JP6749084B2 - LED lighting device - Google Patents

Description

The present invention relates to an LED lighting device used for an endoscope or the like.

The illumination light of the endoscope is guided from the light source to the tip by an optical fiber and is irradiated. A xenon lamp of about 100 to 300 W is often used as a light source, and an input of 200 to 300 lm/mm ² or more is required for an optical fiber having a diameter of 1 to 3 mm. In recent years, efforts have been made to adopt an LED lighting device as a light source in order to prolong the life and improve the efficiency. (See Patent Documents 1, 2, and 3)

JP, 2009-198736, A JP, 2007-148418, A Special table 2013-515346 gazette

Patent Document 1 relates to an illuminating device and an endoscope device that image the output light of an LED on an end surface of an optical fiber by a lens optical system, and optimizes an incident NA (Numerical Aperture) and an outgoing NA of the optical system. Is described. In this method, when the entire optical flux of the LED is focused on the end face of the optical fiber with the same NA as the optical fiber NA using the ideal optical system, according to the etendue conservation law,
LED diameter x LEDNA = optical fiber diameter x optical fiber NA
The relationship is established.

In a chip LED with a Lambertian distribution of light emission angles, LEDNA=1
LED diameter = optical fiber diameter x optical fiber NA
Becomes Therefore, for example, the entire luminous flux of the LED having a diameter of 1 mm can be incident on the optical fiber having a diameter of 1.67 mm and NA of 0.6.

However, the invention described in Patent Document 1 has a problem that when an LED having a brightness of 100 Mcd/m ² is used, the optical fiber input is 113 lm/mm ² , which is smaller than that of a xenon lamp.

Further, in FIG. 7 of Patent Document 2, an LED and an optical fiber are butted against each other. If the LED and the optical fiber have the same shape, the entire light flux is once incident on the end face of the optical fiber. Rays leak out of the optical fiber and are not guided to the emission end. The incident efficiency of this method is as follows:
Optical fiber input/LED output=optical fiber NA ² =0.6 ² =0.36
Becomes

Therefore, the invention described in Patent Document 2 has a problem that when an LED with a brightness of 100 Mcd/m ² is used, the optical fiber input is 113 lm/mm ² , which is less than that of a xenon lamp.

Further, FIG. 2 of Patent Document 3 is effective as a method of returning a part of the LED light to the LED by a hemispherical mirror to increase the brightness of the LED, but there is a problem in the LED shape, arrangement, condenser lens, etc. However, there was a problem of reducing efficiency.

The present invention is an LED lighting device including an LED and a hemispherical mirror, wherein the LED has a light emitting portion having a planar and point-symmetrical shape, a light emitting angle distribution is a Lambertian distribution, and a light emitting surface is a diffusion surface. , The hemispherical mirror has a reflective surface on the inner surface thereof, has an opening in the center, the reflective surface is arranged toward the LED, the normal line of the LED and the optical axis of the hemispherical mirror match, The distance between the LED and the hemispherical mirror is less than or equal to the radius of curvature of the hemispherical mirror, the size of the opening of the hemispherical mirror is approximately equal to the irradiation size, the LED size is dLED, and the distance between the LED and the hemispherical mirror is When t and the irradiation NA are NAobject, sin(tan ⁻¹ dLED/2t)≈NAobject is established.

Further, the present invention is an LED lighting device including an LED and a plano-convex lens mirror, wherein the LED has a light emitting portion having a planar and point-symmetrical shape, a light emitting angle distribution is a Lambertian distribution, and a light emitting surface is diffused. In the plano-convex lens mirror, the convex inner surface periphery forms a reflection surface, and the opening of the reflection surface is formed at the center, and the flat surface sides of the LED and the plano-convex lens mirror face each other and are spaced in parallel. The normal line of the LED is aligned with the optical axis of the plano-convex lens mirror, and the distance between the LED and the spherical surface of the plano-convex lens mirror is less than or equal to the radius of curvature of the plano-convex lens mirror. When the size of the opening is almost equal to the irradiation size, the LED size is dLED, the distance between the LED and the plano-convex lens mirror is t, the refractive index of the plano-convex lens mirror is n, and the irradiation NA is NAobject, nsin(tan ^-1 dLED/2t)≒NAobject

Furthermore, the present invention is characterized in that an optical fiber is arranged at the position of the mirror opening, and the irradiation NA is substantially equal to the optical fiber NA.

