CA1185311A - Heat lamp having visible radiation blocking coating and method of making - Google Patents

Heat lamp having visible radiation blocking coating and method of making

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Publication number
CA1185311A
CA1185311A CA000414004A CA414004A CA1185311A CA 1185311 A CA1185311 A CA 1185311A CA 000414004 A CA000414004 A CA 000414004A CA 414004 A CA414004 A CA 414004A CA 1185311 A CA1185311 A CA 1185311A
Authority
CA
Canada
Prior art keywords
coating
envelope
heat lamp
lamp
radiation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000414004A
Other languages
French (fr)
Inventor
Mary S. Jaffe
Milan R. Vukcevich
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Application granted granted Critical
Publication of CA1185311A publication Critical patent/CA1185311A/en
Expired legal-status Critical Current

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Abstract

HEAT LAMP HAVING VISIBLE RADIATION
BLOCKING COATING AND METHOD OF MAKING

ABSTRACT OF THE DISCLOSURE
A coating of iron oxide on the outside of a quartz heat lamp absorbs most of the blue and green radiation and provides a deep red color while passing infrared efficiently. The coating may be applied to the com-pleted lamp by operating it and spraying it with ferric chloride solution until the desired coating thickness of iron oxide has been built up.

Description

3~

HEAT LAMP HAVIN5 VISIBLE R~DIATION
BLOCXING COATING AND METHOD OF ~KING

The invention relates to a tubular tungsten filament heat lamp intended for radiant people-heaters which is provided with a visible radiation blocking coating and to a convenient method of making such a lamp.

BACKGROUND OF THE INVENTION
The high cost of fuels and heating has hrought on a trend to lower maintained temperatures in homes and of-fices during cool weather. This has caused a resurgencein popularity of radiant electric heaters for heating people. In radiant heating, heat in the form of infrared radiation travels directly from the source to the object being heated with practically no 10s5 to the intervening air. By directing the radiation at people, they can be made comfortable at room temperatures considerably lower than would otherwise be required for comfort, and in this way radiant people-heaters can be used to reduce heating cos~s .
When radiant heat is used to warm people, it is most effective in a wavelength region in the near infrared, from about 1 to 3 microns. The skin is more opaque to longer wavelengths so that they are less effective in interacting directly with the nerve ends and can only warm a person by increasing the temperature ~, 3~

o~ the surroundings. A tungsten filament lamp operating at about 2800K will emit copiously in the desired wave-lengths, but such a lamp/ in a clear envelope, is un-comfortably bright to the eyes. Also it is unsuitable for use in the dark, as in a bedroom during the night.
Psychologically a reddish orange glow, like a wood fire, is most comforting.

SUMMARY OF THE INVENTION
The object of the invention is to provide a coating for the vitreous envelopes of heat lamps which absorbs most of the blue and green visible radiation but passes infrared efficiently. The coating should be stable, ad-herent, inexpensive and preferably of pleasing appearance when the lamp is not lit.
Another object of the invention is to provide a method for ~pplying such a coating which is readily adaptable to factory procedures and which is inexpensive.
In accordance with our invention, we provide on a radiation-transmitting lamp envelope a coating of iron oxide which has the desired properties of blocking blue and green while ~ransmitting infrared efficiently. The coating may be applied by heating the envelope in air and spraying a solution of ferric chloride on it.
In a preferred method particularly suitable for ap-plying a coating to a tubular quartz heat lamp, the lampis completely made and operated in order to self-heat and raise its envelope to a high temperature~ While hot, the vitreous envelope is sprayed with an alcoholic solution of ferric chloride until a coating of iron oxide having the desired thickness is built up.

DESCRIPTION OF DRAWINGS
FIG. 1 illustrates pictorially apparatus suitable for spraying ferric chloride solution on a tubular heat lamp ~i5~

FIG. 2 is a graph showing the transmission charac-teris-tics of quartz tubiny coated with an iron oxide film according -to the invention.
FIG. 3 is a graph comparing the transmission charac-teristics of ferric oxide film, copper striking color,and cadmium sulfo-selenide film.
FIG. 4 is a graph correla-ting the transmittance of ferric oxide film to the transmissivity of human skin.
DETAILED DESCRIPTION
~ur invention is particularly useful in connection with tubular quartz heat lamps such as described in U.S. patent 3,073,986 to William E. ~lodge, Electric Incandescent Lamp, issued January 1963, the disclosure of which forms a part of the prior art. To provide an iron oxide coating on the lamp envelope, it may be sprayed while hot with a solution of ferric chloride.
Apparatus suitable for practicing the process of our invention is shown in FIG. 1. It comprises a conductive head sleeve 1 supported by an insulating collar 2 journalled in a reduction gear box 3 driven by a fractional horsepower electric motor 4. A cooperating conductive tail sleeve 5 insulated by a collar 6 is free-turning and journalled in a bearing 7. The sleeves accommodate the ends of an elon-gated electric lamp 8 comprising a tubular quartz envelope containing a tungsten filament extending axially from end to end. A spring-loaded bushing 9 in tail sleeve 5 biases the lamp against the head sleeve to prevent movement. Pig tails 10,11 attached to the lamp ends are -threaded -through the sleeves and emerge at 12 and 13 respectively. They are gripped by alligator clips 14,15 attached to the conductive sleeves. The sleeves are engaged by brushing contacts 16,17 through which electric current may be supplied to the lamp to operate it and cause it to self-hea-t while it is slowly revolving.
In spraying solution onto hot quartz subs-trates to make an iron oxide film we have used water and a number of alco-3~

