1. Field of the Invention
The present invention generally relates to a light source, and more particularly to a light-emitting diode (LED) based signal lights. The present invention provides for a method of creating a more efficient signal light.
2. Description of the Related Art
Signal lights, such as yellow traffic lights or rail signals for example, provide visual indications. Previous yellow LED lights generally exhibit relatively poor energy efficiencies due to high degradation in light output at extreme temperatures, high or low. For example, traffic signal head temperatures can exceed 74 degrees Celsius (° C.) due to solar loading. The internal heating of each colored module of a traffic signal also contributes to the temperature rise.
Consequently, poor energy efficiencies may increase material costs, energy costs, and reduces the signal light life due to internal heating of electronic components. Reduced efficiencies may also limit the light intensity of the signal and create safety risks. Proper intensity levels are required, for example, on warm days with high solar loading as well as cooler days.
Therefore, there is a need in the art for an improved signal light, e.g. a traffic signal light, rail signal light and the like.
In one embodiment, the present invention provides a method for creating an improved traffic signal light. The improved traffic signal light may utilize LEDs of improved efficiency at high temperatures. The LEDs of improved efficiency may be used alone or may be combined with one or more other types of LEDs. For example, the signal light comprises a housing, at least one outer lens and at least one or more second type of light emitting diodes (LEDs) deployed in the housing. The at least one or more second type of LEDs includes a pump, a phosphor and a filter having a cutoff point less than or equal to 540 nanometers (nm). The at least one or more second type of LEDs also has a pump peak wavelength less than or equal to 430 nm and has a phosphor with a peak wavelength greater than 575 nm.
An exemplary method of creating the signal light comprises providing a housing, providing at least one outer lens and providing at least one or more second type of light emitting diodes (LEDs) deployed in the housing. The at least one or more second type of LEDs includes a pump, a phosphor and a filter having a cutoff point less than or equal to 540 nanometers (nm). The at least one or more second type of LEDs also has a pump peak wavelength less than or equal to 430 nm and has a phosphor with a peak wavelength greater than 575 nm.
The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The outer lens 102 may be smooth or may have a scattered surface depending on if the outer lens 102 simultaneously serves as a filter (not shown) and/or serves as the mixing lens 104, as discussed below. The outer lens 102 may also comprise optical features to help diffract light into a desired angular direction.
LEDs 108 may be placed in a reflector 106. Reflector 106 may comprise individual reflector cups for each one of the LEDs 108. LEDs 108 may comprise one or more first type of LEDs and one or more second type of LEDs. The one or more first type of LEDs may emit a light energy having first dominant wavelength peak, for example a dominant wavelength peak of approximately 595 nanometers (nm) having an orange-yellow color. The one or more second type of LEDs may emit a light energy having a second dominant wavelength peak, for example a dominant wavelength peak of approximately 450 nm having a perceived white color via use of a blue LED coated with a yellow phosphor. Hereinafter, “white LEDs” refer to the perceived white color via use of a blue LED coated with a yellow phosphor, discussed above.
The phosphor material can have a significant effect on the color and efficiency of the LED. Some example phosphor materials include yttrium aluminum garnet (YAG), terbium aluminum garnet (TAG), and europium doped silicates. Phosphors can also be made by bonding the phosphor to a ceramic plate and mounting the plate over the LED die. This can provide better color consistency and therefore would be advantageous in the present invention. Although orange-yellow and white colored LEDs are used in exemplary embodiments of the present invention, one skilled in the art will recognize that any combination of color LEDs (e.g. a single color LED or different color LEDs) may be used within the scope of the present invention.
In one embodiment, the one or more second type of LEDs may be a blue LED using a yellow phosphor to convert most, if not all, of the blue light to yellow light. In another example, an ultraviolet (UV) LED is used with a phosphor to create a new color such as yellow. The blue or UV color is also known as the “pump” when used to excite a phosphor. In another embodiment a pump is used to create a green color. Hereinafter, “PC new” refers to the perceived phosphor converted new color via use of a pump LED coated with a phosphor. In some cases the PC new LED may be more efficient than the LEDs that created the color directly without the use of a phosphor conversion. In this case it may not be necessary to mix a first and second LED. Consequently, only the one or more second type of LEDs may be needed in the traffic signal light 100, as discussed below. In other words, none of the one or more first type of LEDs may be needed.
