BACKGROUND OF THE INVENTION

Cross Reference To Related Application(s)

This application claims priority from U.S. Provisional Patent Application Serial No.

61/199,163 filed November 12, 2008, and which is incorporated by reference herein. Field of the Invention The present invention relates to a device and method for improving LED efficiency and more particularly to cooling an LED to improve efficiency and life. The present invention also relates to a device and method for improving integrated circuit and/or chip performance by cooling. Description of the Related Art The problem of keeping LEDs cool in order to produce maximum light output from the

LEDs has existed for quite some time. Numerous attempts have been made to solve this problem. Some, such as in U.S. Patent No. 7,252,385 to Engle et al, have used heat exchangers, heat sink fins, and forced air cooling of the fins, to cool an LED. Others, such as in U.S. Patent No. 6,452,217 to Wojnarowski et al, have used a phase change material (such as waxes or eutectic salts) on a metal mesh or foam to help dissipate heat. These methods and apparatus, however, have relied on conducting heat away from the LED by using a heat conductor such as a metal substrate to remove the heat and conduct it to the metal mesh or to the heat exchanger or heat sink.

In U.S. Published Patent Application Publication No. 2005/0111234 to Martin et al, an LED lamp has a shell that looks like an incandescent bulb shell, and there is an optical reflector. The LED is mounted on a heat sink that is disposed within the shell. Cooling air is blown into the LED lamp structure and over the heat sink. Apertures for inlet and exhaust for the air may be defined by the shell and reflector. This apparatus also uses a heat conductor to remove heat. Below is a brief overview of some characteristics of Light Emitting Diodes (LEDs)

A diode is an electrical device which allows current to flow in only one direction, called the forward direction. It can be thought of as a one-way valve, or check valve for electricity. As shown in FIG. 1 a diode 1 is made of a P-type material 3 and an N-type material 5 with a junction 4 at their common boundary. Contacts 2, 6 on their surfaces allow wires to be attached to the device. In an LED, the junction is the place where the light is produced. The amount of light depends on the current passing through the junction and on the temperature. An LED emits light when current flows in the forward direction. FIG. 2 shows a graph of forward current in milliamps (mA) as a function of forward voltage for an LED, which graph is from LEDs Magazine of August 2007 located at HTTP://www.ledsmagazine.com/features/4/8/l ("LEDs Magazine"). This graph shows the typical electrical operating characteristic of an LED.

The device will not turn on (pass current) until a threshold voltage is achieved. The threshold voltage and slope of the line will vary with material. The slope of the line represents the resistance of the device. As current flows, some of the power is dissipated as heat. An LED can get quite hot, greater than 120 ⁰ C. High temperatures decrease the luminous efficiency.

FIG. 3 is also from LEDs Magazine. As the forward voltage increases, so does the current, and temperature. Therefore, LEDs are usually driven with a constant current supply. This graph illustrates the decrease in forward voltage as the temperature increases.

FIG.4 is also from LEDs Magazine and shows that as the drive current increases, the luminous efficiency decreases. The red line represents forward current and the blue dotted line represents light output/efficiency. The graph shows a drop in efficiency of about 70% at 1 amp. FIG. 5 is also from LEDs Magazine. It shows that as the juriction temperature increases, the luminous output drops dramatically. More specifically, this graph shows the decline in light output for different color LEDs with increasing temperature. Room temperature is taken as 25°C or 77°F. One can see a dramatic drop, e.g., at 130 ⁰ C or 266°F. It is easy to see how keeping the junction cool will result in vastly increased luminous efficiency. A device which could keep temperature at the junction around 38 ⁰ C or 100 ⁰ F and which would enable more current to pass at the junction without raising the temperature would produce more light.

FIG. 6 is a graph from http://www.ecse.φi.edu/~schubert/Light-Emitting-Diodes-dot- org/chapl2/chap 12.htm. Different colors are emitted from different materials. Red and amber come from one type of material, blue and green come from another type of material. This graph shows the typical current and voltage relations for such two materials at room temperature.

What is needed is a way to improve cooling to improve the light output efficiency of LEDs. In addition, in integrated circuits (formed as chips typically), an improved cooling system is needed too.

