BACKGROUND
The present disclosure relates to optical systems for use in conjunction with flood and area lights for work site illumination and emergency vehicles.
Halogen, metal halide, mercury vapor, sodium vapor, arc lamps and other light sources have been employed in floodlights. Floodlights typically employ a weather-resistant, hermetic housing surrounding the light source. The light source is typically positioned in front of a reflector and behind a lens, each of which are configured to redirect light from the light source into a large area diverging beam of light. Traditional floodlights are typically mounted so that the direction of the light beam can be adjusted with respect to the horizontal, allowing the floodlight to illuminate areas above or below the height of the light. The floodlight support may also permit rotation of the light.
When floodlights are employed in conjunction with emergency response vehicles such as fire trucks, ambulances or rescue vehicles, they may be mounted to a pole which allows the elevation and orientation of the floodlight to vary with respect to the vehicle. Alternatively, floodlights may be mounted to the top front corner of the cab (so called “brow lights”), or the floodlights are mounted in an enclosure secured to a vertical side or rear face of the vehicle body. It is frequently desirable for the floodlight to illuminate an area of the ground surrounding the vehicle. In such cases, floodlights are typically directed downward to produce the desired illumination pattern.
While prior art floodlights have been suitable for their intended purpose, prior art light sources suffer from excessive energy consumption and relatively short life spans. Light emitting diode (LED) light sources are now commercially available with sufficient intensity of white light to make them practical as an alternative light source for flood and area lighting. The semiconductor chip or die of an LED is typically packaged on a heat-conducting base which supports electrical connections to the die and incorporates some form of lens over the die to shape light emission from the LED. Such packages including a base with electrical connections and thermal pathway, die and optic are typically referred to as an LED lamp. Generally speaking, LED lamps emit light to one side of a plane including the light emitting die and are therefore considered “directional” light sources. The light emission pattern of an LED is typically measured and described with respect to an optical axis projecting from the die of the LED and perpendicular to the plane including the die. A hemispherical (lambertian) pattern of light emission can be described as having an angular distribution of two pi steradians.
Although the total optical energy emitted from an LED lamp continues to steadily improve, it is still typically necessary to combine several LED lamps to obtain the optical energy necessary for a given illumination pattern. Optical systems are employed to integrate the optical energy from several LED lamps into a coherent illumination pattern suitable for a particular task. Optical systems utilize optical elements to redirect light emitted from the several LED lamps. Optical elements include components capable of interacting with optical energy and can include devices such as, but not limited to, filters, reflectors, refractors, lenses, etc. Light being manipulated by optical elements typically experiences some form of loss from scatter, absorption, or reflection. Thus, for example, optical energy interacting with a lens will scatter a percentage of the optical energy at each lens surface with the remainder of the optical energy passing through the lens. A typical aluminized reflector is between 92 and 95% efficient in redirecting optical energy incident upon it, with the remainder being scattered or absorbed. Optical efficiency is the ratio of total optical energy that reaches the desired target area with respect to the total optical energy produced by the light source.
In a typical prior art optical system, the optical elements are arranged symmetrically with respect to an optical axis of the light source, such as a circular parabolic aluminized reflector (PAR), a circular Fresnel lens or the like. Other prior art optical systems may exhibit elongated symmetry with respect to a longitudinal axis and/or plane bisecting the light. Elongated symmetry is commonly associated with elongated lamp formats used in some quartz halogen, fluorescent or metal halide light sources.
