Patent Application
20150085479
The present disclosure relates generally to warning light devices, and more particularly to optical configurations for producing integrated directional light from a LED light sources.
While not limited thereto in its utility, the novel technology to be described below is particularly well suited for use in combination with light emitting diodes (LED's) and, especially, for use in warning and signaling lights.
Commercially available LED's have characteristic spatial radiation patterns with respect to an optical axis which passes through the light emitting die. A common characteristic of LED radiation patterns is that light is emitted in a pattern surrounding the optical axis from one side of an imaginary plane containing the light emitting die, the optical axis being oriented perpendicular to this plane and emanating from a center of the die. Typically, the light generated by an LED is radiated within a hemisphere centered on the optical axis, with a majority of the light emitted at angles close to the optical axis of the LED. Although the quantity of light emitted typically declines as the angle relative to the optical axis of the LED increases, light emitted at angles greater than approximately 45° represents a significant portion of the overall light output of the LED. The distribution of light radiation within this hemisphere is determined by the shape and optical properties of the lens (if any) covering the light emitting die of the LED. Thus, LED's can be described as “directional” light sources, since all of the light they generate is emitted from one side of the device, with the other side dedicated to a support that provides electrical power to the LED and conducts heat away from the die.
When designing light sources for a particular purpose, it is important to maximize efficiency by ensuring that substantially all of the generated light is arranged in a pattern or field of illumination dictated by the end use of the device into which the light source is incorporated. The somewhat limited overall light output of individual LEDs frequently necessitates that several discrete LED components be cooperatively employed to meet a particular photometric requirement. Use of arrays of LEDs and their directional emission pattern present particular challenges to the designer of warning and signaling lights. Employing LEDs in compact arrays additionally imposes cooling, i.e., “heat sinking”, requirements which may not be present in the case of prior art warning and signal light design.
The present disclosure includes an optical assembly configured to produce an integrated light emission pattern relative to a first plane with limited spread in imaginary planes perpendicular to the first plane. For purposes of this application, light emitted from an LED can be described as “narrow angle” light emitted at an angle of less than about 45° from the optical axis and “wide angle” light emitted at an angle of more than about 45° from the optical axis OA as shown in
In one disclosed embodiment, a plurality of LEDs are arranged on a support in a linear array, with the optical axes of the LEDs included in a first imaginary plane perpendicular to the support. An imaginary linear focal axis extends through the dies of the plurality of LEDs. Reflecting surfaces extend along either side of the array, forming a concave reflective trough. The reflective trough may be generally defined by a parabolic curve having a focus coincident with the linear focal axis and projected along said axis to form a linear parabolic structure on which reflecting surfaces can be arranged. An elongated lens is positioned above the LEDs and longitudinally bisected by the first imaginary plane. The elongated lens and trough are configured so that light may not be emitted from the optical assembly without passing through the elongated lens or being redirected by the trough reflector. The elongated lens is configured to redirect light emitted from the array of LEDs (and not incident upon the reflecting trough) from its emitted trajectory into imaginary planes parallel with the first plane. The reflective trough redirects wide angle light (light not passing through the elongated lens) from a range of emitted trajectories into a range of reflected trajectories closer to the first plane. The redirection performed by the elongated lens may be described as “partially collimated” or “collimated with respect to the first plane.” Such partially collimated light retains the component of its emitted trajectory within the imaginary planes into which it is redirected, whereas fully collimated light is parallel with a line such as the optical axis of an LED.
In the disclosed embodiments, medial reflecting surfaces are also positioned between adjacent pairs of LEDs, to redirect a portion of the wide angle light from each LED into imaginary planes perpendicular to the first imaginary plane containing the optical axes of the LEDs. This subset of wide angle light from each LED is partially collimated with respect to an imaginary plane perpendicular to the first plane and including the optical axis of the respective LED. Light reflected from the medial reflecting surfaces retains the component of its emitted trajectory within the imaginary planes into which it is redirected, however this light must be further redirected by the elongated lens or trough reflector before being emitted from the optical assembly. Thus, the subset of wide angle light incident upon the medial reflectors may be fully collimated with respect to the respective LED optical axis before exiting the optical assembly, depending upon the specific configuration of the elongated lens and trough reflector.
The shape of the medial reflecting surfaces is dictated by their function, e.g., redirecting this subset of wide angle light into trajectories having a smaller angular component with respect to imaginary planes perpendicular to both the first plane (containing the optical axes of the LEDs) and a second plane containing the light emitting dies of the LEDs. These planes intersect at the linear focal axis of the assembly. It will be noted that the die of each LED typically includes a base that supports the light emitting die above a plane defined by a PC board upon which the LEDs are mounted. The imaginary second plane discussed in this application includes the LED dies and an imaginary linear focal axis passing through the LED dies. The medial reflecting surfaces may take many forms, but preferably comprise a convex surface when viewed looking toward the LED support (PC board). A preferred surface configuration for the medial reflecting surface partially collimates the subset of wide angle light incident upon the medial reflecting surfaces into imaginary planes substantially perpendicular to both the first plane containing the LED optical axes and the second plane passing through the LED dies. In the disclosed embodiments, the medial reflecting surfaces are defined by a segment of a parabola having a focus centered on the light emitting die of a respective LED. This parabolic segment is then rotated about the imaginary linear focal axis of the array to form a three dimensional surface. The medial reflecting surfaces on either side of a respective LED are mirror images of each other and adjacent medial reflecting surfaces meet at a semicircular peak. Other surface configurations approximating the intended function of the disclosed medial reflecting surfaces will occur to those skilled in the art. A semi-conical surface is an example of such an alternative configuration.