SUMMARY OF THE INVENTION

The thermal control techniques in accordance with embodiments herein have applications for cooling LEDs and many other electronic devices. Because there are several deficiencies inherent in the packaging design of commercial LEDs, embodiments of the invention are most particularly suited for LEDs, which deficiencies include:

1) Thermal control issues. When the diodes operate, they get hot, losing efficiency and reducing lifetime. 2) Light collection efficiency. Much of the light that is generated in commercially available chips is not usable because the design does not take advantage of the light produced. The present inventor has tested specially manufactured red and blue diodes, i.e., three watt (40 mil) and one watt (20 mil), respectively. When these diodes are assembled using the method and structure of a preferred embodiment of the present invention, they produce 200% to 500% more usable light than commercially available devices. With such improvements, manufacturers will be able to use smaller chips, increasing yield, and reducing costs. Brighter and more efficient devices are possible.

Thermal control issues The LED chip gets hot. When the chip, and in particular, the junction, heats up the light output drops. Chips having red and amber light are created using AlGaInP (aluminum indium gallium phosphorus) and are more temperature sensitive than chips having blue and light green use InGaN (indium gallium nitride). See FIGs. 5 and 6.

At a junction temperature of 130 ⁰ C, a red LED may experience an output drop of eighty percent from room temperature output. Light production from blue and green LEDs may drop about forty percent. In addition, increasing temperature increases wavelength about 0.03 to 0.13 nm/°C, depending on the material, thereby altering the emitted light color.

Chips are typically mounted to a substrate with conductive material (usually silver filled epoxy) and covered with a clear plastic encapsulant. This encapsulant is usually silicone because it can tolerate processing temperatures. The only thermal path that is available is through a conductive die attachment. The sides and top of the device are effectively insulated. FlG. 7 shows a typical LED chip in a package 8. Chip 9 is mounted on a pedestal back 10 functioning as a heat sink, and a circuit board 12. For a two and one half watt blue diode, the chip is the same size as a three watt Luxeon brand (40 mils) with a Seoul Semiconductor brand star type mounting. The chip has a clear lens 1 1 of diameter approximately 0.2".

Nomenclature The chip, lens, and lead assembly are called an emitter (shown by reference number

13). Star type mounting refers to the assembly pictured in FIG. 7, where the emitter is mounted to an aluminum backed circuit board with six sides and curved notches in between each of the sides. The Star package is typically attached to a larger heat sink. Thermally conductive paste between the two elements insures good heat transfer. In a test set-up to measure brightness of commercial two and a half and three watt diodes, each diode is mounted to an aluminum heat sink using heat sink compound. The aluminum is painted mat white to match the interior of an integrating sphere and has the following dimensions: 4" x 4" x 1/8" thick. The star package is approximately one inch in diameter. Issues with light collection

Light is generated in the junction that is parallel to the large surfaces. It travels in all directions. Light that strikes the inside surface of the chip may or may not escape, depending on the angle and the difference in refractive index of the chip and the surrounding media according to Snell's law. Light that travels downward is virtually lost. Light that travels to the sides is not effectively collected by commercial devices. In small LEDs (less than one watt, e.g., 0.08 watts) the situation is worse. The chip is placed in a depression at the end of a lead frame. Approximately one eighth of the light generated is directed in the forward direction (assuming a 45° cone). There are additional losses from scattering, etc. In larger LEDs, the encapsulating lens captures the light traveling in the forward direction and very little from the sides. The end result is that about twenty five percent of the generated light is sent toward the lens.

Small LEDs In FIG. 8, there is shown a small LED package 20, e.g., a five millimeter diameter package. Note that a chip 22 and phosphor 23 are held in a conical shaped depression of a lead frame 24 of leads 25, 26. A clear plastic lens 27 covers the chip and phosphor, and has a base 28.

FIGs. 9 and 10 show a white LED 30 from http://www.ecse.rpi.edu/~schubert/Light- Emitting-Diodes-dot-org/chap21 /chap21.htm. These figures are a more detailed representation of a typical small white LED. A chip 31 is located in the bottom of a depression or cavity 32a and covered with phosphor laden plastic 33 (usually silicone). Only light, e.g., phosphorescence 35 and blue luminescence 36, that is emitted into an opening of cavity 32 escapes. Most of the light is wasted. Bond wires 34 connect chip 31 to header 32. See also FIG. 8. The chip is e.g., a GaInN blue LED chip in a phosphor encapsulating die for converting phosphorescence and blue luminescence to white light.