In an exemplary embodiment of the present invention, the one or more first type of LEDs and the one or more second type of LEDs may be placed adjacently in reflector 106 in an alternating fashion. In this case, the reflector 106 may serve to change LED light distribution. In one embodiment, the reflector helps concentrate the light into the lenses. This may also help mix the light by overlapping the light of the one or more first type of LEDs with the light of the one or more second type of LEDs. In another exemplary embodiment, the traffic signal light 100 may be comprised of only the one or more second type of LEDs. In some cases, the pump and the phosphor may not have exactly the same angular light intensity distribution. This can result in color variability on the lens. In this case, the reflector may facilitate better light mixing by changing the angular distribution of the pump light and the phosphor light. However, embodiments of the present invention are not limited to any particular arrangement and LEDs 108 may be placed in reflector 106 in any way.
Reflector 106 may be connected to a circuit board 110 via a plurality of wires 112. Circuit board 110 may include a processor for controlling the LEDs 108 on reflector 106. The reflector 106, the circuit board 110 and the plurality of wires 112 may be enclosed in a housing 114.
Traffic signal light 100 may also comprise a filter (not shown). The filter may be integrated into the outer lens 102, may be a separate lens located anywhere between the LEDs 108 and the outer lens 102 or may be placed directly over each of the LEDs 108. It may be desirable to place the filter directly over the LEDs in cases where it is preferable to use a non-tinted outer lens with little or no color. The filter may be a colored filter or a dichroic filter. Filtering may be performed in any method as is well known in the art of traffic signal light filtering.
In an exemplary embodiment, the filter may filter the one or more second type of LEDs emitting the light energy having the second dominant wavelength peak such that only a third dominant wavelength peak passes from the one or more second type of LEDs. For example, if the second type of LEDs are white colored LEDs, then the unfiltered white LEDs may have a dominant wavelength peak of approximately 450 nm. However, when filtered, the white LEDs may have a dominant wavelength peak of approximately 580 nm. In such an embodiment, the 580 nm dominant wavelength occurs because the filter blocks most of the 450 nm dominant wavelength, but transmits a portion of the phosphor emission originating from the phosphor coating with the new dominant wavelength. This is shown in
In one example as illustrated by
A cutoff point for the filter may be calculated by determining what dominant wavelength peak is desired without sacrificing efficacy (lumens/watt). For example, filtering white LEDs may not provide any better efficacy than the yellow AllnGaP LEDs currently used in traffic signal lights. To resolve this problem, the cutoff point of the filter may be increased or decreased in order to change the resulting dominant wavelength. In one embodiment, the cutoff point is set to approximately 550 nm +/−40 nm such that more light may be transmitted and the efficacy may be improved. As mentioned earlier, it may not be necessary to mix the one or more first type of LED and the one or more second type of LED. Only the one or more second type of LED may be used if the one or more second type of LED is a PC new LED that is highly efficient. In this case, the cutoff point can be critical and can be chosen in order to block a portion of the pump LED light and transmit a portion of the phosphor light generated from the phosphor emission in a manner that results in a final dominant wavelength with chromaticity coordinates within a desired boundary. As stated earlier, better color consistency can be achieved by using a phosphor that is bonded to a ceramic plate and attached to the LED die. In one embodiment, a filter with a cutoff point is used with a ceramic plate bonded phosphor LED in order to achieve even better color consistency. In one embodiment, the pump peak wavelength is less than or equal to 430 nm for the one or more second type of LED, e.g., the PC new LED. In one embodiment, the phosphor peak wavelength is greater than 575 nm for the one or more second type of LED, e.g., the PC new LED. In one embodiment, the cutoff point is less than or equal to 540 nm. This may provide a yellow color when used with a phosphor LED. In another embodiment, the cutoff point is less than or equal to 550 nm and may provide a more orange-yellow color when used with a phosphor LED. In a further embodiment, the cutoff point is less than or equal to 520 nm and may provide a more green-yellow color when used with a phosphor LED. In an even further embodiment, the cutoff point is greater than or equal to 590 nm and may provide a more orange or red color when used with a phosphor LED. In one embodiment, the filter passes at least 70% of the light at about 600 nm. In one embodiment, the filter passes not more than 30% of the light at about 425 nm. One skilled in the art will recognize that the cutoff point can also be raised, lowered or modified to achieve a desired dominant wavelength peak or chromaticity coordinates. In one embodiment, the dominant wavelength of the non-filtered PC new LED is between 580 nm and 595 nm. In one embodiment, the range of chromaticity coordinates for the light energy exiting the signal may be as shown below by Table 3.