SUMMARY
An objective of the disclosed asymmetrical optical system is to efficiently redirect light from the plurality of LEDs into a desired illumination pattern. The disclosed asymmetrical optical system employs optical elements only where necessary to redirect light from the LEDs into the desired illumination pattern. Where light from the LEDs is emitted in a direction compatible with the desired illumination pattern, the light is allowed to exit the asymmetrical optical system without redirection by an optical element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view through a floodlight employing two alternative embodiments of an asymmetrical optical system according to the present disclosure;
FIG. 2 is a sectional view through the floodlight of FIG. 1, showing redirection of light emanating from LED lamps by reflecting surfaces in each of the disclosed asymmetrical optical systems;
FIG. 3 is a sectional view through the floodlight of FIG. 1, showing redirection of light emanating from LED lamps by lenses in each of the disclosed asymmetrical optical systems;
FIG. 4 is a sectional view through the floodlight of FIG. 1 showing redirection of light emanating from LED lamps by reflecting surfaces and lenses in each of the disclosed asymmetrical optical systems;
FIG. 5 is a partial sectional view, shown in perspective, of the reflector and lenses of the asymmetrical optical systems of the floodlight of FIG. 1;
FIG. 6 is a side sectional view through the reflector, lenses and PC boards of the floodlight of FIG. 1;
FIG. 7 is a front view of the reflector and PC boards of the floodlight of FIG. 1 with the lenses removed; and
FIG. 8 is a front view of the reflector, PC boards and lenses of the floodlight of FIG. 1;
FIG. 9 is a front elevation view of an alternative embodiment of an asymmetrical optical system according to the disclosure;
FIGS. 10 and 11 are side sectional views through the asymmetrical optical system of FIG. 9, taken along line 10-10 thereof;
FIG. 12 is a front perspective view of the asymmetrical optical system of FIG. 9 from above; and
FIG. 13 is an enlarged, partial front perspective view of the asymmetrical optical system of FIG. 9 taken from below.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
As shown in FIGS. 1-8, two disclosed embodiments of an asymmetrical optical system 10a, 10b are incorporated into a floodlight 12 intended for use in combination with emergency response vehicles or as a work area light, though the disclosed optical system is not limited to these uses. The disclosed asymmetrical optical systems 10a, 10b employ optical elements that are not symmetrical with respect to an optical axis AO of the LED lamps 18 or a longitudinal axis AL or plane P2 bisecting each asymmetrical optical system 10a, 10b.
With reference to FIGS. 1-4, the disclosed floodlight 12 includes a heat sink 14 which also serves as the rear portion of the housing for the floodlight 12. The heat sink 14 may be extruded, molded or cast from heat conductive material, typically aluminum and provides support for PC boards 16. A die cast aluminum heat sink is compatible with the disclosed embodiments. The heat sink 14 includes a finned outside surface, which provides expanded surface area to for shedding heat by radiation and convection. PC boards 16 carrying a plurality of LED lamps 18 are secured in thermally conductive relation to the heat sink 14 to provide a short, robust thermal pathway to remove heat energy generated by the LED lamps 18. In the disclosed floodlight 12, the plurality of LED lamps 18 are arranged in linear rows (linear arrays 19 best seen in FIG. 7) with the light emitting dies of each LED lamp 18 in each row being aligned along a longitudinal axis AL. This configuration places the optical axes AO of the plurality of LED lamps 18 in a plane P2 perpendicular to a planar surface P1 defined by the PC boards 16. In this configuration, light is emitted from the LED lamps 18 in overlapping hemispherical (lambertian) patterns directed away from the planar surface P1 defined by the PC boards 16.
The disclosed floodlight 12 is of a rectangular configuration and employs two alternatively configured asymmetrical optical systems 10a, 10b. The two asymmetrical optical systems 10a, 10b in the disclosed floodlight 12 share several common optical elements and relationships, but also differ from each other in material respects. Each of the asymmetrical optical systems 10a, 10b includes a linear array 19 of LED lamps 18 arranged to emit light on a first side of a first plane P1. A second plane P2 includes the optical axes AO of the LED lamps 18 and is perpendicular to the first plane P1. The second plane P2 passes through a longitudinal axis AL connecting the light emitting dies of the LED lamps 18 and bisects each asymmetrical optical system 10a, 10b into upper 24a, 24b and lower portions 25a, 25b, respectively.
