is held in place by any suitable means. The washers I4 are preferably made of polished aluminum, and therefore 'reilect radiation from the discharge. The perforations I5 in the washers are sufllciently large to permit the vapor to pass freelyltherethrough Without, however, allowing excessive radiation of energy through said perforations. These washers act as excellent heat shields. It will thus be seen that the region I3 will be cooler than the rest of the envelope, and thus produce a pressure less than the pressure Being remote from the discharge within the jacket which is closer to, and not as well insulated from, the heat of the discharge.

If desired another gas i6, such as for instance helium, neon, and argon, may be inserted in the jacket. The gas selected must be one that does not quench the untranslated light, particularly the 2537 Angstrom units line. This gas will serve to conduct heat from the wall of the envelope to the outer wall of the `iacket.

The thickness of the atmosphere in the jacket is preferably such that it is of the order of ten times the mean free path of a photon of light in said atmosphere. If the pressure in the jacket is high enough and the of the untranslated light passing through the iluorescent coating 6 will be reflected back to said coating until said light is translated thereby.

jacket is thick enough most The mercuryatmosphere in the Jacket is substantiallytransparent to the translated light passing from said coating.

It will thus be seen that by providing a thin coat- The visible light will pass therethrough and will serve as a luminant.

A modified embodiment of the present invention is shown in Fig. 2. This embodiment is similar to that shown in Fig. 1,/ except that the uorescent coating 6 is rep aced by a fluorescent coating I 'l which is arranged on the outside of the the wall of the envelope and may be readily made by any one skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is: Y

1. A gaseous electric discharge lamp compris-v ing an envelope, means for producing an electrical discharge in said envelope, mercury vapor at a relatively low pressure in the path of said discharge for generating ylight radiations under the influence thereof, means for translating at least some of said light radiations into light radiations of another wave length, said envelope and said translating means being at least partially transparent to said first-named light radiations, and an atmosphere of mercury vapor at a relatively high pressure surrounding said envelope for refleeting substantially all of the untranslated light radiations passing through said envelope and said translating means back to the translating means.

2. A gaseous electric discharge lamp comprising an envelope, means for producing an electrical discharge in said envelope, mercury vapor at a pressure of the order of one to twenty mi crons in the path of said discharge forgeneratf ing invisible light radiations under the influence thereof, a iuorescent material disposed in the path of said invisible light radiations and adapted to translate at least a portion thereof into visible light radiations, said envelope. and said 6 uorescent material being at least partially transparent to said invisible light radiations, and an atmosphere of mercury vapor at a pressure of labout one hundred microns surrounding said.

envelope for reflecting substantially all of the invisible light radiations passing through said lenvelope and said uorescent material back to said fluorescent material.

CHARLES G. SMITH.

REFERENCES CITED The following references are of record in the le of this patent:

Great Britain Apr. 3, 1936

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