However, when using two different LEDs (e.g. the one or more first type of LEDs and the one or more second type of LEDS) the filtered white LED may have a dominant wavelength peak of approximately 580 nm resulting in a green-yellow color. To resolve this problem, the mixing lens 104 may be used to mix two light energies having different dominant wavelength peaks to achieve a light energy having a desired dominant wavelength peak, as discussed below.
Referring to the mixing lens 104, in an exemplary embodiment mixing lens 104 may be integrated into the outer lens 102 that also functions as the filter, as discussed above. In such an exemplary embodiment, outer lens 102 may comprise a scattered surface to mix the light energies of the first and second type of LEDs. In an alternate embodiment, the mixing lens 104 may be a separate lens such as, for example, a Fresnel lens.
Alternatively, mixing of the light energies emitted from the one or more first and second type of LEDs may occur without a physical device such as mixing lens 104. For example, mixing of the light energies emitted from the one or more first and second type of LEDs may be done by proper positioning of the one or more first and second type of LEDs. As such, one skilled in the art will recognize that any mechanism for overlapping or mixing light energies emitted from the one or more first and second type of LEDs may be used such as, for example, using a physical device or structure or using proper positioning of the one or more first and second type of LEDs.
The mixing lens 104 may combine the light energy having the first dominant wavelength peak emitted from the first type of LEDs and the light energy having the third dominant wavelength peak emitted from the filtered second type of LEDs to produce a light energy having a desired fourth dominant wavelength peak. For example, the fourth dominant wavelength peak may be desired because it falls within a pre-defined range, as discussed below. Alternatively, if the fourth dominant wavelength may be achieved using only the one or more second type of LEDs, then only the one or more second type of LEDs may be used. Consequently, the mixing lens 104 may serve to mix the spectral light only from the one or more second type of LEDs.
In an exemplary embodiment, the first type of LEDs may be made of aluminum indium gallium phosphide (AllnGaP) and the second type of LEDs may be made of indium gallium nitride (InGaN). Moreover, in an embodiment where only the one or more second type of LEDs are used, the one or more second type of InGaN LEDs may be the PC new LEDs described above. However, LEDs 108 may be any combination of LEDs made of any type of materials typically used to construct LEDs.
Similar to LEDs 108 of traffic signal light 100 discussed above, LEDs 204 of traffic signal light 200 may also comprise one or more first type of LEDs and one or more second type of LEDs. Alternatively, the traffic signal light 200 may contain only one or more of the second type of LEDs. The one or more first type of LEDs may emit a light energy having a first dominant wavelength peak and the one or more second type of LEDs may emit a light energy having a second dominant wavelength peak. In an exemplary embodiment of the present invention, the one or more first type of LEDs and the one or more second type of LEDs may be placed adjacently in reflector 206 in an alternating fashion. However, embodiments of the present invention are not limited to such an arrangement and LEDs 204 may be placed in reflector 206 in any way.
Moreover, one skilled in the art will recognize that traffic signal light 200 may be similar to traffic signal light 100 in all other respects except the type of LED that is used, e.g. Hi-Flux LEDs or 5 mm discrete LEDs. For example, although
Consequently, the exemplary embodiment of the signal light illustrated in
Alternatively, if a yellow LED is made with InGaN technology it would provide a large performance improvement if used in the traffic signal light for yellow traffic signals. As a result, a yellow InGaN LED may be used for embodiments described above where only the one or more second type of LEDs are used in traffic signal light 100 and 200. An example of such an InGaN LED able to achieve the desired yellow color is a PC new LED described above.
However, LEDs made from InGaN have a higher efficiency than LEDs made from AllnGaP as temperatures increase. In other words, LEDs made from InGaN, such as white colored LEDs for example, have less light degradation as the temperature increases, as illustrated by line 302 in graph 300. As shown by graph 300, at 74° C. a white LED made from InGaN may lose only approximately 10% of its light output.
