1. Field of the Invention
This invention relates generally to halogen infrared lamps with reflective coatings on the lamp envelope. More particularly, this invention relates to halogen infrared lamps coated with an infrared reflective coating substantially surrounding the entire envelope along with a totally reflecting coating disposed on ends of an ellipsoidal portion of the envelope.
2. Discussion of the Art
Improving the efficiency of lamps is increasingly important due to the rising cost of energy. Infrared reflective filters, a form of interference filters, have been used to improve the energy efficiency of lamps by reflecting infrared radiation towards the filament to heat the filament and thus increase the efficacy of the lamp. Interference filters have also been used to selectively reflect or transmit light radiation from certain portions of the electromagnetic radiation spectrum such as ultraviolet, visible, and infrared radiation. Interference filters have been used to allow a portion of the visible radiation to transmit through the envelope and reflecting the unwanted visible radiation to produce colored light.
A halogen infrared (HIR) lamp uses an infrared (IR) reflective coating on an elliptical surface of a double ended quartz halogen lamp to preferentially reflect IR radiation to a filament. This coating, however, allows some IR radiation to pass since the reflectivity in the IR region is not one hundred percent. Metal halide discharge lamps have used reflective end-coats to improve the efficacy of lamps by heating up the ends where a metal halide pool forms, thereby increasing the vapor pressure of the pool and therefore the efficacy. Moreover, computer modeling has uncovered that in HIR lamps, IR radiation is preferentially lost at particular angles as measured from the radial axis formed along the filament. If an HIR lamp recaptures the IR radiation lost at these particular angles by using an additional reflective end-coating, similar to metal halide discharge lamps, it is believed that the efficacy of the lamp can be improved.
The present invention is directed to a totally reflecting coating placed near the ends of a HIR lamp to reflect visible and IR radiation at low acute angles and large obtuse angles as measured from an axis defined along the filament. The totally reflecting coating reflects visible and IR radiation towards the filament to heat the filament. Due to the fact that more IR radiation is lost at these angles compared to visible light, the net effect is to return more IR radiation to the coil, thereby heating the coil and increasing the efficacy of the lamp.
The light source is comprised of a light transmissive lamp envelope having a filament centrally disposed within the envelope. The envelope described above has an ellipsoidal portion located centrally between two tubular portions disposed on opposite ends of the ellipsoidal portion. An IR reflective coating substantially surrounds the entire ellipsoidal portion of the envelope and a totally reflecting coating is located on ends of the envelope.
A pair of lead wires are connected to opposite ends of the filament. In another embodiment, the light source may have lead wires extending from only one end of the lamp.
One exemplary embodiment of the lamp has an IR reflective filter coating containing alternate layers of materials with different refractive indices. These different refractive indices allow desired radiation through while reflecting the unwanted radiation. The present invention advantageously provides a totally reflecting coating near the ends of the HIR lamp to preferentially reflect the IR radiation that usually would escape and direct it towards the filament.
The totally reflecting coating on both ends of the envelope preferably subtends an angle from approximately 22° to approximately 45° from the filament axis and surrounding the entire envelope.
A primary benefit of the invention resides in the increased efficacy associated with the subject lamp.
Another benefit of the invention relates to the simple manner in which efficacy of the lamp can be improved.
Exemplary embodiments of the invention are shown in
The filament 104 extends longitudinally along a major axis of the ellipsoidal portion of the envelope 102. In the preferred embodiment, the filament 104 is a tungsten material and is a coiled-coil type filament, although other filament material and configurations are not outside the scope of the present invention. First and second seals 114, 116 are provided at opposite ends of the envelope 102 in a manner that is well known in the art.
An IR reflective film 118 is provided on the outer surface of the envelope 102. In the preferred embodiment, the IR reflective film 118 is deposited on the envelope 102 by vapor deposition or sputtering; however, the IR film 118 may be deposited on the envelope 102 by other methods. The IR reflective film 118 acts in concert with the ellipsoidal shape of the envelope 102 and the placement of the filament 104 along the major axis A of the ellipsoidal portion of the envelope 102 to perform multiple functions. First, the IR film 118 reflects IR radiation emitted by the lamp towards the filament 104 in order to increase the efficacy of the light source 100. Second, the IR film 118 allows other portions of the radiated spectrum, including visible radiation emitted by the filament 104, to pass through the envelope 102.
It is desired, though not necessary, that the IR film 118 have the optical and temperature properties similar to the filter disclosed in U.S. Pat. No. 4,229,006. The IR film 118 of the exemplary embodiment is a composite or a plurality of stacked layers comprised of alternating high refractive materials and low refractive materials. The IR film has transmittance and reflectance characteristics capable of withstanding and operating effectively at an elevated temperature of, for example 600° Celsius, for a prolonged period of time. The IR film 118 advantageously allows visible radiation to pass through the envelope 102 while reflecting IR radiation towards the filament 104.
In the first embodiment, as shown in
In developing the invention, it was determined that IR radiation escapes the envelope 102 even when it is covered by the IR reflective coating 118. In particular, the coating is less effective at acute angles measuring less than approximately thirty degrees (30°) from the major axis A of the ellipsoidal portion of the envelope 102 and at obtuse angles measuring approximately one hundred fifty (150°) from the major axis. The totally reflecting coating reflects the IR radiation (as well as the visible radiation) that is escaping at these angles towards the filament. By preferentially reflecting this IR radiation (and also the visible radiation) towards the filament 102 that would otherwise pass through a lamp envelope having only an IR film, the efficacy of the light source 100 is improved. In the first embodiment as shown in
It is estimated that lamp efficacy may be improved on the order of approximately four percent (4%) by using the totally reflective end coatings on the ends of the envelope. The end coats are relatively inexpensive to add since they involve only a single layer and the technology of coating silver, aluminum, or a similarly functional reflector material is well known.
Although there is consideration that heating of the tubes in the embodiment of
It will also be appreciated that when the filament is used in a directional lighting system, the system can be optimized by matching the reflective end coat region with the desired reflecting areas of the reflector. Thus, as illustrated in
The invention has been described with reference to the preferred embodiments. Obviously modifications and alterations will occur to others upon a reading and understanding of this specification. For example, although a double-ended envelope is illustrated, single-ended lamps where the lead wires extend from the same end of the lamp are also contemplated. The invention is intended to include all such modifications and alteration in so far as they come within the scope of the appended claims or the equivalents thereof.
This is a continuation of application Ser. No. 09/603,025, filed Jun. 6, 2004, abandoned.
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Number | Date | Country | |
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20040104678 A1 | Jun 2004 | US |
Number | Date | Country | |
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Parent | 09603025 | Jun 2000 | US |
Child | 10714790 | US |