US 3662208 A
In a reflector type incandescent lamp having a concave reflector and a front glass, an electroconductive coating of transparent metal oxides is applied on the inner surface of the front glass and the thickness of the coating is set to manifest a percentage of interception of infrared rays of 20 to 80 percent of that of glass for input powers of less than 0.55 W per cubic centimeter of the volume of the lamp.
Description (OCR text may contain errors)
Q Unlted States Patent [151 3,662,208
Ohmae et a1. 5] May 9, 1972 541 REFLECTOR TYPE INCANDESCENT 3,221,198 11/1965 Van der Waal ..313/112 LAMPS 3,400,288 9/1968 Groth ..313/1 12  Inventors Ken-ii ohmae Tomiyoshi Him 0 both of 3,188,513 6/1965 Hansler ..313/ 1 l2 yokohamafihi; Takao Akaishi, Kim 3,209,188 9/1965 Freeman ..313/43 yushu a! of Japan Primary Evaminer-Herman Karl Saalbach  Assignee: Tokyo Shihaura Electric Co., Ltd., Assist/1m E i -Q Baraff Kawasakl'sh" Japan Attorney-F1ynn and Frishauf  Filed: Jan. 27, 1970  ABSTRACT  App1.No.: 6,204
In a reflector type incandescent lamp having a concave reflector and a front glass, an electroconductive coating of trans-  US. Cl ..3l3/112, 313/1 11, 3 1331/5? parent metal oxides is pp on the inner Surface of the from 51 Im. c1. ..11011 5/16, HOli 61/40, HOlk 1/32 g'ass and "T hicknFss P is manifes a 581 Field Of Search ..313/1 12, 1 17, 108-1 10, mage 'F rays Perm" 9 313/43 25 88/106 that of glass for 1nput powers of less than 0.55 W per cub1c centimeter of the volume of the lamp.
56 R i t I l e erences Cl ed 5 Claims, 6 Drawing Figures UNITED STATES PATENTS 2,795,722 6/1957 Burgener et a1. ..313/117 PATENTEUMAY 9I972 3,662,208
SHEET 1 OF 3 PATENTE111111 9 1912 i1, 662 208 FIG.2
WAVELENGTH (nm) PERCENTAGES F TRANSMISSIBIL AND REFLECTI PERCENTAGE OF INTERCEPTIONPA) RESISTIVITY OF THE COATING (OHM PER SQUARE) PATENTEDHAY. 9 m2 SHEET 3 [1F 3 FIGS 6.2 03 POWER INPUT PER um E S R E Du U m w 0 E O W 3 E T m m O. O. 0 w w 4 2 wtzofinmumfiz VOLUME OF THE ENVELOPE BACKGROUND OF THE INVENTION This invention relates to incandescent lamps, and more particularly to reflector type incandescent lamps having envelopes not transmissible to infrared rays.
In a conventional reflector type incandescent lamp most of the radiant energy emitted from a filament is radiated to the front of the lamp through a front glass covering the opening of the reflector. However, the radiant energy of the filament is much more in the region of infrared rays than in the region of visible light rays of the spectral energy distribution. Consequently, where a high degree of illumination is required as in heater illumination and photographing studios, the radiant energy in the infrared region becomes high thus rendering it uncomfortable for the persons illuminated. Further, as incandescent lamps generally have excellent coloring they are employed to illuminate raw food-stuffs such as fruits, vegetables, fishes or meats. In such applications too, infrared ray energy heats these food-stuffs causing them to degrade, decompose or change color.
In order to solve this problem it has been the practice to make the envelope of glass that absorb infrared rays, or to vacuum deposit on the internal surface of the envelope a substance capable of absorbing infrared rays such as a semiconductor substance.
However, an envelope made of infrared ray absorbent glass also absorbs visible light rays, thus lowering illumination. In addition such a glass is expensive. It is usually necessary to apply more than two layers of the infrared ray absorbent coatings on the inner surface of the envelope thus resulting in the complication of the manufacturing steps, the lowering of the production efficiency and in the increase in the cost of manufacturing.
It is therefore an object of this invention to provide simple and inexpensive reflector type incandescent lamps having a low percentage of infrared ray radiant energy with respect to visible rays.