However, in an exemplary embodiment of the present invention, to use white colored LEDs made from InGaN, the white colored LEDs may be filtered such that only yellow colored light passes. However, the yellow colored light emitted from the filtered white LED may still be outside a pre-defined range. For example, the pre-defined range may be the wavelength requirements for traffic signals as defined by a regulatory agency or by a particular city. For example, some cities may require that a yellow signal light have a dominant wavelength peak of approximately 590 nm. However, the yellow light emitted from the filtered white LEDs may have a dominate wavelength peak of approximately 580 nm.
The color of the emitted light energy from an unfiltered and filtered LED may also be described in terms of coordinates of a chromaticity diagram, as illustrated in
However, as noted above, using the filtered white LED made from InGaN may still emit light having a dominate wavelength peak that is outside of a pre-defined range. To create a light energy having a desired dominate wavelength peak, the light energy of the filtered white LED may be mixed with a light energy of another LED, as described above. For example, the other LED may be an orange-yellow LED having a dominate wavelength peak of approximately 595 nm. Although an orange-yellow LED and white LED are used in an exemplary embodiment of the present invention, one skilled in the art will recognize that any combination of colored LEDs may be used within the scope of the present invention. The color combination of the LEDs may be determined by a final desired color. For example, a different color combination of LEDs may be used to achieve a red signal light.
By mixing the filtered white LED light energy with the light energy of the orange-yellow LED, a light energy may be created having a desired dominate wavelength peak within the pre-defined range, e.g. approximately 590 nm. An example of this is illustrated in
As discussed above, the light energy of a filtered white LED may have a dominant wavelength peak of approximately 580 nm, illustrated by mark 602. An exemplary range of chromaticity coordinates for a filtered white LED may be as shown below by Table 1.
Exemplary range of chromaticity coordinates for a filtered white LED.
Although the filtered white LED may have a yellow color, the yellow color of the filtered white LED may still be outside the pre-defined range. For example, mark 602 is outside of the dashed line 608 representing the pre-defined range. However, a light energy from another LED, for example a light energy from an orange-yellow LED, may be mixed with the light energy from the filtered white LED. For example, the light energy from the orange-yellow LED may have a dominant wavelength peak of approximately 595 nm, illustrated by mark 604. An exemplary range of chromaticity coordinates for an orange-yellow LED may be as shown below by Table 2.
Exemplary range of chromaticity coordinates for an orange-yellow LED.
Mixing the light energy from the orange-yellow LED with the light energy from the filtered white LED may create a new light energy having a dominate wavelength peak of approximately 590 nm, as illustrated by mark 606. Alternatively, as discussed above, the dominate wavelength peak of approximately 590 nm, as illustrated by mark 606, may be achieved by using only the one or more second type of LEDs, e.g., the PC new LED described herein. The new light energy may have a dominate wavelength peak that falls within the pre-defined range. This is illustrated by mark 606 being within dashed-line 608 representing the pre-defined range. This range is shown in Table 3a. An exemplary range of chromaticity coordinates for the new light energy may be as shown below by Table 3b.
Exemplary range of chromaticity coordinates for an orange-yellow LED.
As a result, the exemplary embodiment of the signal light illustrated in
At step 704, method 700 may provides at least one outer lens.
At step 706, method 700 provides one or more second type of light emitting diodes (LEDs) deployed in the housing, wherein the at least one or more second type of LEDs comprises a pump, a phosphor and a filter having a cutoff point less than or equal to 540 nanometers (nm). The at least one or more second type of LEDs has a pump peak wavelength less than or equal to 430 nm and has a phosphor with a peak wavelength greater than 575 nm.
In one embodiment the one or more second type of LEDs may be made of indium gallium nitride (InGaN). Moreover, in another embodiment the one or more second type of InGaN LEDs may be PC new LEDs described above. Method 700 concludes after step 706.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/618,512, filed on Dec. 29, 2006, entitled METHOD AND APPARATUS FOR PROVIDING A LIGHT SOURCE THAT COMPINES DIFFERENT COLOR LEDS, which claims priority under 35 U.S.C. § 119 (e) to U.S. provisional patent application Ser. No. 60/755,704, filed on Dec. 30, 2005, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60755704 | Dec 2005 | US |
Number | Date | Country | |
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Parent | 11618512 | Dec 2006 | US |
Child | 12055544 | US |