In the absence of the medial reflecting surfaces, the subset of wide angle light redirected by the medial reflecting surfaces would continue on its emitted trajectory and be lost (absorbed or scattered) within the assembly or be partially collimated by the trough reflector and elongated lens (into imaginary planes parallel with the first plane containing the LED optical axes). In either case, the retained component of the emitted trajectory of this subset of wide angle light (within the imaginary planes) means it cannot contribute to a majority of desirable light emission patterns and is effectively wasted.
The reflecting trough of the disclosed embodiment is constructed from a plurality of reflecting surfaces, some of which are surfaces of rotation centered on the optical axis of an LED and others are linear surfaces defined by a curve projected along the length of the trough. Each surface is selected to re-direct light incident upon it into a range of trajectories that will contribute to a desired light emission pattern. The size and/or shape of each of the several reflecting surfaces may be adjusted to provide a desired light emission pattern.
It is known in the field of optics that reflecting surfaces may be formed as an internal reflecting surface or as polished or metalized external surfaces. Both types of surfaces are intended to be encompassed in the appended claims.
Referring to the drawings, wherein like numerals refer to like elements in the several Figures:
LED optical assemblies according to aspects of the present disclosure will now be described with reference to the figures, in which common reference numerals are used to designate similar components.
The disclosed optical assembly 10 includes a trough reflector 12 and a longitudinal lens 14. As shown in
The lens 14 includes a convex light input surface 24 facing the LEDs and a convex light emission surface 26 facing away from the LEDs 22. The convex curves defining the light input surface 24 and light emission surface 26 are projected along the length of the lens 14, resulting in a substantially constant sectional configuration. The geometry of the lens 14 is illustrated in
LEDs 22 as shown in
The reflector 12 in the disclosed embodiments includes parallel, mirror image reflecting surfaces extending along each side of the array of LEDs 22. The function of the reflector is to redirect light originating from the LEDs 22 into a range of angles having trajectories close to planes parallel with plane P1 which includes the optical axes OA of the LEDs 22. The trough reflector 12 is generally defined by a parabola 28 having a focus at the die of the LED 22. The shape of the reflector 12 is modified by superimposing surfaces defined by other curves onto the parabola 28 as will be discussed below. The disclosed trough reflector includes at least four distinct reflecting surfaces, each handling different portions of the light from the LEDs 22 and producing a portion of the resulting light emission pattern. Medial reflecting surfaces 30 are positioned to either side of each LED 22 and centered on the linear focal axis AL. These surfaces are defined by portions of parabola 28 rotated about the linear focal axis AL. The resulting surfaces of rotation redirect wide angle light from the LEDs 22 into planes such as P3 perpendicular to both the first plane P1 (containing the optical axes AO of the LEDs 22) and the second plane P2 (containing the light emitting dies of the LEDs 22). Other non-parabolic surfaces, such as conical surfaces may be used for the medial reflecting surfaces 30 as will occur to those skilled in the art. Some of the light redirected by the medial reflecting surfaces 30 will subsequently pass through the lens 14, resulting in fully collimated light parallel with the optical axis AO of the LED 22. This fully collimated light reinforces the straight ahead or on axis peak light output from the optical assembly 10. Light redirected by the medial reflecting surfaces 30 and not passing through the lens 14 will be incident upon the reflector 14.
The trough reflector 12 has two mirror image parallel reflecting surfaces. Each of these surfaces includes three distinct reflecting portions. Rotated portions 32 extend from the bottom to the top of the trough in a direction parallel with plane P3 as shown in
Each of the linear reflecting surface portions 34, 36 and 38 are defined by a segment of an elipse projected along the linear focal axis AL of the optical arrangement 10.
As shown in
The medial reflectors are configured to redirect this light into trajectories that will contribute to the overall light emission pattern. Generally speaking, such redirected trajectories are those closer to the optical axis OA of the respective LED 22 and/or further from the linear focal axis AL of the assembly. One disclosed configuration for the medial reflecting surface is defined by a parabolic curve having a focus at the area of LED light emission and rotated about the linear focal axis AL. Light incident upon the medial reflecting surfaces 30 is redirected into planes P3 perpendicular to both plane P2 and the plane P1 containing the optical axes OA of the LEDs 22. Light redirected by the medial reflecting surfaces 30 retains the component of its emitted trajectory within the planes P3 until passing through the longitudinal lens 14 or being reflected by the trough reflector 12. Light that is first redirected by the medial reflecting surfaces and then by the longitudinal lens 14 is fully collimated (parallel) with respect to the optical axis of the respective LED 22. Thus light incident upon the medial reflecting surfaces 30 is incorporated into a desirable light emission pattern.
Those skilled in the art will recognize that a reflecting surface may be an external, polished or metalized surface or may be an internal surface of an optical solid, or so-called internal reflecting surface.
While exemplary embodiments have been set forth for purposes of illustration, the foregoing description is by way of illustration and not limitation. Accordingly, various modifications, adaptations and further alternatives may occur to one of skill in the art without the exercise of invention.