SUMMARY OF THE INVENTION According to this invention, this object can be accomplished by applying an electroconductive coating of transparent metal oxides on at least the inner surface, and preferably on both surfaces, of the transmissive front glass of the envelope and by setting the thickness of the coating of the transparent metal oxides to have a percentage of interception of infrared rays of to 80 percent of that of a glass plate capable of perfectly intercepting the transmission of the infrared ray radiant energy emanated from a filament where the input power W per unit volume of the envelope is 0.55 W/cc. The terms intercepting and reflecting are used interchangeably herein to describe the properties of the electroconductive coating of transparent metal oxides on the front glass of the envelope. 0.55 W/cc.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side elevation, partly in section, of a reflector type incandescent lamp embodying this invention;
FIG. 2 shows characteristic curves showing the relationship between wavelength of the radiant energy and the percentages of transmissibility and reflection of an electroconductive coating of the transparent metal oxides employed in this invention;
FIG. 3 shows characteristic curves showing the relationship between the thickness and the percentage of interception of visible light and infrared rays of the electroconductive coating of the transparent metal oxides, the percentage of interception being based on that of a conventional lamp without utilizing the electroconductive coating of the invention;
FIG. 4 is a plot of a characteristic curve comparing the maximum temperature rise characteristic against the percentage of infrared ray intercepting characteristic of the reflector type incandescent lamp of the invention and A conventional lamp;
FIG. 5 shows characteristic curves showing the relationship between the power input W per unit volume of the envelope and the percentage of the infrared ray interception of the electroconductive coating of the reflector type incandescent lamp of the invention, taking the temperature of the envelope of the lamp as the parameter; and
FIG. 6 shows a side elevation, partly in section, of another embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 of the accompanying drawings there is shown an embodiment of this invention comprising a glass envelope 1 including a concave reflector member 2 and a front glass plate 3. Preferably, the concave reflector member 2 is shaped in the form of a paraboloid and the front glass 3 is in the form of a lens, although a plate glass 3 is shown. A reflecting coating of metal 4, for example of aluminum, is formed by well known vapor deposition techniques on the inner surface of the concave reflector member 2, and a light source 5 is located at a desired position, preferably at the focus of the paraboloid in a manner well known in the art. Although, in this embodiment, the coating 3 is deposited on the inner surface of the member 2, said electroconductive coating may generally be deposited on at least one surface of the plate glass 3, and preferably be deposited on both surfaces thereof.
The light source 5 comprises a filament 6 supported by a pair of lead wires 7 which extend through suitable openings (not shown) at the bottom of concave reflector member 2 and are respectively soldered to two metal ferrules (not shown) made of a nickel-iron alloy and hermetically sealed to said openings. One of the lead wires 7 is soldered to an eyelet 9 of a base 8 mounted on the bottom of the concave reflector body 2 to cover the ferrules while the other lead wire 7 is soldered to a shell 10 of the base 8.
The entire inner surface of front glass plate 3 closing the opening of the concave reflector member 2 is coated by an electroconductive coating of transparent metal oxides 11 which can be prepared by a conventional method comprising the steps of dispersing a powder of tin oxide (Sn0 antimony oxide sb,o, or indium oxide or a mixture thereof in a solution of a halogenated metal, for instance, a solution of thin chloride, spraying the mixture onto the inner surface of the glass plate 3, heating the coating for, for example, several tens of seconds at a temperature of about 500 C and firing it to remove strain.
After sealing by fusion the front glass plate 3 formed with an electroconductive coating of transparent metal oxides 11 to the opening of the concave reflector member 2, the interior of the assembly is evacuated through an evacuating pipe (not shown), filled with a suitable gas, and the evacuating pipe is tipped off. Thereafter the base 8 is secured to the reflector member 2, thus completing a reflector type incandescent lamp.
FIG. 2 shows the relationship between the wavelength (in nm) of the radiant energy and the percentage of transmission D and the percentage of reflection R of a lamp of this invention where the thickness of the electroconductive coating of the transparent metal oxides l1 equals 0.32 As can be noted from FIG. 2, the coating of the transparent metal oxides 11 transmits visible rays of less than about 800 nm but effectively intercepts the transmission of infrared rays having a wavelength longer than 800 nm by reflecting the infrared rays. It will be readily understood that the transmissibility of the coating of the transparent metal oxides l1 varies dependent upon the thickness of the coating, and that the thickness thereof is related to the resistivity (ohm per square) of the coating. FIG. 3 shows the relationship between the resistivity and the percentage of interception (i.e., reflection) for a distance of 3 meters between the lamp and a surface illuminated thereby. As the thickness of the coating increases, or as the film resistivity decreases, percentages of interception or reflection of visible rays and infrared rays increase. However,
visible rays are not so severely intercepted as infrared rays so that by setting the thickness of the coating 11 to an appropriate value it will be possible to provide effective inter ception of only infrared rays.
if the thickness of the coating is excessively large to perfectly intercept infrared rays, the temperature of the envelope will be increased greatly due to absorbed infrared rays thus resulting in the degradation of the characteristicsof the lamp and decrease in the operating life. For this reason, it is necessary to limit the thickness of the coating 11 in a certain range described hereinafter.