Issues with phosphors (white light)

White light is not produced directly by LEDs. It is produced by directing the light through phosphors. A "blue" LED illuminates a phosphor, or phosphors, which re-emit the light at lower wavelengths. The resulting light appears as approximately white light and thus a "white" LED. In a typical commercial diode, the phosphors are mixed into a coating that is applied around the chip. As phosphors heat up, their efficiency drops. The chip and phosphors both heat up. The temperature of the chip can exceed 100 ⁰ C. At http://www.ecse.φi.edu/~schubert/Light-Emitting-Diddes-dof- org/chap21/chap21.htm, there are figures showing LEDs shining light through phosphor layers.

A three watt white LED manufactured by Cree, Inc. (of Durham, N.C.) with a star type mounting has a clear dome lens which is located above a yellow phosphor. Only light emitted in an upward direction escapes from the mounting. Side emitted light is blocked by the package. The lens diameter is 0.18".

One watt blue diode mounted on copper strips is manufactured by Optek Techonolgy of Carrollton, Texas. There is a square chip in the center of the depression of the package. Clear silicone covers the chip. Light emitted to the side hits the interior of the depression or cup. Light emitted to the bottom or back is lost. The package is soldered to copper strips to conduct heat away and to provide electrical connections.

One watt daylight white diode manufactured by Optek Technology has yellow phosphor mixed with silicone covering the chip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a conventional LED structure;

FIGS. 2-6 are graphs of various performance characteristics of conventional LEDs;

FIGS. 7-10 are schematic side views of other conventional LED structures; FIGS. 11 and 14 are partial schematic and partial sectional views of LED assemblies in accordance with a first embodiment of the invention;

FIGS. 12 and 13 are LED packages that are and may be disposed in the LED assemblies of FIG. 11 or 14;

FIG. 15 is a top view of a portion of the assemblies of FIGS. 11 and 14; FIGS. 16-20 are graphs of experimental results using LED assemblies in accordance with embodiments of the invention in comparison with conventional LED devices;

FIGS. 21-22 and are schematic and partial sectional views of various additional LED assemblies in accordance with additional embodiments of the invention; FIG. 23 is a schematic view of an LED assembly in accordance with a further embodiment of the invention;

FIG. 24 is a diagram of a portion of an LED assembly in an elliptical cavity in accordance with a variation of embodiments of the invention;

FIG. 25 is a schematic and exploded side perspective view of a portion of an LED assembly including a housing or heat sink with a cover in accordance with an embodiment of the invention;

FIGS. 26-27 are side partial schematic and partial sectional views of additional embodiments of the invention for an integrated circuit assembly;

FIG. 28 is a schematic view of a traffic light having its cover removed for explaining testing conducted on embodiments of the invention;

FIG. 29 is a schematic front view of an LED assembly in accordance with a another alternative embodiment of the invention;

FIG. 30 is a schematic side view of the LED assembly of FIG. 29; and

FIGS. 31-34 are graphs of experimental results using LED assemblies in accordance with embodiments of the invention in comparison with conventional LED devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Embodiments of the present invention increase overall efficiency As shown in FIG. 11 , there is a housing or heat sink 46a having a" recess or cavity 47a formed therein, in which an LED 42a with lead 43a is disposed. The LED has coolant liquid 48a around it. A cover 49a (or lens) may be used to seal coolant liquid 48a in the housing.

In a test set up, the following LED chips were mounted to TO-5 headers made by IH-V Compounds, Inc. (of New York, NY):

Blue one watt (20 mil chip); Red three watt (40 mil chip) Yellow three watt (40 mil chip) (Yellow test results not reported here) 20 mil = 0.02" = V ₂ millimeter; 40 mil = 0.04" = 1 millimeter FIG. 12 shows a set up in a side view diagram and FIG. 13 is a top view. There is a three watt (40 mil) chip 41 mounted to a TO-5 header 42. (A TO-5 package is made, e.g., by National Semiconductor Corporation of Santa Clara, CA.) The chip's electrical connections are least 43. One mil gold wire 44 can be seen between the top of the chip and a post 45 (1 mil = 0.001").