Each of the asymmetrical optical systems 10a, 10b include first and second reflecting surfaces 20a, 20b; 22a, 22b originating at the first plane P1 and extending away from the first plane P1 and diverging with respect to the second plane P2. With respect to asymmetrical optical system 10a (shown at the top in FIGS. 1-8), the first and second reflecting surfaces 20a, 22a are asymmetrical with respect to each other, e.g., the reflecting surfaces are not mirror images of each other. The first and second reflecting surfaces 20a, 22a are separated by and spaced apart from the second plane P2 to form a pair of longitudinally extending reflecting surfaces on either side of the longitudinal axis AL of the linear array 19 of LED lamps 18. In asymmetrical optical system 10a, the first reflecting surface 20a is arranged to redirect light emitted from the LED lamps 18 at relatively large angles with respect to the second plane P2. In asymmetrical optical system 10a, the first reflecting surface 20a is arranged to redirect light emitted at angles greater than approximately 30° with respect to said second plane P2 as best seen in FIG. 1. Light emitted from the LED lamps 18 having this trajectory may also be referred to as “wide-angle” light. In the disclosed asymmetrical optical systems 10a, 10b, the first and second reflecting surfaces 20a, 20b; 22a, 22b are generally parabolic and may be defined by a parabolic equation having a focus generally coincident with the longitudinal focal axis AL of the linear array 19 of LED lamps 18.
The parabola or parabolic curve is projected along the longitudinal axis AL passing through the LED dies to form a generally concave reflecting surface as best illustrated in FIGS. 1-6. The term “parabolic” as used in this disclosure means “resembling, relating to or generated or directed by, a parabola.” Thus, parabolic is not intended to refer only to surfaces or curves strictly defined by a parabolic equation, but is also intended to encompass variations of curves or surfaces defined by a parabolic equation such as those described and claimed herein. A true parabolic trough would tend to collimate light emitted from the linear array 19 of LED lamps 18 with respect to the plane P2 bisecting each asymmetrical optical system. The word “collimate” as used in this disclosure means “to redirect the light into a direction generally parallel with” a designated axis, plane or direction. Light may be considered collimated when its direction is within 5° of parallel with the designated axis, plane or direction and is not restricted to trajectories exactly parallel with the designated axis, plane or direction.
A collimated light emission pattern (such as a narrow beam) is not desirable for a floodlight and the disclosed asymmetrical optical systems 10a, 10b modify the optical elements to provide a divergent light emission pattern better suited to area illumination. For example, reflecting surfaces 20a and 22b in the disclosed floodlight 12 include longitudinally extending convex ribs 23 which serve to spread light with respect to the second plane P2 as best shown in FIG. 2. The surface of each rib 23 begins and ends on the parabolic curve which generally defines the reflecting surface 20a, 22b and each rib 23 has a center of curvature outside of the parabolic curve. Thus, the several longitudinally extending ribs 23 (segments) closely track a curve defined by a parabolic equation to form a parabolic reflecting surface. As shown in FIGS. 2 and 4, the general effect of such a reflecting surface 20a, 22b is to redirect wide-angle light emitted from the LED over a range of emitted angles greater than approximately ˜30°-˜90° with respect to the second plane P2 into a range of reflected angles (less than ˜20°) with respect to said second plane P2, where each angle in the range of reflected angles is less than any angle in the range of emitted angles. More specifically, the reflecting surfaces 20a, 22b are configured to produce a range of reflected angles with respect to the second plane P2 that is less than ˜20° to either side of the second plane P2 or more preferably less than or equal to approximately 10° to either side of the second plane P2. This configuration brings light into the desired light emission pattern for the floodlight and spreads the available light over a large area to produce an illumination pattern having relatively uniform brightness. This reflector configuration uses the reflecting surface to redirect light into the desired pattern, rather than collimating the light and then using a lens to spread the light.
Light is emitted from each LED lamp 18 in a divergent hemispherical pattern such that little or no light is emitted at an angular orientation that is convergent with the second plane P2. As shown in FIGS. 2-4, the disclosed asymmetrical optical systems 10a, 10b redirect at least a portion of the divergent light emitted from each LED lamp 18 into an angular orientation that converges with and passes through the second plane P2. For example, wide angle light emitted from LED lamps 18 in (upper) asymmetrical optical system 10a in an upward direction (according to the orientation of the Figures) at an angular orientation of greater than 30° with respect to the second plane is redirected by the corresponding reflecting surface 20a into a range of reflected angles, at least some of which give the light a direction (trajectory) which converges with and passes through the second plane P2 to contribute to the illumination pattern below the second plane P2 in the orientation shown in FIG. 2. The reverse is true of the opposite (lower) reflecting surface 22b of asymmetrical optical system 10b, which reorients wide-angle light from the LED lamps 18 into a direction that converges upwardly with and passes through the second plane P2 to contribute to the illumination pattern above the second plane P2 in the orientation of FIG. 2. Reflecting surfaces 20a and 22b are mirror images of each other in the disclosed asymmetrical optical systems, but this is not required.
