Patent Application
20140160774
This invention relates generally to aviation equipment and, in particular, to aviation lights.
Dual-color anti-collision lights (ACLs) are used in numerous aviation applications, including the Royal Air Force, Australian, New Zealand, and United States Air Forces as well as numerous civilian applications. Typically, dual-color ACLs incorporate a white strobe having an effective luminous intensity of 1500-2500 cd for daytime operations and a red strobe having effective luminous intensity of 150-250 cd for nighttime operations. According to federal regulations and various international agreements, the chromaticity of the white strobe must meet the definition of “Aviation White” as defined, among other places, in Federal Acquisition Regulations (FAR) 25.1397. Similarly, the chromaticity of the red strobe must meet the definition of “Aviation Red” as defined by FAR 25.1397.
Conventional dual-color ACLs employ xenon flash tubes to provide the desired light output and chromaticity. A first xenon flash tube is positioned at the focus of a reflector positioned behind a clear lens to provide the white strobe output. A second xenon flash tube is positioned at the focus of a reflector positioned behind a red filter. Conventional dual-color ACLs have a limited operational life, require a comparatively heavy high-voltage power supply to operate the flash tubes, and must contain two separate optical systems, one each for the white and red strobes.
Light Emitting Diodes (LEDs) offer the advantage of improving reliability, reducing power consumption, and reducing the weight of a dual-color ACL. Achieving the desired effective luminous intensity, however, requires the use of multiple LEDs in place of a single xenon flash tube. Moreover, it is well known that white LEDs, which use a phosphor conversion to convert light output from a blue LED die into white light, exhibit a color shift with age and temperature. The effect is to cause the white LEDs to produce light that is more greenish as the phosphor deteriorates. As a result, a white LED that initially has a chromaticity within the definition of Aviation White may, over time, color shift so that it is no longer in compliance with applicable regulations.
The present invention comprises a dual-color ACL having a first set of LEDs that emit a substantially white beam of light and a second set of LEDs that emit a substantially red beam of light. According to an illustrative embodiment, the ACL is capable of being operated in two modes. In one mode, the red LEDs are excited by themselves so that the ACL produces a red beam of light having a chromaticity within the definition of Aviation Red and a luminous output of 150-250 cd. In the second mode, the white LEDs and the red LEDs are excited simultaneously to produce a white beam of light having a chromaticity within the definition of Aviation White and a luminous output of 1500-2500 cd. Operating the red LEDs in the white mode has two synergistic effects. First, the red LEDs augment the luminous output of the white LEDs so that fewer white LEDs are required, thus saving cost and space. Second, the red LEDs shift the chromaticity of total light output toward the red region. This has the effect of compensating for the tendency of the white LEDs to become greener with age. In one embodiment, the white LEDs, when new, produce light with a chromaticity that is outside the definition of Aviation White but, when color-mixed with the red LEDs, the total light output is within the definition of Aviation White. Utilizing LEDs that are arranged for color mixing also has the advantage of requiring only a single optical system as opposed to the two optical systems required by the prior art ACLs.
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which:
The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.
With reference to
With reference to
In the illustrative embodiment of
y≦0.335; and
z≦0.002.
Suitable red LEDs include the Osram Oslon LA CP7P (x=0.685, y=0.315) manufactured by Osram Opto Semiconductors GmbH of Regensberg, Germany; the CREE CLM2-REW (x=0.699, y=0.301) manufactured by Cree, Inc. of Durham, N.C., USA or other suitable high output red LED. (As used herein all x, y coordinates refer to the coordinates on the 1931 C.I.E. Chromaticity Diagram.)
The white LEDs may be any conventional white LED having sufficient luminous output. For reasons that will be discussed more fully hereinafter, however, the chromaticity of the white LEDs may be, but is not necessarily within the definition of Aviation White, which is defined by the following formula on the 1931 C.I.E. Chromaticity Diagram:
x≧0.300 and x≦0.540;
y≧(x−0.040; or y0−0.010),
whichever is the smaller; and
y≦(x+0.020) and y≦0.636−0.400x;
Where y0 is the y coordinate of the Planckian radiator for the value of x considered.
Suitable white LEDs include the Nichia NCSW119A (bin cl, x=0.330, y=0.339) manufactured by Nichia Corporation of Tokushima, Japan, the CREE XP-E cool white (x=0.311, y=0.322) manufactured by Cree, Inc. of Durham, N.C., USA or other suitable high output white LED.
As shown in Table 1 below, and with reference to
In a second illustrative embodiment, ACL 30 comprises an array of 41 white LEDs and nine red LEDs. When operated in the red mode, the nine red LEDs produce a luminous output of 450 lm with a center wavelength of 620 nm (which corresponds to a chromaticity of (x=0.680, y=0.320)). This light output is within the definition of Aviation Red as shown in
Additional embodiments increase the ratio of red LEDs to white LEDs and the total number of LEDs in the array as shown in Table 1. Typically the red LEDs will have a combined luminous output of less than 500 lm while the luminous output in the white mode (red and white LEDs) will have an output of at least 1000 lm. Ordinarily at least 1% of the combined light output is from the red LEDs however, 4-5%, 10%, 20% or more is possible depending on the application and the amount of red-shift desired.
As noted hereinbefore, as white LEDs age and/or are exposed to elevated temperatures, the phosphor deteriorates. This causes a color-shift in the chromaticity of the LEDs. For example, as shown at reference 60a, an XPG white LED operated at 60° C. color-shifts from a nominal chromaticity of (x=0.2890, y=0.2868) which is just outside of the definition of Aviation White to a chromaticity of (x=0.3230, y=0.3533) after 3800 hours of operation, which is well outside the definition of Aviation White as shown in
Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although in the illustrative embodiment, the red LEDs were selected to have a center wavelength of 615-620 nm, other Aviation Red LEDs having a center wavelength of greater than 620 nm or less than 615 nm may be utilized if a greater impact on the y-coordinate of the combined light output is desired. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, references to direction such as “up” or “down” are intend to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “substantially” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater.