In tests, chip 41 with header assembly 42 is placed in an aluminum reflector 46 having a cavity 47 and coolant fluid 48 shown in FIG. 14. The arrangement serves at least three purposes:

1) Reflector 46 captures side emitted light.

2) Cavity 47 of reflector 46 is tillable with coolant fluid 48 to cool chip 41 and header 42. 3) The aluminum of reflector 46 provides a thermal path to remove heat from cavity

47.

Although aluminum is preferred for reflector 46 (or at least for the surface of cavity 47), other materials that provide for reflectivity combined with heat conduction, and especially with light weight, would and should work as well. Also, a material that has good heat conduction and is lightweight may be coated with an aluminum surface (e.g., by deposition) to achieve sufficient reflectivity. In addition, a material that might be heavter than desired could be used as the reflector housing in a nonsolid structure.

The header assembly was secured with a liquid tight seal inside the small end of a polished aluminum reflector. The cavity is shaped approximately like a parabola or ellipse. FIG. 15 shows a forty mil chip 41 mounted or fixed to a TO-5 header 42 installed in a reflector 46 with cooling fluid (e.g., oil) in cavity 47.

Two sizes of reservoir were tested: Large and small. The cavity above the header is filled with cooling fluid (the oil). Pictured in FIG. 15 is the smaller version ("configuration II"). The diode is just at the threshold of turning on, i.e., it is just beginning to produce light. Configuration II was made with a cavity of about a diameter of a dime, and configuration I was about a diameter of a quarter. The LEDs are installed in heat sink/reflectors which are all otherwise the same in accordance with a preferred embodiment of the invention.

Liquid cooling: In order to effectively remove heat from the chip, the chip is surrounded with a liquid bath. The coolant liquid is a heat transfer medium that allows heat to move away from the chip and into the finned heat sink (the aluminum reflector structure). Three (3) liquids were tested:

1) Perfluoroether - HT-170 and HT-135 from Solvay Solexis SpA (of Milan, Italy), having a boiling point 150 ⁰ C. Perfluoroether worked. The oils are preferred because they are less costly and do not have any effect on the ozone layer. Moreover, perfluoroether is not as preferred as the other liquids disclosed herein because the perfuoroether failed when the LED was over driven with too much power. Specifically, during testing, a small stream of bubbles was seen. Then, the one mil gold wire melted. It appeared that a bubble formed around the wire and allowed it to overheat. The melting point of gold is 1064.18 ⁰ C, 1947.52 ⁰ F. (Power at the failure was greater than seven watts on the one watt blue chip). 2) Poly Alfa Olefin (PAO) - Hi-Low oil, i.e., Huskey™ Hi-llow Series oil, ISO 22 from Husk-Itt Corporation (of Norco, CA). This Hi-Low oil had a viscosity of 22 centi- stokes, a flash point of 440 ⁰ F, and a pour point of -82°F.

3) Mineral oil, USP - Rite-Aid® mineral oil had a flash point of 135°C (275°F), and an autoignition temperature of 260 - 370 ⁰ C (500 - 698°F).

Both oils, the PAO and mineral oil, were clear "water white" in appearance. No difference was seen between their optical performances. The temperature of the oil was measured with a small type K thermocouple. The oil temperature stayed around 100 ⁰ F, so there was no fire hazard. See the graphs of FIGS. 16-17. Configurations:

Two cooling reservoir volume sizes were used: Configuration I = about 1 milliliter (Larger) Configuration II = about 0.2 milliliters (Smaller)

As seen from FIGS. 16 and 17, the smaller reservoir retrieves about 30% more light than the larger reservoir. This may be because of the reflector geometry.

Test results comparing commercial (Luxeon) red three watt diodes with our equivalent 40 mil (lmm) chips. Also included is a one watt (20 mil) diode from Optek. The graph of FIG. 17 has the following key:

X HI-V (Configuration II); Δ III-V (Configuration I); 0 Luxeon three watt; D Optek one watt

As seen in Fig. 18, in the case of blue diodes, the Configurations I and II of the inventive embodiments with a smaller (20 mil) chip can outshine a blue larger (40 mil) Seoul diode in brightness.