Each asymmetrical optical system 10a, 10b also includes a lens optical element 30 arranged primarily to one side of the second plane P2. As shown in FIGS. 1-6 and 8, the lens optical element 30 has a substantially constant sectional configuration and extends the length of the linear array 19 of LED lamps 18. The lens optical element 30 is primarily defined by a light entry surface 32 and a light emission surface 34. The light entry surface 32 and light emission surface 34 are constructed to cooperatively refract light incident upon the lens optical element 30 into a direction contributing to the desired illumination pattern for the floodlight as shown in FIGS. 3 and 4. In the case of the disclosed floodlight 12, the desired illumination pattern is a diverging pattern in which a majority of the optical energy of each linear array 19 of LED lamps 18 is emitted at an angular orientation below the second plane P2 (with reference to the orientation of FIGS. 1-8). This illumination pattern is particularly useful in a flood or area light as it illuminates an area immediately beneath the light or adjacent the side of a vehicle equipped with the light, without requiring that the light be aimed in a dramatic downward orientation. In the disclosed lens optical element 30, the light entry surface 32 is an elongated curved surface convex in a direction facing the LED lamps 18. The light entry surface 32 is configured to at least partially collimate light entering the lens optical element, where “collimate” means redirect the light into an angular orientation substantially parallel with the second plane P2. “Substantially collimated” as used herein means “close to parallel with” and should be interpreted to encompass angular orientations within about ±5° of parallel. As shown in FIG. 3, the light emission surface 34 of the disclosed lens optical element 30 is a planar surface having an orientation which refracts light leaving the lens optical element 30 into a range of angles from parallel (0°) with the second plane P2 to angles converging with and passing through the second plane P2. This lens optical element 30 configuration redirects light emitted on a trajectory divergent from and above the second plane P2 of each asymmetrical optical system 10a, 10b to a direction contributing to the illumination pattern below the second plane P2 of each asymmetrical optical system 10a, 10b according to the orientation shown in FIGS. 1-8.
The disclosed lens optical element 30 is asymmetrical with respect to the second plane P2 and the optical axes AO of the LEDs 18. Specifically, the disclosed lens optical element 30 is positioned primarily to one side (above) of the second plane P2, although other lens configurations and positions are compatible with the disclosed embodiments. The lens optical element 30 is closer to one of the reflecting surfaces 20a, 20b of the respective asymmetrical optical systems 10a, 10b than to the other of the reflecting surfaces 22a, 22b. The position of the lens optical element 30 defines a gap 36 between the lens optical element 30 and the lower reflecting surface 22a, 22b where light emitted from the LEDs 18 exits each asymmetrical optical system 10a, 10b without redirection by either the lens optical element 30 or either reflector. It will be noted that light from the LEDs 18 which is permitted to leave each asymmetrical optical system 10a, 10b without redirection has an emitted angular direction where the light contributes to the desired illumination pattern of the floodlight.
The reflecting surfaces 20a, 22a; 20b, 22b are not symmetrical with respect to each other as shown in FIGS. 1-8. In the upper asymmetrical optical system 10a, the top reflecting surface 20a projects away from the first plane P1 a much greater distance than the truncated lower reflecting surface 22a. This configuration permits light from the LEDs 18 having an angular orientation of between 0° (parallel to P2) and approximately 62° below the second plane P2 to exit the upper asymmetrical optical system 10a without redirection by either the lens optical element 30 or either reflecting surface 20a, 22a. Reflecting surface 22a of the upper asymmetrical optical system 10a includes two longitudinally extending planar facets 25 where either longitudinal edge of each facet 25 touches on a parabolic curve. This configuration redirects wide-angle light (emitted at angles of between ˜90°-˜60° with respect to the second plane P2) incident upon the lower reflecting surface 22a into a range of reflected angles from about 10° divergent from said second plane to about 10° convergent with respect to the second plane as best seen in FIG. 2.
