JP2007235079A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device which condenses emissive light from an LED element 1 at high efficiency. <P>SOLUTION: A lighting of high condensing efficiency is materialized: by allotting a surface light source comprising an LED element 1 in a rear part opening 4 of a reflector 3; and by emitting light from a front part opening 5. The reflector is a revolving surface reflector approximated to the shape of a basic form, wherein the ridge line is a part of parabola of the shape of the basic form or a link of cones approximated to the shape of the basic form. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting device for appropriately deflecting, controlling, and condensing light emitted from a light emitting diode (hereinafter, LED).

When the LED is used for illumination, it is necessary to deflect, control, and collect the emitted light of the LED using a lens or a reflecting mirror. The light distribution (luminance distribution) of the LED element can be approximated to a Lambertian type as shown in FIG. In contrast to this, although the light distribution required by a normal illumination application is 120 °, a wide-angle light distribution with a beam angle of 30 ° as shown in FIG. Alternatively, it is much narrower like a narrow-angle light distribution with a beam angle of 10 ° as shown in FIG.

As the LED light emitting device, the most common one is an optical system in which a convex lens 12 is arranged in front of the light emitting surface of the LED element 1 as shown in FIG. The light is refracted and deflected by a convex lens. (For example, refer to Patent Document 1.) The beam angle widens when the LED is placed forward, and narrows when lowered backward.
JP 2001-36148 A

On the other hand, as shown in FIG. (For example, refer to Patent Document 2.) In this case, the LED element 1 is installed in the vicinity of the focal point of the concave mirror 13 so as to face the concave mirror 13.
JP-A-6-260684

However, the conventional LED light-emitting device composed of this convex lens condensing system has two problems of low condensing efficiency and inappropriate light distribution shape.
In this convex lens condensing system, as can be seen from FIG. 3, only the radiated light from the LED element 1 to the angle range where the lens is expected is directed to the irradiation surface. In the case of this combination, the light collection efficiency is as low as 60% for a wide-angle light distribution with a beam angle of 30 ° and 20% for a narrow-angle light distribution with a beam angle of 10 °.
In addition, due to the nature of the lens condensing system, the luminous intensity in the center direction of the light distribution becomes too high, and there is a drawback that the illuminance distribution non-uniformity is too bright at the center of the irradiated surface.

On the other hand, since the conventional condensing system by the concave mirror reflects substantially the entire angular range of the LED radiation light, the condensing efficiency is high. However, the LED element itself has a structure in which the reflected light is blocked, and there is a drawback that it is difficult to use an LED having a very large area or to attach a heat radiating plate having a large heat radiating area.

A typical example of an LED light emitting device according to the present invention is shown in FIG.
It is a light emitting device comprising a rotating surface reflecting mirror 3 having an opening 4 and an opening 5 in the front and rear, and a surface light source composed of a large number of LED elements 1 in close contact with the heat radiating plate 2. . Radiant light emitted forward (right side in FIG. 1) from the LED element installed on the rear opening 4 side is reflected by the inner surface of the reflecting mirror and then emitted from the front opening 5 or directly from the front opening 5. The The reflecting mirror 3 is a rotating surface reflecting mirror formed by rotating a curved arc or a polygonal arc around an optical axis 6 (a line connecting the center of the irradiation surface and the light emitting device). The line arc to be rotated is hereinafter referred to as the ridgeline of the rotating surface, but the reflector ridgeline of the LED light emitting device according to the present invention is a curved arc that approximates or is close to the ridgeline of the following reflector basic shape. Or it is a broken line arc.
The rotation of the curved arc around the optical axis gives a rotating curved surface, and the rotation of the polygonal arc gives a chain of cones.

That is, the basic shape of the reflecting mirror 3 is as follows with reference to the sectional view of only the reflecting mirror of FIG. This basic shape is formed by rotating a part of the parabola around the optical axis 6 as a ridge line.
First, the size of the circular rear opening 4 is set so as to meet the required LED light emitting area of light output.
Next, the size of the circular front opening 5 is larger than that of the rear opening 4, and straight lines 9 a and 9 b connecting both ends A and B of the rear opening 4 and opposite ends D and E of the front opening 5 are provided. The formed angle θ (referred to as the opening angle of the reflecting mirror) is set so as to substantially match the angle at which the desired irradiation range is expected from the light emitting device. The position of the front opening is set in the vicinity of the position where the parabola 10 generated by the following method and the straight line 9a indicating the opening angle intersect. Here, the parabola 10 is focused on one end A of the rear opening with θi being a half of the desired beam angle (half-value angle width of the desired luminous intensity distribution), passes through this focal point, and is in a plane including the optical axis 6. Thus, it is assumed that a straight line 7 inclined by an angle θi with respect to the optical axis 6 is a central axis and passes through one end B on the opposite side to the focal position of the rear opening.

