The present invention relates to high intensity lights, and more specifically to an LED based high intensity obstruction light.
High intensity lights are needed for applications such as navigation beacons. For example, navigation lamps for aviation must be capable of meeting the 2,000 candela (cd) requirements for the U.S. Federal Aviation Authority (FAA) L864 standard and the International Civil Aviation Organization (ICAO) Medium Intensity Type B and Type C Navigation Lights standard. In the past such navigation lamps have used conventional strobe lights. However, strobe lights are energy and maintenance intensive. Recently, lamps have been fabricated using light emitting diodes (“LED”). LEDs create unique requirements in order to be commercially viable in terms of size, weight, price, and cost of ownership compared to conventional strobe lights, but are more energy efficient and require less maintenance.
The FAA and ICAO regulations set the following stringent requirements for beam characteristics at all angles of rotation (azimuth). Lights must have effective (time-averaged) intensity greater than 750 candela (cd) over a 3° range of tilt (elevation). Lights must also have peak effective intensity of 1,500-2,500 cd and effective intensity at −1° elevation of 750-1,125 cd for the ICAO only. In particular, the ICAO standard sets a very narrow “window” of beam characteristics at −1° of elevation which must be met by beams at all angles of rotation (azimuth).
In order to achieve the total light intensity required for an FAA or ICAO compliant light using LEDs, it is necessary to use a large number of LED based light sources. An example known high intensity obstruction light has three circular rows of LEDs and total internal reflection (TIR) lenses to achieve the required total illuminance and light beam uniformity. The number of rows increases the total height of the light engine, requiring a correspondingly taller enclosure, thereby increasing the total weight, height, and cost of the final obstruction light product.
However, it is difficult to create a beam with the desired intensity pattern when directing large numbers of LED light sources into few reflectors. Furthermore, smaller and therefore more numerous reflectors are needed to conform to overall size restrictions. These constraints all result in a design with a large number of optical elements comprised of individual LEDs and small reflectors. A final challenge is alignment of the multiple optical elements such that their outputs combine to form a beam which is uniform at all angles of azimuth.
Currently, available LED lamps simply stack multiple of optical elements symmetrically, as well as using complex TIR reflectors and multiple LEDs per reflector. Such complex reflectors require a solid plastic part with precise optical surfaces which is costly to mold. While compliant, such lamps require more than an optimal number of LEDs and thus are complex and expensive. A large number of LEDs requires a corresponding number of TIR lenses and LED circuit boards, all of which increase the cost of the light engine. The number of LEDs increases the electrical power required and the total heat which must be dissipated. Finally, the solid nature of the TIR lenses and the number of TIR lenses contribute to the total weight of the light engine, which can make installation of the final obstruction light product more difficult.
Thus there is a need for an efficient LED based lamp that meets FAA and ICAO standards. There is also a need for an LED lamp that allows the use of relatively smaller reflectors. There is a further need for an LED lamp that provides uniform light output.
One example relates to a high intensity light having a first circular lighting array having a plurality of reflectors and light emitting diodes. A second circular lighting array is mounted on the first circular lighting array. The second circular lighting array has a second plurality of reflectors and light emitting diodes. Each reflector includes a reflective surface having a symmetrical vertical cross section and a different symmetrical horizontal cross section to create a uniform beam reflecting from a corresponding LED at horizontal angles relative to the reflective surface and a narrow beam in vertical angles relative to the reflective surface.
Another example is an optical assembly for producing a uniform light beam reflected from a corresponding light source at horizontal angles and a narrow beam in vertical angles. The optical assembly has a support member mounted vertically having an exterior surface. A light emitting diode is mounted on the exterior surface of the support member. A reflector is mounted on the exterior surface of the base member. The reflector has a reflective surface including segments generated as parabolic curves joined to form a contiguous surface. The reflective surface has a vertical symmetry and a different horizontal symmetry.
Another example is an aircraft warning lamp having a first circular lighting array having a first plurality of optical elements emitting light at all horizontal angles and a narrow beam in vertical angles. A second circular lighting array has a second plurality of optical elements emitting light at horizontal angles and a narrow beam in vertical angles. The second plurality of optical elements is offset from the first plurality of optical elements. Each of the optical elements includes a light emitting diode and a reflector. The reflector has a reflective surface having a symmetrical vertical cross section and a different symmetrical horizontal cross section to create a uniform beam reflecting from a corresponding light emitting diode at horizontal angles relative to the reflective surface and a narrow beam in vertical angles relative to the reflective surface.
Additional aspects will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below.
While these examples are susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail preferred examples with the understanding that the present disclosure is to be considered as an exemplification and is not intended to limit the broad aspect to the embodiments illustrated.