FIG. 4 shows a temperature rise characteristic of a lamp which shows that the ratio of temperature rise amounts to 147 percent at an input power of 0.55 W per unit volume (c.c.) of the envelope 1 and at a percentage of interruption of more than 80 percent and that the temperature reaches 340 C when the lamp illuminates upwardly, thus shortening the operating life. in an extreme case, the lamp may explode. For this reason, it is necessary to set the upper limit of the percentage of interception at most to 80 percent. FIG. 3 shows that the resistivity of the coating equals 15 ohms per square at a percentage of interception of 80 percent.
On the other hand, for lamps of small outputs the thickness of the electroconductive coating of the transparent metal oxides l 1 may be thin but where the resistivity is higher than 100 ohms per square the novel effect of this invention can not be realized. More specifically, lamps wherein the percentage of interception of infrared rays is less than percent, the difference between the percentages of interception of visible rays and of infrared rays becomes too small to be practical.
From the foregoing description, it will be clear that in lamps having an input power W of 0.55 W per cubic centimeter of the volume of the envelope by limiting the percentage of interception of infrared rays in a range of from 20 to 80 percent, it is possible to limit the maximum temperature rise to a value below about 300 C as shown in FIG. 5, thus providing reflector type incandescent lamps of improved characteristics permitting lesser quantity of infrared rays to be radiated. The characteristics shown in FlG. 5 were measured on an envelope having a volume of 370 c.c.
Lamps within the percentage of interception of infrared rays thereof has been limited to 20 to 80 percent, are suitable for decreasing the size of the envelope with respect to the output thus projecting concentrated light beams on small areas, whereas lamps having a power input W of 0.20 W/cc of the volume of the envelope have especially excellent infrared ray interception characteristics.
When a lamp as shown in FIG. 1 is constructed to have a lens 3 the diameter of which is PAR 38 121 mm), an input of 0.27 W/cc of the volume of the envelope for a voltage and a power of l00 V and 100 W, and a resistivity of the coating 11 of 25 ohms per square, then the lamp will have a percentage of interception of infrared rays of 5 8 percent and a percentage of transmission of visible rays of 85 percent. The maximum temperature rise under these conditions is about 250 C which is a practical value. In this embodiment, it is obtained a practical advantage by setting the input of the lamps in the range of 0.20 to 0.45 W/cc and the percentage of the interception of infrared rays in the range of 35 to 65 percent.
While in the embodiment shown in HO. 1, the concave reflector member 2 is shown as being made of glass, a concave reflector 20 is made of metal in a modified embodiment shown in FIG. 6. in this case the vapor deposition of aluminum is, of course, not necessary. Other portions of FIG. 6 corresponding to those of FIG. 1 are designated by the same reference numerals.
What is claimed is:
1. In a reflector type incandescent lamp comprising an envelope including a concave reflector and a light transmissive front glass secured to the opening of said reflector and a source of light disposed in said reflector, the improvement which comprises an electroconductive single layer coating of transparent metal oxides on the inner surface of said front glass, said metal oxides including at least one oxrde selected from the group consisting of tin oxide, antimony oxide, and indium oxide the thickness of said coating being set such that the percentage of reflection of the infrared rays emanated from said light source amounts to 20 to percent of that of glass where the input power is between 0.20 W and 0.55 W per cubic centimeter of the volume of said envelope, to limit the temperature of said envelope to a maximum of approximately 300 C.
2. The lamp as claimed in claim I wherein said concave reflector comprises a paraboloid of glass and a coating of aluminum vapor deposited on the inner surface thereof and wherein said light source is located at the focus of said paraboloid.
3. The lamp as claimed in claim 1 wherein said concave reflector is a metal body having a reflector surface on its inside.
4. The lamp as claimed in claim 1 wherein said front glass is in the form of a lens.
5. The lamp as claimed in claim 1 wherein said lamp has an input power W per unit volume c.c. of said envelope of from 0.20 to 0.45 W/c.c. and a percentage of reflection of infrared rays of from 35 to 65 percent.