According to the present invention, it is possible to obtain various excellent effects such as realizing an LED lighting device having a large input without changing the LED output.

FIG. 3 is a ray tracing diagram in the LED lighting device according to the first embodiment of the present invention. It is a ray tracing figure in the conventional LED illuminating device for optical fibers. It is a ray tracing figure in the LED illuminating device which concerns on the 2nd Embodiment of this invention. It is a calculated value of an optical fiber input of NA 0.6 in the LED lighting device according to the first embodiment of the present invention. It is a calculated value of an optical fiber input of NA 0.2 in the LED lighting device according to the first embodiment of the present invention. FIG. 3 is a Monte Carlo simulation ray tracing diagram in the LED lighting device according to the first embodiment of the present invention. It is an illuminance distribution chart of the irradiation surface in the LED lighting device according to the first embodiment of the present invention. FIG. 3 is a far-field illuminance distribution diagram in the LED lighting device according to the first embodiment of the present invention. It is a calculated value of an optical fiber input of NA 0.6 in the LED lighting device according to the second embodiment of the present invention. It is a calculated value of an optical fiber input of NA 0.2 in the LED lighting device according to the second embodiment of the present invention. It is a Monte Carlo simulation ray tracing figure in the LED lighting apparatus which concerns on the 2nd Embodiment of this invention. It is an illuminance distribution chart of the irradiation surface in the LED lighting device according to the second embodiment of the present invention. It is a far-field illuminance distribution chart in the LED lighting device which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the LED illuminating device which concerns on this invention. It is a ray tracing figure in the LED lighting apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows the Monte Carlo simulation result of the illuminance distribution in the LED lighting apparatus which concerns on the 3rd Embodiment of this invention.

Hereinafter, an LED lighting device according to an embodiment of the present invention will be described in detail with reference to the drawings.

First, referring to FIGS. 1 and 2, a ray tracing diagram in the LED lighting device according to the first embodiment of the present invention and a ray tracing diagram in the conventional LED lighting device for optical fiber will be described.

FIG. 2 shows a ray tracing diagram of a conventional LED light source for a butt-coupling optical fiber.
The diameter of LED1: dLED is 4 mm, the diameter of optical fiber 8: dfiber is 3 mm, and the optical fiber NA: NAfiber is 0.6. The distance between LED1 and optical fiber 8 is sufficiently small, and the normal line of LED1 and optical fiber 8 are The optical axes are arranged so as to coincide with each other.

The light ray 62 emitted from the LED 1 outside the diameter of the optical fiber does not enter the end face 2 of the optical fiber 1 and is not guided by the optical fiber. The light beam emitted from the LED 1 inside the optical fiber diameter is incident on the end face of the optical fiber 8, but the light beam 6 incident with a larger NA than the optical fiber NA is emitted outside from the side surface of the optical fiber 8. The light is not guided to the exit end 9 of the light source 8. The guided light beam 5 is a light beam that is emitted from the inner side of the optical fiber diameter and that is incident on the optical fiber 8 with an NA equal to or less than the NA of the optical fiber 8.

Therefore, the efficiency of this optical system is as follows: light quantity guided by the optical fiber 8/output light quantity of LED1=(dfiber/dLED)^2xNAfiber^2
=(3/4)^2x0.6^2=0.203
Becomes

The present invention optimizes the distance between the LED 1 and the optical fiber 8 to make the incident NA and the NA of the optical fiber 8 coincident with each other, and returns light with a large NA that cannot be guided by the optical fiber 8 to the LED 1 by the mirror 3 to diffuse the LED 1. The light input to the optical fiber 8 is increased by converting the light so that the light can be guided by the optical fiber 8.