In the preferred embodiment, there are eleven optical elements 110 arrayed circumferentially in each of the circular lighting arrays 112 and 114, so the optical elements 110 are spaced at equal angular intervals of 360/11=32.7°. The optical elements 110 of the second circular light array 114 achieve the desired total intensity and to fill in the “gaps” (i.e., regions of low light intensity) from the first circular lighting array 112. In this example, the two circular light arrays 112 and 114 together form two rows with eleven optical elements 110 per row. The offset between the optical elements 110 in the two rows of the respective two circular light arrays 112 and 114 is 360/22=16.4°
In this example, the individual optical elements 110 have a pattern of beam intensity versus azimuth angle, which when combined with light from adjacent optical elements 110, produces total beam intensity with minimum ripple. Reflector designs could be further optimized so that the summation of intensities has even less ripple variation than illustrated here.
The circular lighting arrays 112 and 114 are constructed from vertical heat sinks 116 mounted radially on the base 102 in
Each of the optical elements 110 have a circuit board 130 mounting an LED 132 with a tulip-shaped reflector 134. As will be detailed below, the reflectors 134 have multiple reflective surfaces 150 and are constructed of molded plastic such as polycarbonate. In this example, the multiple reflective surfaces 150 of the reflectors 134 are coated with a reflective material such as vacuum deposited aluminum with suitable clear protective overcoat material such as SiO2 or UV-cured polymer.
The LEDs 132 are preferably commercially available “high brightness” light emitting diodes, preferably red, with color chromaticity meeting ICAO and FAA requirements in this example, but other LED types may be used for other applications. The LEDs 132 are attached to the circuit board 130 which, in this example, is a thermally conductive printed circuit board (PCB), preferably having a metal core of aluminum, a thin dielectric layer, and a copper layer defining the electrical pathways. The LEDs 132 are preferably attached using solder, eutectic bonding, or thermally conductive adhesive.
The printed circuit board 130 has wiring attachment points 138 provided for supplying wiring to the electrical components of the printed circuit board 130. The printed circuit board 130 is attached to the heat sink 116 with screws 142 that fix the angular and vertical position of the printed circuit board 130 and corresponding optical element 110 relative to the heat sink 116. The reflector 134 has additional physical registration features such as tabs which allow the reflector 134 to be aligned or centered optically with the LED 132. In this example, mounting screws 142 are inserted through holes 140 in the reflector 134 and the printed circuit board 130 to fix the reflector 134 and the printed circuit board 130 to the heat sink 116.
The heat sink 116 serves to mount and align the circuit board 130 and corresponding LEDs 132 and reflectors 134 of the optical elements 110. The heat sink 116 conducts heat from the LEDs 132 and dissipates the conducted heat through the base 102 shown in
Heat is removed from the LEDs 132 via conduction through the printed circuit boards 130, through conductive grease or adhesive to the heat sink 116. A portion of the heat is conducted through the heat sink to the lower base 102, from which the heat is transferred to the ambient air. Heat may also be transferred from the heat sink integral fins 122 by convection.
As shown in
It is desirable that the beam pattern of light intensity versus elevation is closely matched at all angles of azimuth so that all beams will lie within the allowable “windows” of the ICAO and FAA requirements for this example. Another way of stating this is that a plot of intensity vs. azimuth angle at a fixed angle of elevation should show minimal variation, or “ripple.” “Ripple” is defined as the peak to peak variation in intensity relative to the average intensity at all angles of azimuth.
Minimum ripple has several advantages, it is more feasible to meet the FAA and ICAO requirements and it allows reducing the drive current and/or the number of LEDs needed to achieve minimum intensity at all points.
As shown in
The optical elements 110 could also be modified with other reflector geometry. Further, side-emitting LEDs directed back into a reflector could be used for the optical elements 110. Other reflector designs could be used. For example, a reflector which does not have a horizontal plane of symmetry, if the desired beam pattern were not symmetrical in elevation above and below the horizon (zero elevation) could be used. Alternatively, a reflector in which the horizontal plane of symmetry is not perpendicular to the vertically oriented substrate, if the desired beam pattern is to be directed preferentially above or below the horizon (zero elevation) could be used. The reflectors could also be reflectors combined in groups via molding two or more reflectors. Also, multiple LEDs may be used for each reflector. Staggered TIR optics could be used for the reflectors. Different numbers of LEDs per circular array and different numbers of circular arrays may also be used. An equivalent linear light with similar staggered sources could be used. An electrical control system with adjustable current for each LED or group of LEDs could be used to further reduce variations in beam intensity and uniformity.
Other example applications of the above mentioned concepts include marine navigation lights (e.g., 10 and 15 nautical miles) which require similar beam patterns, other obstruction lights, such as the FAA/ICAO 20,000 cd light, and any other lighting application which similarly requires an energy-efficient, cost-effective LED light with well defined beam pattern. Further, the high intensity optical elements of the high intensity light 100 in
Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.
This application claims priority from U.S. Provisional Application No. 61/102,564 filed on Oct. 3, 2008 to the same inventors. That application is incorporated by reference in its entirety.
Number | Date | Country | |
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61102546 | Oct 2008 | US |