Additional Blue diode testing: Further testing with 20 mil chips in accordance with Configurations I and II of the invention and a Seoul Semiconductor 40 mil chip was conducted. The chips in accordance with Configurations I and II are only one quarter of the size of the commercial diodes, yet they produce up to about 40% more light. See Figs. 33 and 34. This represents greater than a 400% efficiency increase for at least some embodiments of the invention. It can also be seen from the graphs that at least some embodiments of the invention produce about the same amount of light as a commercial chip (of four times the size) while only drawing about one half the power.

Additional Red diode testing:

Further testing of red diodes using 40 mil chips in accordance with Configurations I and II of the invention and a Luxeon 40 mil chip was conducted. The 40 mil chips in accordance with Configurations I and II of the invention produced the same light using as little as about 30% of the power, and produced as much as about twice the peak brightness. The 40 mil chips in accordance with Configurations I and II of the invention allowed significantly higher drive currents, i.e., as much as about 175% higher than the Luxeon 40 mil chip. At drive currents above two (2) watts, the Luxeon diode did not produce any significant additional light. There is no benefit for that additional energy.

In the experiments, as can be seen in the graphs, chips from HI-V Compounds were obtained and compared with chips prepared in accordance with embodiments of the invention, which chips simply used commercially available LEDs. Specifically, the chips that were used in the inventive configurations were manufactured by LUXEON. They were the same chips used in Luxeon diode devices. The dramatic performance improvements arising from the chips made in accordance with embodiments of the invention is shown in FIGS. 31 to 34. Test conditions Measurements were carried out with proper heat sinking in an integrating sphere. Readings were taken with a Pritchard Spectrophotometer. The test voltages were pure DC.

RED Configurations:

Two variations of the LED assembly in accordance with Configurations I and II of preferred embodiments of the invention were compared to commercial diodes.

Luxeon 40 mil - 3 Watt rated

Inventive LED assembly 40 mil - Configuration I and II

Also included is a one (1) watt (20 mil) diode from Optek. With reference to FIG. 31, the following should be noted: 1) The one watt and three watt commercial diodes (Optek and Luxeon) follow the same curve. Both have substantially similar thermal and optical issues.

2) The LUXEON diode is rated at three (3) watts but does not produce any additional light after two (2) watts in the experiment.

The LED assembly in accordance with embodiments of the invention delivered higher efficiency, up to about three times better. In addition, the LED assembly in accordance with embodiments of the invention needed as little as less than one third of the power that the Luxeon LED received in order to produce the same or about the same amount of light.

The LED assembly in accordance with embodiments of the invention delivered up to about two times the peak brightness of the commercially available LED. The LED assembly in accordance with embodiments of the invention (in configuration

II) produced as much as about twice or more of the light produced by a Luxeon three watt diode. It is envisioned that other embodiments of the invention may deliver significantly more light, e.g., greater than twenty percent more than the embodiments that were tested or even more than that. The LED assembly in accordance with embodiments of the invention achieved significantly higher drive currents, as much as about a 175% increase over the effective maximum drive currents achieved by the tested commercially available LED assemblies.

The LED assemblies in accordance with embodiments of the invention were driven at up to about 3.5 watts while the Luxeon diode that was tested saturated at a peak output of only about two watts. At greater than about two watts, the Luxeon diode that was tested did not produce any additional light, even though it was rated at three watts. Driving it at three watts did not create additional light and caused the diode to get very hot and overheat.

Actual measured values for the testing are shown in FIG. 32. Blue configurations

Two variations of the LED assembly in accordance with Configurations I and II of preferred embodiments of the invention were compared to commercial diodes. Small chips (20 mil) and diodes rated at one watt in accordance with Configurations I and II of preferred embodiments of the invention were compared to large chips (40 mil) of commercially available diodes (by Seoul) rated at 2 V ₂ watts.

This dramatic chart shows that the LED assembly in accordance with Configurations I and II of preferred embodiments of the invention (a packaged chip at only one quarter of the size, produced up to about 40% more light than the commercially available Seoul diode.

Note that the Seoul chip that was used was a 40 mil size (normally or previously rated at three watt) but the one that was used was only rated at VA watts.