In the LED light emitting device according to the present invention, it is desirable that the entire area of the rear opening 4 emits light with a substantially uniform luminance distribution, and it is necessary that the total surface area of the LED elements is at least 30% or more of the rear opening area. Here, the LED element surface area is defined as “light emitting part area + surface area of the substrate exposed surrounding the light emitting part” of the LED element. This is because a light source of a condensing system can be regarded as shining uniformly even if there are some gaps between the LED elements.
In the case where the light source is formed by a single LED element or an LED with a phosphor, it is desirable to match the shape of the rear opening with a circular approximation such as a circle or a hexagon. When a plurality of LED elements are installed, it is desirable to spread the LED elements over the entire rear opening in a grid pattern or the like. Further, when a white light source is formed by combining red, green, and blue LED elements, it is necessary to obtain a constant and uniform luminance distribution for each color.
Further, the gap between the spread LED elements is preferably smaller when the LED light emitting device is used for illumination, and larger when it is used for display and display. In the latter case, it is necessary to process the surface of the heat sink in the gap between the LED elements to be black and suppress reflection of light as much as possible.

In FIG. 5, the reflecting mirror when θ = 2θi is referred to as a CPC (Compound Parabolic Concentrator). (For example, refer nonpatent literature 1) FIG. 6: is the tracking result of the light ray emitted in each direction from the center C and the edge part A of the rear opening 4 which is a light ray incident hole in this CPC11. From this figure, it can be seen that most of the light rays are emitted inside the opening angle of the reflecting mirror (the angle formed by the straight lines 8a and 8b). As a result of ray tracing for rays emitted from various positions of the rear opening surface 4 or various rays (so-called skew ray) intersecting with the plane including the optical axis, most of the rays are within the cone where the opening angle θ is expected. It was found that it was emitted in the direction.
FIG. 7 shows the luminous intensity distribution and the illuminance distribution in a remote area (at a position sufficiently away from the light emitting device) by the CPC shown in FIG. 6 in which a surface light source having a uniform luminance distribution is arranged on the entire rear opening. is there. Also from this figure, it can be seen that most of the emitted light beam is radiated inside the opening angle of the reflecting mirror, that is, the desired irradiation angle.
In the case of a condensing system using a reflecting mirror, a reduction in condensing efficiency due to light absorption on the reflecting surface is unavoidable, but in the condensing system of FIG. 7, even if the reflectance of the reflecting surface is 90%, the condensing efficiency is 85. %, The light collection efficiency is significantly higher than the conventional example of the convex lens condensing system.
W. T.A. Welford, R.A. Winston “High Collection Nonimaging Optics” p53 (Academic Press, Inc. 1989)

As shown in FIG. 7 indicated by CPC, the illuminance distribution where the irradiation surface boundary stands out is not generally welcomed in the lighting application field. In many cases, as shown in FIG. 8, an illuminance distribution in which the illuminance at the boundary of the irradiation surface fades out toward the outside, that is, a light distribution whose beam angle is narrower than the expected angle of the irradiation surface is desired.
FIG. 8 shows the luminous intensity distribution and the illuminance distribution by the cone chain reflecting mirror shown in FIG. 1 in which a surface light source having a constant and uniform luminance distribution is arranged on the entire rear opening. Most of the emitted light beam is emitted inside the opening angle of the reflecting mirror, that is, the desired irradiation angle, and the half-value angle width of the luminous intensity distribution is substantially equal to the set beam angle. The light collection efficiency (the ratio of the incident range incident light beam to the light source emitted light beam) was 87% when the reflector reflectance was 90%.
In a conventional condensing system using a convex lens, the illuminance distribution has a mountain shape, and a relatively uniform illuminance distribution within the beam angle range as shown in FIG. 8 cannot be realized.

In the case of the configuration of the present invention, as described above, in principle, the surface light source arranged in the rear opening of the reflecting mirror shines with a substantially uniform luminance distribution over the entire opening. However, if the uniform light emitting area of the surface light source (when LED elements are arranged, the total occupied area of the LED elements, that is, the total surface area of the LED elements) is 30% or more of the rear opening area of the reflector, it is smooth. A luminous intensity distribution or illuminance distribution can be obtained.
For example, FIG. 9 shows the illuminance distribution when the occupancy ratio of the uniform luminance light emitting area in the rear opening area of the reflector is 25% in the same optical system as in FIG. Illumination unevenness of about 20% is shown in both cases, in which only the circular part of the case emits light and only the ring part around the periphery of the rear opening on the right side of FIG. This 20% illuminance unevenness is judged to be a practically allowable limit. Therefore, as a light source constituting the present invention, a single LED element having a surface area of 30% or more of the rear opening area of the reflector, Alternatively, a surface light source composed of a plurality of LED elements laid down is adopted.