~ LD 8704 hols as solvents. Organic solvents have the advantage of cooling the lamp less as they are sprayed on. Primary al-cohols are preferred because secondary and tertiary alcohols tend to make an insoluble complex which settles out as a sludge and might clog the spray gun orifice. By way of ex-ample, one solution was made up with 6.3 weight~ FeC13 6H20 (ferric chloride hexahydrate) and 0.2% concentrated HCl in denatured ethyl alcohol. Films from ferric chloride dis-solved in water are a little spotty but otherwise build up as well as ethanol films with repeated ~praying.
The solution is conveniently sprayed onto the lamp in a hooded ventilated enclosure using an acid resistant spray head 19 as illustrated in FIG. 1. It comprises a glass bottle reservoir 20 containing the ferric chloride alco-hol solution indicated at 21. A pressure tube 22 is sealedinto the bottle; it has an aperture above the liquid level and encloses a fine bore suction tube 24 which goes down into the liquid. The pressurized nitrogen gas is supplied by flexible tubing 25 to the pressure tube. When the op-erator blocks the relief aperture 26 with his finger, thenitrogen gas pressure is applied above the liquid and also nitrogen gas issues from the spray nozzle 27. The liquid is entrained in the nitrogen jet and a fine spray of FeC13 issues~ With skill in spray painting while the lamp re-volves, a smooth even coating of Fe203 can be obtained.Depending upon the volume or density of the spray, it may be desirable to spray intermittently in order to allow the lamp to recover its temperature. Spraying is con-tinued until the desired thickness of coating has been achieved. For heat lamps, the film thickness may be in the range from 0.05 to 1.0 microns depending on the appli-cation. For the present lamp intended for people warming use, we prefer the range from about 0.1 to 0.4 microns.
~he completed film or coating has a pleasing bronze metal-like appearance; it appears to be primarily ferxic oxide.
The use of our coating for heat lamps provides several 3~

advantages over the prior art. In conventional copper "striking" colors, vitreous material first is coated with a metallic copper salt and then is heated to diffuse the salt into the material. A material increasingly used in the lamp industry as an alternative to vitreous silica is a quartz-like glass known as Vycor ~Corning Glass Works). It begins as a borosilicate glass in which form it can be worked and shaped to normal glassworking tol-erances. An acid leaching process then removes pra~ti-cally ~11 constituents except the silica and a littleboric oxide, leaving the article filled with millions of tiny holes, after which the porous structure is con-solidated by high temperature firing. In a colored form of such material known as red Vycor, the coloration is due to colloidal particles of copper dispersed in the outer layer. A problem in making heat lamps with such material is loss of the red color at the lamp ends and about the exhaust tip. The color is lost when the vitreous material is heated to plasticity for sealing in the inleads or for tipping off the exhaust tube. The vitreous material may become clear near the ends or at the center near the exhaust tube resulting in bright spots which greatly dimimish the utility of the lamp as a radiant people heater. Our process eliminates this problem inasmuch as the iron-oxide coating is formed on an otherwise completely finished lamp which is never thereafter heated hot enough to affect the coa~ing.
Our iron oxide coating is fully stable in air and requires no special care. It may be applied to glass envelopes as well as to fused silica, and is entirely suitable for use with concentrated filament reflector type heat lamps, for instance mold blown so called R-bulb lamps. By contrast cadmium sulfo-selenide is susceptible of attack by acids and must be used on the inside of a lamp; it cannot be applied and used on the outside.