FIG. 1 shows a ray tracing diagram of an LED lighting device 4 according to a first embodiment of the present invention. A light source device including a light emitting portion having a planar and point-symmetrical shape, a light emitting angle distribution having a Lambertian distribution, a light emitting surface being a diffusing surface, and a hemispherical mirror 3 having an inner surface forming a reflecting surface 3a and an opening 3b in the center. Then, the reflection surface 3a is arranged toward the LED 1, the normal line of the LED 1 and the optical axis of the hemispherical mirror 3 coincide with each other, and the distance between the LED 1 and the hemispherical mirror 3 is less than or equal to the radius of curvature of the hemispherical mirror 3, The optical fiber 8 is arranged in the opening 3b, and the diameter of the opening of the hemispherical mirror 3 is equal to the diameter of the optical fiber.

The light beam emitted from the LED 1 and passing through the opening 3b of the hemispherical mirror 3 is directly incident on the end face of the optical fiber 8. Of these light rays, the light guided by the optical fiber 8 must enter with an NA equal to or less than the NA of the optical fiber 8. In the case of a light beam traveling from the upper end of the LED to the center of the optical fiber in FIG. 1, the light is not guided unless the sine of the angle θ with the optical axis of the optical fiber 8 is equal to or smaller than the NA of the optical fiber 8.

That is, the following relationship holds.
sin θ = sin(tan ^-1 dLED/2t) ≤ NA fiber
Here, t is the distance between the LED 1 and the center of the hemispherical mirror 3.
Under this condition, the incident NA of the light ray 61 incident from the upper end of the LED 1 to the lower end of the optical fiber 8 is larger than that of the optical fiber NA and is not guided. On the contrary, the light ray 51 emitted from the upper end of the LED 1 and incident on the upper end of the optical fiber 8 has a sufficient margin for the guide limitation by the NA of the optical fiber 8. To obtain high incidence efficiency for all the light rays emitted from LED1,
sin(tan ^-1 dLED/2t)≒NA fiber
Is desirable.

The light ray 6 that cannot be guided by the optical fiber 8 forms the LED1 image on the LED1 in point symmetry by the reflecting surface 3a. In order for the LED1 and the LED1 image to match, the shape of the LED1 must be point-symmetrical. If the emission angle distribution of the LED 1 is a Lambertian distribution, all the light rays 6 emitted by the reflecting surface 3a except the opening 3b can be returned to the LED 1 side. If the surface of the LED 1 is a diffusion surface, the light rays returned to the LED 1 are diffused and emitted toward the opening 3b and the reflection surface 3a. The light beam directed to the opening 3b contributes to an increase in the input of the optical fiber 8. The light directed to the reflecting surface 3a is also emitted from the opening 3b while being repeatedly reflected and diffused between the LED 1 and the mirror 3.

FIG. 3 shows a ray tracing diagram of the LED lighting device 4 according to the second embodiment of the present invention. An LED 1 having a plane and point-symmetrical shape, a Lambertian distribution of emission angles, a light emitting surface that is a diffusing surface, and a plano-convex lens in which a reflective surface 7a is formed around the inner surface of the convex surface and an opening 7b of the reflective surface is formed in the center. In the light source device including the mirror 7, the flat sides of the LED 1 and the plano-convex lens mirror 7 face each other and are arranged in parallel with a space therebetween, and the normal line of the LED 1 and the optical axis of the plano-convex lens mirror 7 coincide with each other. The distance between the spherical surfaces is less than or equal to the radius of curvature of the plano-convex lens mirror 7, the optical fiber 8 is arranged in the mirror opening 7b, and the mirror opening diameter is equal to the optical fiber diameter.