A non-surface light source such as a general halogen lamp or a fluorescent lamp can be sandwiched between a reflection plate and a diffuse transmission plate to form a surface light source having a uniform luminance distribution. As a whole, the optical system as a whole has a very low light collection efficiency. This is why a highly efficient bare LED element or LED with phosphor is recommended as the light source constituting the present invention.

In application to the field of LED lighting, it is desirable to use a light source having a large luminous flux and a small size. For this purpose, the LED light emitting efficiency is maximized per unit light emitting area while maintaining the LED operating temperature at which the LED luminous efficiency is maximized. It is necessary to use input power. In the case of an LED element for illumination, the LED element is in close contact with the rear surface of the light emitting surface, and a heat sink attached is provided with a surface area as large as possible to inject a large amount of power.
In the configuration of the present invention, it is the same as the conventional example of the convex lens described above. Compared to the conventional example of the reflector, there is a margin for mounting the heat sink on the back of the LED, but the reflector is made of metal and is shown in FIG. As described above, a large-area heat radiating plate can be obtained by closely bonding the reflecting mirror to the flat heat radiating plate behind the LED. In this way, a light source with much higher power and larger luminous flux than the conventional example can be made.

The light-emitting device having the configuration of the present invention is useful as a display element applied to a signal lamp, a large outdoor display, and the like in addition to the illumination application. This is because the luminance distribution is uniform over the entire front exit surface. In addition, when this apparatus is used as a display element, the beam angle is the viewing angle. However, if the reflecting mirror according to claim 1 is used, the luminance is substantially constant when viewed from any angle within the viewing angle. There is also an advantage. This can be estimated from the fact that the light intensity is substantially constant within the range of the beam angle in FIG.
But there are drawbacks. Since the reflectance of the LED element itself is quite high, it is easy to reflect external light. For this reason, the contrast of the display element is lowered.
In a surface light source composed of a plurality of LED elements arranged on a heat sink having the same shape as that of the rear opening, arranged at the rear opening of the reflector, the filling factor (the sum of the light emitting areas of the LED elements / the area of the rear opening) If the LED elements are arranged evenly with a gap so as to be between 30% and 70%, and the heat sink surface in the gap between the LED elements is processed into black, the reflectance of the surface light source decreases, A reduction in contrast can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The LED light source 1 in FIG. 1 has a large number of LED elements 1 for red light emission (r), green light emission (g), and blue light emission (b) on the entire surface of the circular heat sink 2 as shown in an enlarged view in FIG. , A white light source arranged. Since a large number of LED elements of each color are uniformly distributed over the entire surface of the circular heat sink 1, a uniform and uniform luminance distribution is obtained for each color.

The reflecting surface shape design method and design steps of the reflecting mirror are as follows with reference to FIGS.
1. A rear opening diameter d1 that is the same as the diameter of the circular surface light source is set.
2. A desired beam angle is set to 2θi, and a straight line 7 passing through one end A of the rear opening and inclined by an angle θi from the optical axis 6 is set as a central axis, and one end B facing the A point of the rear opening is focused on this A point. Draw a parabola 10 through. The focal length f of the parabola 10 can be calculated by the following equation.
f = d1 · (1 + sin θi)
3. A rotating surface formed by rotating the parabola 10 around the optical axis 6 is set as a basic shape of the reflecting mirror.
4). A straight line 9a that passes through the point A and is inclined by θ / 2 with respect to the optical axis has a front opening at a position in the optical axis direction at a point D that intersects the parabola 10 with an apex angle that anticipates a desired irradiation range as θ. Set, and double the vertical distance of the point D from the optical axis is the diameter d2 of the front opening.
5). With respect to the reflecting mirror 11 of FIG. 5 generated in the above steps, the light intensity distribution when a circular surface light source having a constant uniform luminance and a diameter d1 is arranged in the rear opening 4 is calculated, and this coincides with the desired light intensity distribution. Then, the design is finished here.
6). If the desired luminous intensity distribution cannot be obtained in step 5, the reflecting mirror 11 of FIG. 5 is appropriately divided in the optical axis direction (at an interval that is inversely proportional to the gradient of the ridge line, about 10 divisions), as shown in FIG. A reflecting mirror composed of a chain of cones, which is similar to the reflecting mirror 11, is generated. The ridge line of the cone chain forms a broken line, and the bending point of the broken line is on the ridge line of the reflecting mirror 11 in FIG.
7). The luminous intensity distribution is calculated for the reflector 3 made of a chain of cones obtained in Step 6, and if this does not match the desired luminous intensity distribution, the bending point of the broken line is moved slightly, that is, the diameter of the cone is finely adjusted. Then, the light intensity distribution is calculated again.
8). Step 7 is repeated, and when the desired light intensity distribution is achieved, the design is finished here.