To complete the reflector of the disclosed floodlight 12, a planar surface 28 connects the outer edge of the upper asymmetrical optical system 10a lower reflecting surface 22a with the outer edge of the lower asymmetrical optical system 10b upper reflecting surface 20b. Surface 28 is aluminized to reflect light incident upon it, but this surface does not form an operational component of either asymmetrical optical system 10a, 10b.
It will be observed that the upper and lower asymmetrical optical systems 10a, 10b differ with respect to each other. The upper asymmetrical optical system 10a employs a truncated lower reflecting surface 22a comprised of planar longitudinally extending facets 25. The facets begin and end on a parabolic curve and form a parabolic reflecting surface 22a. The lower asymmetrical optical system 10b employs a lower reflecting surface 22b that is a mirror image of the upper asymmetrical optical system 10a upper reflecting surface 20a.
The lower asymmetrical optical system 10b upper reflecting surface 20b is a parabolic surface defined by projection of a parabolic curve along the longitudinal axis AL passing through the LED dies of the lower asymmetrical optical system 10b linear array 19 of LED lamps 18. The parabolic curve used to define reflecting surface 20b has a shorter focal length than the curves employed to define the other reflecting surfaces 20a, 22a, 22b (measured between the focus and the vertex of the parabolic curve). The focal length of the curve used for reflecting surface 20b is approximately one-half of the focal length (0.05″ vs. 0.1″) of the curve used to define the other reflecting surfaces 20a, 22a, 22b. This surface construction redirects light emitted from the lower linear array 19 of LED lamps 18 in asymmetrical optical system 10b above the second plane P2 and divergent from the second plane P2 into a direction substantially collimated with respect to the second plane as shown in FIG. 4. As shown in FIG. 4, some light redirected by reflecting surfaces 20a and 20b is collimated (substantially parallel with plane P2) and passes through lens optical elements 30. The lens optical element 30 redirects this collimated light into an orientation which converges with and passes (downwardly) through the second plane P2. This light contributes to the desired illumination pattern of the flood light 12.
Each asymmetrical optical system 10a, 10b is asymmetrical with respect to a second plane P2 which includes the optical axes AO of the LED lamps 18 in the respective linear arrays 19 of LED lamps. The illumination pattern generated by the flood light 12 is asymmetrical with respect to a third plane P3 bisecting the flood light 12.
An alternative asymmetrical optical system 100 is illustrated in FIGS. 9-13. This alternative LED light and optical system is intended for mounting to a vertical surface of an emergency vehicle (not shown) for the purpose of illuminating the area around the vehicle during use at the site of an emergency. The low profile configuration of this optical system is intended to avoid the need to cut into the side panels of an emergency vehicle when mounting the light. In this embodiment, light from a linear array of LEDs 18 is managed by a first reflecting surface 120, a longitudinally extending lens 130 and a segmented second reflecting surface 140a, 140b, 140c, 140d.
The linear array of LEDs 18 is mounted to a printed circuit board 160 having thermal management properties as is known in the art. A reflector 150 supports reflecting surfaces 120 and 140(a-d) and defines a gap 152 for the arrays of LEDs 18. FIG. 9 illustrates a longitudinally extended optical arrangement with four identical segments 110, with each segment including a linear array of 12 LEDs 18. Since the segments are identical, only one segment 110 will be described in detail. Each LED 18 supports a die 18a beneath a lens and on top of a heat conducting slug 18b. The LED dies 18a from which light is emitted are arranged in a row and supported so the dies 18a fall in a first plane P1. Each LED has an optical axis AO projecting through the center of the die 18a and perpendicular to the first plane P1. A second plane P2 includes the optical axes of each of the LEDs 18, and also includes a linear focal axis AL which extends through the dies 18a. Thus, the linear focal axis AL defines an intersection between plane P1 and perpendicular plane P2.