The LED assembly in accordance with Configurations I and II of preferred embodiments of the invention chip is only one quarter of the size of the commercial chip and still outperformed it. The LED assembly in accordance with Configurations I and II of preferred embodiments of the invention chip was up to about twice as good (efficient) as the commercially available chip based on the testing.

Considering size, the LED assembly in accordance with Configurations I and II of preferred embodiments of the invention chip was up to about eight times better in efficiency and light output.

The LED assembly in accordance with Configurations I and II of preferred embodiments of the invention chip needed as little as about one half of the power needed by the Seoul Semiconductor LED that was tested to produce the same or about the same amount of light. Additional embodiments of the invention are expected to further enhance efficiency and performance.

The small chip in accordance with embodiments of the invention out shined the large commercially available chip that was tested. Actual measured values are shown in FIG. 34.

Other comparisons: With reference to FIGS. 19 and 20, a one watt LED in accordance with a preferred embodiment was compared with a three watt blue LED. The one watt chip assembly was made using Configuration II - 0.2 ml reservoir with mineral oil.

At three watts, the diode having a twenty mil chip, and made in accordance with the preferred embodiment, produced 60% more light than the three watt Luxeon "Star." That is more than five times the light per unit area.

The diode having a one watt chip of the preferred embodiment produced as much light as the Luxeon three watt chip with only fifty percent of the power. Accordingly, it was twice as efficient.

Covered and other variations: Additional improvements in thermal control and light gathering a're possible in various variations of the preferred embodiments. As shown in FIG. 21, a clear cover 51 that seals in coolant fluid in a reflective walled cavity 52 may be used. LED Chip 53 is suspended inside the reflective cavity, e.g., using its lead wires 54. In this embodiment, a chip of any size can be used without an integral heat sink. An annular recess 56 is formed in reflector 55 to receive cover 51. The reflector structure functions like a heat sink and a housing for receiving the LED chip and coolant.

In addition, LED chip 53 optionally has a transparent back (bottom), so that light escapes the chip at its underside. That light is used too due to the reflective surface of cavity 52. In addition, better cooling than the previous embodiments occurs given suspension of the chip in the coolant fluid in cavity 52.

Numerous variations in assembly design and package size can be utilized. Light patterns can be shaped with reflective and diffractive optics. A few of the possible configurations are shown in FIGS. 22-25. In FIG. 22, there is a domed lens having a dome 61 and housing 65. In FIG. 23, there is a housing 65a which need not have a recess, and a hollow domed lens 61a. Specifically, in FIG. 23, chip 53 is shown with beam 67 of light (in addition to the chip's other light) emitted through the bottom and directed against a reflective coating of an area 62 of housing 65a (preferably a heat sink too). There is a hollow domed lens 61a over the cavity. In addition, in FIG. 24, there is a variation of cavity where it is elliptical. An elliptical cavity 72 has an LED chip 73 placed at one focus 72a of the ellipse and an optional phosphor plate 77 placed at or near the second focus 72b.

FIGS. 29 and 30 show a small LED package in accordance with another embodiment of the invention. In this embodiment, there is an LED assembly 101 having a housing in the form of or including an envelope 102 with a surface area of inner surface 102a that is preferably quite large compared to a surface area of a chip 104 having wires 105. The envelope is filled with cooling fluid 103 (e.g., oil). Cooling fluid 103transfers, e.g., by convection, heat generated by the chip to the envelope where it can be dissipated.

Heat is also removed through conduction via electrical pins 108. Reflective portions may be provided on surface 102a and/or on a substrate or base 107 in order to direct the light as desired. Base 107 may have a heat sink and/or the pins 108 may lead to heat sinks. Base 107 may be part of the housing and/or integral or unitarily formed with the envelope or separate.

The envelope is preferably made of a material that will readily conduct heat away, e.g., a metal such as aluminum, although it could be made of any other material sufficient to hold liquid. The pins 108 are preferably of metal, such as aluminum, and conduct heat away.

White light LEDs benefit from cooler phosphors (see FIGS. 10 and 11):

Current state of the art white LEDs have phosphor suspended in plastic directly surrounding the chip. The chip heats the phosphor and the phosphor efficiency drops accordingly. Luminous output efficiency might fall about one percent per degree Celsius (1% per ⁰ C). Thus, at 120 ⁰ C the phosphor luminous efficiency could be cut in half.