FIG. 1 shows an embodiment of a light-emitting device designed for high-efficiency illumination with a wide-angle light distribution with a beam angle of 30 ° and a luminous intensity distribution that fades out to an opening angle of 40 °.
In the planar light source, 60 LED elements 1 are laid on a heat radiating plate having a diameter of 4 mm for each of red light emission (r), green light emission (g), and blue light emission (b). The substrate of each LED element is 0.25 mm □, that is, the total LED element surface area is 11.25 mm ² , and the ratio (occupancy ratio) of this area to the rear opening area of the reflector is 90%. In addition, the light emission part of each LED element is 0.2 mm □, and the total light emission area is 7.2 mm ² .
The circular heat generating plate 2 is made of a heat conductive material such as aluminum, and each LED element is attached in close contact with the heat radiating plate, so that the LED element is cooled by the heat radiating plate 1. Thus, the electrical input of the entire LED element can be 7 W to 15 W.
Since the luminous efficiency of the LED is 80 lm / W, the total luminous flux of the surface light source of this embodiment is 560 lm to 1200 lm.

The reflecting mirror 3 in FIG. 1 can be made, for example, by pressing an aluminum plate. If the inner surface is polished, a reflectance of about 90% can be realized.
In this example, since the luminous intensity distribution that fades out sufficiently smoothly was not obtained in the step 5 described above, the process proceeds to step 8. Finally, the positions of the five bending points on the rear opening side were moved 0.1 to 0.3 mm outward.
The final design result is the cone-chain reflecting mirror 3 of FIG. 1, d1 = 4 mm, d2 = 14.45 mm, and L = 21.06 mm.

FIG. 8 shows the luminous intensity distribution and the illuminance distribution shown by the light emitting device of this example. When the reflectance of the reflector is 90%, the light collection efficiency is 87%, which is considerably higher than that of the conventional one. The peak luminous intensity is calculated to be 2150 cd to 4600 cd, assuming that the electric input is 7 W to 15 W.

In the embodiment of FIG. 1, the aluminum reflecting mirror 3 is integrated with the radiator plate 2. Thus, if the heat radiation area is increased, a large electric input can be obtained, and the above-described upper limit 15 W of the electric input is a result of this treatment.

Sectional drawing which shows embodiment of the LED light-emitting device by this invention. The graph which shows the light distribution of a LED element, and the target light distribution of a light-emitting device. Sectional drawing and optical path figure which show the prior art example of LED light-emitting device. Sectional drawing and optical path figure which show the prior art example of LED light-emitting device. The figure explaining the basic shape of the reflective mirror in connection with this invention. Sectional drawing and optical path diagram of CPC. The graph which shows the light intensity distribution and illumination intensity distribution by CPC. The graph which shows the luminous intensity distribution by the LED light-emitting device of this invention, and illumination intensity distribution. The graph which shows the relationship between the light source shape and illuminance distribution in the LED light-emitting device of this invention. The figure which shows one Example of the LED surface light source used for the LED light-emitting device of this invention.

Explanation of symbols

1, 1r, 1g, 1b LED element 2 Radiator 3 Reflector 4 Reflector rear aperture 5 Reflector front aperture 6 Optical axis 7 Parabolic center axis 8a, 8b Beam angle straight lines 9a, 9b Open angle Straight line 10 shown Parabola 11 Basic shape of rotating surface reflector 12 Convex lens 13 Concave reflector

Claims (1)

A surface light source composed of a single light-emitting diode element, or a surface light source formed by arranging a plurality of light-emitting diode elements; and a rotating surface-shaped reflecting mirror having openings on the front and rear sides; (1) (2) the total surface area of the light emitting diode elements is the rear opening of the reflecting mirror, and the light emitting portion of the surface light source is disposed inside the rear opening. (3) the diameter of the front opening of the reflector is larger than the diameter of the rear opening, and (4) the ridgeline of the reflector is on the periphery of the front opening. A light-emitting device characterized by being a curved arc or a polygonal arc in the vicinity of a parabola focused on a position opposite to the ridgeline.

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