Each of the reflecting surfaces 120, 140(a-d) and lens 130 are configured to direct light emitted from the LEDs 18 in a downward directed, flood light pattern. With reference to FIGS. 10 and 11, those skilled in the art will recognize that a portion of the light from each LED 18 is incident upon first reflecting surface 120, a portion is incident upon the lens 130, a portion is incident upon segmented reflecting surface 140(a-d) and a significant portion is allowed to exit the optical assembly without being redirected at all. The reflecting surfaces 120, 140(a-d) and the lens have substantially constant sectional configurations and the shapes shown in FIGS. 10 and 11 are projected along the linear focal axis AL passing through the LEDs 18 to define the surfaces shown. First reflecting surface 120 is a modified parabolic curve having an axis canted at an angle 122 of approximately 5° downward from plane P2. Reflecting surface 120 is faceted, comprising a plurality of linear segments 120a, 120b, 120c, etc. originating and terminating at the parabola defining the reflecting surface 120. This faceted configuration spreads light into a more uniform flood illumination pattern, while the canted, modified parabolic surface directs light generally downward with respect to plane P2. Reflecting surface 120 is not limited to the specific disclosed configuration and other similar surface shapes may be compatible with the disclosed optical system.
As best shown in FIG. 11 each of the reflector segments 140 (a-d) is also defined by a parabolic curve having an axis canted at an angle 122 of approximately 5° downward with respect to plane P2. Reflector segments 140(a-d) are spaced apart from plane P2 and much farther away from the linear arrays of LEDs 18. Reflector segments 140(a-d) are arranged to reflect light emitted from said LEDs 18 at angles greater than approximately 80° relative to the optical axis AO of the LEDs. This “wide angle” light is re-directed by the reflector segments 140(a-d) into a range of much smaller angles with respect to the plane P2 and the optical axes AO of the LEDs 18. Wide angle light incident upon the reflector segments 140(a-d) is re-directed into a forward emission pattern and at least partially fills the lower portion of the optical assembly 100.
Lens 130 has a substantially constant sectional shape best seen in FIG. 11, except were modified for mounting hardware. Lens 130 is defined by a light entry surface 132, a light emission surface 134 and a side cut 136. Light entry surface 132 is an aspheric surface configured to partially re-direct divergent light entering the lens toward plane P2, e.g., reduce the angle at which the light is diverging from plane P2. Light emission surface 134 is another aspheric surface configured to refract light leaving the lens 130 into a range of angles including angles convergent with and passing through the second plane P2. Light entry and light emission surfaces 132, 134 are not configured to collimate light passing through the lens 130, but instead are configured to re-direct light in a slightly downward, spread pattern suitable for flood lighting adjacent an emergency vehicle. Side cut 136 is a planar surface which is positioned to allow most of the light to one side of plan P2 to exit the optical assembly 100 without passing through the lens 130. Side cut 136 is canted at 5° with respect to the second plane P2 and offset from plane P2 by a distance approximately equal to ½ of the width of the LED die 18a. This configuration is intended to place the light entry surface 132 in the path of light emitted from each LED 18 along the optical axis AO. An upper boundary of the lens 130 is arranged to allow light incident upon the first reflecting surface 120 to pass the lens 130 and may include a bevel or angled surface for this purpose.
Light emitted from the LEDs 18 and having a trajectory above plane P2 is handled by the first reflecting surface 120 and lens 130, being re-directed into a slightly diffuse, slightly downward directed flood light emission pattern. A substantial portion of light emitted from the array of LEDs 18 to the opposite side of plane P2 (away from the first reflecting surface/below plane P2) is allowed to exit the optical assembly 100 without re-direction. Light emitted from the array of LEDs 18 within angle 124 passes by the lens side cut 136 and is not incident upon reflector segments 140(a-d). Lens 130 is intersected by plane P2 but is asymmetrical with respect to this plane, a majority of the lens 130 being between plane P2 and the first reflecting surface 120. Light having this trajectory is already emitted in a direction useful for the intended flood light pattern and is most efficiently allowed to exit the optical assembly without the losses associated with reflection or refraction.
The disclosed optical systems employing a reflector and lens optical elements may alternatively be constructed employing internal reflecting surfaces of a longitudinally extending solid of optically transmissive material as is known in the art.
While the invention has been described in terms of disclosed embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and the scope of the appended claims.
Patent Grant
9388961