The light beam emitted from the LED 1 and passing through the opening 7b of the plano-convex lens mirror 7 directly enters the end face of the optical fiber 8. Of these light rays, the light guided by the optical fiber 8 must enter with an NA equal to or less than the NA of the optical fiber 8. In the case of a light beam traveling from the upper end of the LED 1 to the center of the optical fiber 8 in FIG. 3, it is not guided unless the sine of the angle θ with the optical axis of the optical fiber 8 in the lens is equal to or smaller than the NA of the optical fiber 8.

That is, the following relationship holds.
nsin θ = nsin(tan-1dLED/2t) ≤ NA fiber
Here, n is the refractive index of the lens, and t is the distance between the LED 1 and the center of the reflecting surface. The distance between the LED and the optical fiber and the plano-convex lens mirror is sufficiently smaller than t.

Under this condition, the incident NA of the light ray 61 incident from the upper end of the LED 1 to the lower end of the optical fiber 8 is larger than that of the optical fiber NA and is not guided. On the contrary, the light ray 51 emitted from the upper end of the LED 1 and incident on the upper end of the optical fiber 8 has a sufficient margin for the guide limitation by the NA of the optical fiber 8. To obtain high incidence efficiency for all the light rays emitted from LED1,
nsin(tan ^-1 dLED/2t)≒NAfiber
Is desirable

The light ray 6 which cannot be guided by the optical fiber 8 forms the LED1 image point-symmetrically on the LED1 by the reflecting surface 7a. In order for the LED1 and the LED1 image to match, the LED1 shape must be point-symmetrical. If the light emission angle distribution of the LED 1 is a Lambertian distribution, most of the light rays 6 emitted from the reflection surface 7a except the opening 7b can be returned to the LED 1 side. If the LED1 surface is a diffusing surface, the light rays returned to the LED1 are diffused and emitted toward the opening 7b and the reflecting surface 7a. The light beam directed to the opening 7b contributes to an increase in the input of the optical fiber 8. The light heading for the reflecting surface 7a is also emitted from the opening 7b while being repeatedly reflected and diffused between the LED1 and the reflecting surface 7a.

FIG. 4 and FIG. 5 are mirror curvature radii of incidence efficiency (optical fiber incident light flux/LED output light flux) with respect to the optical fiber 8 of NA 0.6 and NA 0.2 in the LED lighting device according to the first embodiment of the present invention: It is a figure which shows the result of the Monte Carlo simulation which used r as a parameter. However, LED diameter: 4 mm, mirror aperture diameter=fiber diameter: 3 mm, and the reflectance of the mirror 3 and the LED 1 is 0.95.

For the optical fiber 8 having NA of 0.6, the efficiency peaks at the distance t between the centers of the LED 1 and the mirror 3 of 2.8 mm. For the optical fiber 8 with NA of 0.2, the longer t is, the better the efficiency is. When the incident NA is set to 0.6, the incident efficiency with respect to the NA of 0.6 is prioritized, but if the efficiency is the same, the efficiency with respect to the optical fiber 8 with the NA 0.2 having many components in the optical axis direction at the exit end is high. Higher is preferable. Therefore, r=3.5 mm and t=3 mm were selected. The distance between the center of the mirror 3 and the optical fiber 8 is 0 mm, and the distance between the Φ3 mm opening and the optical fiber 8 is 0.34 mm.

FIG. 6 is a Monte Carlo ray trace diagram of the LED light source device of the above design. It can be seen that many light rays travel back and forth between the LED 1 and the mirror 3, and only the light rays that have reached the opening are input to the optical fiber 8.