~S3~

A major advantage of our coating is its lesser ab-sorption in the near infrared by comparison with other coatings used for blocking visible light. It is pref-erable that the coating either transmit or reflect, de~
pending upon the wavelength. With a small diameter tubu-lar lamp envelope, reflected radiation can be effectively redirected onto the filament for an improvement in effi-ciency. -But absorbed radiation merely heats the vitreous envelope, and the heat of the envelope is dissipated pri-marily by convection so that it is wasted as far as radi~ant heating is concerned. Our coating is superior to other available coatings such as copper striking colors or cadmium sulfo-selenide which absorbs excessively in the infrared. FIG. 2 shows the percentage transmission, reflection and absorption of quartz or fused silica coated with our Fe203 film. Absorption is nearly 100% at the blue end of the visible spectrum but drops off pre-cipitously towards the red end while transmission rises.
In the infrared beyond 1.3 microns, absorption is less than 10% and the greater part of the radia~ion is trans-mitted while most o what is not transmitted is reflected.
FIG. 3 compares the relative transmission of iron oxide, copper striking color, and cadmium sulfo~selenide film. In the infrared range of interest for heating people, the transmission of iron oxide is highest, rising over 80% at 1~3 microns and staying above the others throughout the range. Ths index of refraction of the Fe203 film is high, being close to 3.
The remarkable suitability and effectiveness of iron oxide film as a filter for a radiant heat lamp is brought out in FIG. 4. When radiation impinges on human skin, part is transmitted through the skin and interacts di-rectly with the nerve ends, producing the sensation of warmth. The solid line curve in FIG. 4 shows the trans-missivity of human skin, that is the extent to which radiation enters it. The two depressions in the curve are due to the absorption bands of water; the inter-national eye sensitivity curve (dotted line) is shown for comparison. It will be observed that the trans-mission curve of the iron oxide film or filter (dot-dash line) rises with the skin transmissivity curve in a close match. At the same time the major part of the visible radiation is cut off, leaving only a small visible "window", shown cross-hatched. Thus the bright-ness is reduced to an acceptable level even for nighttime use, and the deep red color resulting from the trans-mission through the small "window" is pleasant and entire-ly suitable for a heater for warming people.
While the invention has been described with reference to a particular embodiment, such embodiment is intended as an illustrative example. The appended claims are in-tended to cover the modifications which may be made by those skilled in the art without departing from the scope of the invention.

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. An electric heat lamp comprising an envelope of radiation-transmitting material, a source of radiation extending from the visible into the infrared sealed therein, and a coating of iron oxide on said envelope absorbing blue and green visible radiation but passing infrared radiation effective to provide a deep red color transmission during the operation of said electric heat lamp.
2. A heat lamp as in claim 1 wherein said envelope is made of a vitreous material.
3. A heat lamp as in claim 2 wherein said coating is applied to the outside of said envelope.
4. A heat lamp as in claim 3 wherein said coating has a thickness in the range of 0.05 to 1.0 microns.
5. A heat lamp as in claim 1 wherein said envelope has inleads sealed thereinto and said source of radiation is a tungsten filament connected across said inleads.
6. An electric heat lamp comprising an envelope of vitreous material having inleads sealed thereinto, a tungsten filament connected across said inleads and serving in operation as a source of radiation extending from the visible into the infrared, and a coating of iron oxide on the outside of said vitreous envelope resulting from the heat-decomposition in air of a halogen salt of iron, said coating of iron oxide absorbing blue and green visible radiation but passing infrared.
7. A heat lamp as in claim 6 wherein said coating has a thickness in the range of 0.05 to 1.0 microns.
8. A heat lamp as in claim 6 for warming people and wherein said coating has a thickness in the range of 0.1 to 0.4 microns.
9. A heat lamp as in claim 6, said coating being made to contact said vitreous material at high temperature.
10. A heat lamp as in claim 9 wherein said coating results from the heat-decomposition in air of ferric chloride in solution and sprayed onto the vitreous material.
11. The method of making an electric heat lamp having an external coating which absorbs blue and green visible radiation but passes infrared, which comprises:
making a lamp comprising an elongated vitreous envelope having inleads sealed in-to its ends and a resistive filament extending between said inleads, turning on said lamp in order to self-heat it and raise its envelope to a temperature where it will decompose iron halide made to contact it, and while the envelope is at said temperature, directing a fine spray of iron halide in a liquid solvent against it.
12. The method of claim 11 wherein said fine spray is ferric chloride dissolved in a primary alcohol.
13. The method of claim 12 wherein said alcohol is ethanol or 1-propanol.
CA000414004A 1981-11-18 1982-10-22 Heat lamp having visible radiation blocking coating and method of making Expired CA1185311A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US32242181A 1981-11-18 1981-11-18
US322,421 1989-03-10

Publications (1)

Publication Number Publication Date
CA1185311A true CA1185311A (en) 1985-04-09

Family

ID=23254806

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000414004A Expired CA1185311A (en) 1981-11-18 1982-10-22 Heat lamp having visible radiation blocking coating and method of making

Country Status (1)

Country Link
CA (1) CA1185311A (en)

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