Keeping the phosphor cool is of obvious benefit. By placing a phosphor screen away from the chip, for instance at the clear cover over the reservoir, the phosphor temperature will be maintained in a much more favorable range.

FIG. 25 shows a white LED mock up prototype. A diode is to be sealed in cavity 82 in housing 85 (e.g., a heat sink too). A cover plate and phosphor screen are to be secured by a ring 85b on the right, and specifically press fit between an inner shoulder 85c of ring 85b and

{ an edge 85a of housing 85 around cavity 82. The ring 85b press fits, is epoxied or threads onto the housing 85 and is also preferably aluminum or other heat sink material. The cavity would be filled with heat transfer fluid. Phosphor cost savings:

Phosphors are costly. Using a small amount applied around the chip is attractive from an economic point of view. It is very unattractive from a heat control perspective.

One way to use less phosphor is to focus the light to a smaller area, and just apply the phosphor in that small region. There are many ways to accomplish this. One of the simplest methods is to employ the geometry of an ellipse as shown in FIG. 24. An ellipse has two focal points. Light originating at one of them will pass through the second focus. If the phosphor is placed at or near the second focus, only a small area need be covered and it will not be subjected to the heat of the chip. In FIG. 24, the dashed lines 79 represent the paths of light rays. Additional applications of the cooling oil: This approach of providing coolant liquid, such as oil, can be used in cooling other electronic devices, for instance, computer chips. At present, chips are embedded in plastic. In order to cool them, heat sinks are applied to the outside of the plastic. This is analogous to putting a heavy blanket over a fevered patient and placing an ice pack on top of the blanket in order to cool them.

In this embodiment, a package 90 such as shown in FIG. 26 may be used. This design eliminates the thermally insulating plastic and replaces it with heat transfer fluid 94. The fluid then transfers the heat to a metallic case 95 (thermally conductive case) enclosing the device (e.g., by sealing to base plate or substrate 92 and enclosing leads 93). In such a case, the integrated circuit(s) (chip or microprocessor 91 on a substrate 92) may be cooled in this way for use in any electronic device, e.g., CPUs, TVs, and/or DVRs. The integrated circuits may be suspended in the liquid where attachment to a substrate is not necessary using leads 93 (as in prior embodiments) or otherwise.

As shown in FIG. 27, cooling fins 96 and fans may be added in order to remove the heat. Liquid filled tubes may also be used as shown to remove heat from the package. Forming the reflector /reservoir:

Tool steel is hand ground to the desired profile. Then, the tool steel as profiled is mounted in a lathe and the aluminum round stock is turned, hand polished, and cleaned.

Light Output of LED Compared To Traffic Light The inventor combined a RED LED array with LEDs made in accordance with a preferred embodiment to a traffic signal (FIG. 28) on a test bench. Specifically, a 12" diameter traffic light made by General Electric model number DR6-RTFB -20A-22 (7.1 watts) was used.

On a testing bench, a blue diode undergoing life test, a diode in accordance with a preferred embodiment, and a red diode placed in an integrating sphere were tested as well as a traffic light with the lens cover removed. There were 105 individual LEDs in the traffic light. For the measurement, strips of paper painted mat white were placed between the rows of LEDs. The painted paper reflected light that was being scattered downward so that the light became directed up to the target in the same way that a coating on a sphere would do. A light output value in foot-lamberts per watt was measured for the traffic light and the red LED in accordance with a preferred embodiment by placing the top of the integrating sphere over the traffic light and over the LED:

Traffic light: 4.2 x 10 ³ foot-lamberts / 7.1 watts = 591 ft-lm/w

Red LED: 1.84 x 10 ³ foot-lamberts / 2.2 watts = 836 ft-lm/w (40% more efficient)

It would take only three such red LEDs to be about equal to the light output of the entire traffic light having 105 LEDs.

Without using the white strips in the traffic light, the LED in accordance with a preferred embodiment is seventy five percent more efficient and only two such LEDs would equal the entire traffic light output.