FIG. 7 is an illuminance distribution on the incident end surface of the optical fiber 8. Since there is a distance from the mirror 3, the illuminance distribution is somewhat wider. FIG. 8 shows the illuminance distribution at a position 100 mm away from the diaphragm, with the optical fiber 8 removed and a diaphragm of Φ3 mm placed at the end face position of the optical fiber 8. 4% of light rays having NA of 0.6 or more (x-axis coordinate of 75 mm or more and −75 mm or less) that cannot be incident on the optical fiber 8 are also included. The 10% NA (sine of the angle of 10% illuminance with respect to the central illuminance) is 0.62, and the incidence efficiency on the 0.6 optical fiber 8 is 0.35, which is 1.7 times that of the conventional matching method. When an LED with a brightness of 100 Mcd/m ² is used, the input to the optical fiber 8 is 190 lm/mm ² , and it approaches a xenon lamp.

In the present invention
sin(tan ^-1 dLED/2t) = sin (tan ^-1 4/(2x3)
=0.55≈0.6=NA fiber design value target≈0.62=10% NA calculated value holds.

FIG. 9 and FIG. 10 show the results of Monte Carlo simulation using the mirror curvature radius: r of the incident efficiency with respect to the optical fiber 8 of NA 0.6 and NA 0.2 as a parameter in the LED lighting device according to the second embodiment of the present invention. It is a figure. However, LED diameter: 4 mm, aperture diameter of mirror 7 = fiber diameter: 3 mm, LED1-plano-convex lens 7 spacing: 0.1 mm, plano-convex lens 7-optical fiber 8 spacing: 0.5 mm, plano-convex lens 7 refractive index : 1.516, the reflectance of the reflecting surface 7a and the LED 1 is 0.95.

FIG. 11 is a Monte Carlo ray tracing diagram of the LED light source device in which r=6 and t=4.7 mm are selected with respect to the design target NA0.6.

FIG. 12 is an illuminance distribution on the incident end surface of the optical fiber 8. FIG. 13 shows the illuminance distribution at a position where a Φ3 mm diaphragm is placed at the position of the end face of the optical fiber 8 and a position 100 mm away from the diaphragm. A light ray having NA of 0.6 or more that cannot be incident on the optical fiber 8 is also included by 3%. When the 10% NA is 0.6, the incidence efficiency on the optical fiber 8 of 0.6 is 0.4, which is twice as high as that of the conventional butt matching method. When an LED with a brightness of 100 Mcd/m ² is used, the optical fiber input becomes 226 lm/mm ² , which is closer to the xenon lamp.

In the present invention, nsin(tan ^-1 dLED/2t)=1.516xsin (tan ^-1 4/(2x4.7)
=0.59≈0.6=NA fiber design value target≈0.6=10% NA calculated value holds.

FIG. 14 shows an optical sectional view of the white LED according to the present invention. The LED 1 is composed of a mirror layer 12, a semiconductor 11 (a PN junction 11b in the center and a diffusion layer 11d on the front surface), and a fluorescent layer 13 from the back side on the left side of the drawing. Blue light rays 21a and 21b are generated at the PN junction. 21a is diffused by the diffusion layer and divided into a light ray 22a directed to the front surface and a light ray 22b directed to the back surface. The light ray 22a is divided into yellow light rays 23a and 23b which are fluorescently diffused in the fluorescent layer and blue light rays 24a and 24b which are diffused. The light rays 23a and 24a are output from the LED as white light. The rays of light 21b and 22b directed toward the back surface are reflected by the mirror layer to become rays of light 25 and 26, which are incident on the diffusion layer, and behave similarly to the ray of light 21a. The light rays 23b and 24b enter the diffusion layer and behave like the light ray 21a.

The light ray 31 incident on the fluorescent layer from the outside is divided into fluorescent diffused light rays 32a and 32b and diffused light rays 33a and 33b. The light rays 32a and 33a are output to the outside of the LED 1, the light rays 32b and 33b enter the diffusion layer, and behave similarly to the light ray 21a.

If the thickness of each layer of the LED 1 of FIG. 14 is sufficiently thin with respect to the diameter of the LED 1, when the LED 1 is optically macroscopically viewed, it is a surface light emitter that emits light in a Lambertian distribution and is a diffuse reflection surface. It is a fluorescent diffuse reflection surface.

