US1425967A - Samuel - Google Patents

Description

S. O. HOFFMAN.

LAMP.

APPLICATION FILED Nov. 28,192 I Patented Aug. 15, 1922.

INVENTOR J'AMuEL 0. HQFFMAN.

. B I I x44 ATTORNEYS UNITED STATES PATENT OFFICE.

SAMUEL O. HUFFMAN, OF SAN FRANCISCO, CALIFORNIA.

LAMP.

To all whom it may concern Be it known that I, SAMUEL O. HOFFMAN, a citizen of the United States, and a resident of the city and county of San Francisco, State of California, have invented a new and useful Lamp, of which the following is a specification.

This invention relates to illumination and more particularly to lamps of the type shown in my ber 29, 1911 and No. 1,083,325 and No. 1,083,326, dated January 6, 1914, which consist of an incandescent (source, and means for returning the Infra-red radiation back to the source where it is absorbed, and converted into luminous radiation; the luminous radiation being continually allowed to escape.

In my present application, I accomplish the sparation and backward reflection of the infra-red rays directly, by employing a suitably constructed thin film on the inner surface of the glass globe, no inner tube or globe being necessary. The theory of the action of this film depends upon phenomena known to physicists, manifested as the colors observed in connection with thin films, e. g. the colors of soap bubbles. Briefly, a film oftransparent material, of the order of thickness of a wave length of light, will refuse to transmit light of a certain wave lengthor lengths, and transmit in excess light complementary to this wave length. This is due to the destructive interference between the portions of light reflected from the two surfaces of the thin film. Since the theory of this action is well understood, I will not elaborate it but simply state, the facts as above. These thin films in general selectively reflect only a limited portion of the spectrum.

Previous to my invention it had not been noticed that a film of a certain critical thickness will reflect practically all the wave lengths comprising white light and transmit all Y the infra-red wave lengths; or, vice versa, transmit all the wave lengths comprising white light and reflect all the infrared, which of course constitutes the ideal selective reflector.

vThe actual thickness of this film cannot be stated in units of length, as it varies with the nature of the material constituting the'thin film.

The thickness, however, may be defined in terms of Newtons rings: Taking these as an index, the thickness of the film that may Patent-No. 1,043,008 of Octoergy (depending upon at the preferably Specification of Letters Patent. Patented Aug, 15, 1922 Application med November as, 1921. Serial No. 518,256.

transmitted up to the extreme red, butfor the longer wave lengths an amount of endices of the thin film and its surrounding the refractive inmedium) would be reflected back; that is a thickness equivalent to the white ring would still be a central black spot by transmitted light for the infra-red waves, or a bright spot by reflected light, or stated otherwise, the infra-red waves would be reflected back.

As only a portion of the energy is acted upon by a single film, it would be necessary to use a number of such films which the l l u a radiation traverses in succession, or else usea film with a higher reflecting power than the ordinary transparent film. Such a special film can be easily constructed by dcpositing by suitable means 'a thin layer of some substance such as stibnite. on each surface of the film, (which in general would consist of such a substance as collodion or cellulose acetate) or even using a thin film of stibnite. I mention stibnite because it is typical of a number of highly reflecting substances, such as the metallic sulphides which same time are transparent, more or less. The final result of any of the above arrangements is that substantially all the light escapes freely. and substantially all the infra-red radiation is returned to the source. 7

Of course the thickness corresponding to any white ring can be used; for example with a white central spot, there is a white ring in the second order. Also lightof a particular color, and even mono-chromatic light can be obtained by a suitable thickness of the thin films.

In practice, the source of radiationis concentrated as nearly as possible in the center of a spherical globe, on the innersurface of which is placed the thin films;

The drawing graphically shows on an enormously enlarged and exaggerated scale, an electric lamp embodying the invention, in which A represents a lamp globe which is preferably spherical, and on the inner surface of which is applied the series of coatingsB, constituting'the selective reflector. is the source of radiation of Waves of various length. On the inner coating-B, 1

represents a transparent material, such as collodion or cellulose acetate, etc., and 2--2 represents layers of a highly reflecting transparent substance, such as stlbnite. Only one of these combination films is shown, but a number are usually used. The idea briefly is to have alternate layers of transparent substances, differing in refractive indices so as to secure a reflection at the boundary.

I claim:

1. A lamp embodying a source of radiation of Waves of various lengths, with a selective reflector around the source embodying a plurality of films and a thin intermediate film of the critical thickness corresponding to the first white ring of Newtons rings, whereby only waves of desired lengths escape and waves of other lengths are reflected back to the source to be absorbed and converted into waves of a length which will not be returned by the reflector.

2. A lamp embodying an incandescent source of radiation of waves of various lengths, a selective reflector around the same embodying a refractive body, the thickness of which is in conformity with the laws governing the interference colors of thin films, such that it allows waves of the desired length to escape freely but reflects the waves of other lengths back to the source where they are converted into waves of a length which will be permitted to escape from the lamp.

3. The combination with a source of incandescent radiation, of a selective reflector around the same, consisting of alternate layers of transparent substances of differing refractive indices, each alternate layer being of the critical thickness corresponding to the first white ring of Newtons rings.

4. In a lamp, the combination of an incandescent source and a selective reflector around the same, said reflector consisting of a thin transparent film on each side of which is deposited a layer of a highly reflecting substance.

In testimony whereof, I have hereunto set my hand.

SAMUEL O. HOFFMAN.

Images