Test apparatus:

To test relative brightness, appropriate filters were built into a Spectrophotometer. The values were recorded in Foot-Lamberts. An integrating sphere was used. It was made from two stainless steel bowls painted mat white inside so that the surface was as optically scattering as possible. This insured that the region that was sampled was uniformly illuminated. A blue diode that was tested was located in the bottom of an integrating sphere. The diode was one (1) watt (20 mil chip) running at 2.55 watts. The integrating sphere's top, an underside of a tab was located at the back portion of the sphere. This is a target used to measure brightness. A three quarter inch diameter view port was located in a front portion of the sphere. The principal of operation is that light scatters from the surfaces and illuminates the top side of the tab. It is not illuminated directly by the light source.

An eye piece of optical head of a Pritchard Spectrophotometer, Model PR-1980A-OP was used to center a spot subtending an angle of six (6) minutes on the target to be measured. The spectrophotometer had a display. There was an optical head control panel of the spectrophotometer. The test bench used held all meters and power supplies used to power the LEDs under test.

Use of nanophosphors with the LED of the preferred embodiment

LEDs emit light in single colors. Phosphors can absorb light and reemit it at different wavelengths. In order to make white light from LEDs, blue or near-ultraviolet, light is absorbed by a phosphor. The light is reemitted at lower wavelengths.

In a typical commercial "white" LED, a whitish light is produced by combining a blue light with a yellow emitting phosphor. (Phosphor: YAG:Ce = Cerium doped yttrium aluminum garnet). The result is light with peaks in the blue and yellow. It does not include the entire visible spectrum. Therefore, color rendition is poor. Objects illuminated with this light

(predominately blue and yellow) do not look "natural" the way they would look in sun light.

A nanophosphor system would cover the entire visible spectrum. These devices would offer excellent color rendition.

A disadvantage of large phosphor particles is that they scatter light. In doing so a great deal of the light is lost. Nano size particles are smaller than a wavelength of light. They do not scatter light. They are transparent. Nano size phosphors range from a few nanometers to 1 ,000 or more nanometers in diameter.

A) With a non scattering phosphor system dispersed in the cooling liquid, the device would have exceptionally high efficiency. B) With a non scattering phosphor in a plastic window, the device would also have an exceptionally high efficiency.

Nano size phosphors offer several advantages.

1) They virtually eliminate light losses due to scattering. 2) They may provide higher refractive index for the liquid coolant. This will allow more light to escape from the LED chip increasing the efficiency.

3) A further advantage may be that in some nanophosphor types there will be a higher absorption coefficient. Nanophosphors, especially "caged" nanophosphors, have very high optical absorption similar to semiconductors. For composite nanophospher screens for detecting radiation having optically reflective coatings, see U.S. Patent No. 6,300,640 to Bhargava et al, incorporated by reference herein.

4) Based on U.S. Patent No. 6,300,640 and use of nanophosphor, a mixture of nanophosphors that give excellent color rendition for white light with no scattering losses is considered to be useful in conjunction with embodiments of the present invention. 5) The nanophosphors will operate at a lower temperature and higher efficiency.

The nanophosphors may be placed in the coolant e.g., in suspension, and placed on the cover, or just one or the other. Other cooling liquids:

Other cooling liquids that may be used may include gels, thixotropic liquids, and phase changing materials. The phase changing materials typically are solid and change to liquid when they get hot, and act as a coolant. Ideally, the coolant is nonelectrically conductive, but very heat conductive. The coolant must also pass substantial light emission, so as not to detract from the light emitted from the LED. However, the cooling liquid does not have to be thermally conductive. The cooling liquid removes heat and will still remove heat by convection. Other variations:

The structure of the LED need not be such that the diode is fixed on a substrate that is a heat sink, unlike a conventional diode. The diode can now be held in place by just the leads or otherwise suspended in the coolant liquid. This eliminates a manufacturing step of attachment to the heat sink/substrate. Further, if the diode is on an optically transparent substrate, this suspension enables capture of the light that comes out the back or bottom of the LED and reflecting that light upward thereby enhancing efficiency.

Although the invention has been described using specific terms, devices, and/or methods, such description is for illustrative purposes of the preferred embodiment(s) only. Changes may be made to the preferred embodiment(s) by those of ordinary skill in the art without departing from the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the preferred embodiment(s) generally may be interchanged in whole or in part.