When the LED using the blue LED and the yellow phosphor is used in the present invention, the color temperature of the output light of the present invention is lower than that of the LED alone. This occurs because blue light, which is repeatedly reflected and diffused between the mirror and the LED, is absorbed by the fluorescent substance and emits yellow fluorescence, so that blue is relatively reduced and yellow is increased. To obtain the same color temperature, it is necessary to reduce the amount of fluorescent material.

FIG. 15 shows a third embodiment of the present invention. It is an example in which the LED light source device 4 according to the present invention is applied to the light source of the schlieren method device 40. The mirror opening serves as a pinhole for the schlieren device light source. 41 is a convex lens, 42 is a subject, 43 is a knife edge, and 44 is a screen. The LED light source device has an LED diameter of 4 mm, a plano-convex lens mirror has a radius of curvature of 10 mm, a thickness of 9.2 mm, a mirror aperture diameter of 1 mm, and an LED-plano-convex lens mirror interval of 0.2 mm.

FIG. 16 is a Monte Carlo simulation result of the illuminance distribution at a position 100 mm away from the mirror, and 10% NA is 0.339. In the present invention, nsin(tan ⁻¹ dLED/2t)=1.516×sin (tan ⁻¹ 4/(2×9.4)
=0.315≈0.339=10% NA calculated value holds. When the reflectivity of the LED and the mirror is 0.95, the brightness of the mirror opening is 6 times the brightness of the LED, and even when the reflectivity is 0.9, the brightness is 4 times.

1 LED
3 hemispherical mirror 3a reflecting surface 3b opening 7 plano-convex lens mirror 7a reflecting surface 7b opening 8 optical fiber

Claims (3)

An LED lighting device comprising an LED and a hemispherical mirror, comprising:
The light emitting portion of the LED has a planar and point-symmetrical shape, the light emitting angle distribution is a Lambertian distribution, and the light emitting surface is a diffusion surface,
The inner surface of the hemispherical mirror forms a reflecting surface, and an opening is formed at the center of the hemispherical mirror. The reflecting surface is arranged toward the LED, and light emitted from the LED and not reaching the opening is transmitted to the LED. Direct return,
The normal line of the LED and the optical axis of the hemispherical mirror match,
The distance between the LED and the hemispherical mirror is less than or equal to the radius of curvature of the hemispherical mirror,
The size of the opening of the hemispherical mirror is equal to the irradiation range irradiated from the opening,
When the LED size is dLED, the distance between the LED and the hemispherical mirror is t, and the NA of the light emitted from the opening is NAobject,
sin(tan ⁻¹ dLED/2t)≦NA object
The LED lighting device is characterized in that An LED lighting device comprising an LED and a plano-convex lens mirror,
The light emitting portion of the LED has a planar and point-symmetrical shape, the light emitting angle distribution is a Lambertian distribution, and the light emitting surface is a diffusion surface,
In the plano-convex lens mirror, the periphery of the inner surface of the convex surface forms a reflection surface, and the opening of the reflection surface is formed at the center, and the flat surface sides of the LED and the plano-convex lens mirror face each other and are arranged in parallel with each other, and Light emitted from the LED and not reaching the opening is returned directly to the LED,
The normal line of the LED and the optical axis of the plano-convex lens mirror match,
The distance between the LED and the spherical surface of the plano-convex lens mirror is less than or equal to the radius of curvature of the plano-convex lens mirror,
The size of the opening of the plano-convex lens mirror is equal to the irradiation range irradiated from the opening,
When the LED size is dLED, the distance between the LED and the reflecting surface of the plano-convex lens mirror is t, the refractive index of the plano-convex lens mirror is n, and the NA of the light emitted from the opening is NAobject,
nsin(tan ⁻¹ dLED/2t)≦NAobject
The LED lighting device is characterized in that The LED lighting device according to claim 1 or 2, wherein an optical fiber is arranged at the position of the mirror opening, and the NA of light emitted from the opening is equal to or less than the optical fiber.

Images