Light guide, lighting device, image sensor and reading device

Abstract

This invention relates to a light guide, an illumination device, an image sensor, and a reading device. The light guide is columnar and includes a light-injecting surface disposed on a first end face, a light-emitting surface disposed on a side face along the long side direction of the light guide, and a first interface, a second interface, and a third interface disposed between the light-injecting surface and the light-emitting surface.

Description

Technical Field

[0001] This invention relates to a light guide, an illumination device, an image sensor, and a reading device. Prior Technology

[0002] Previously, lighting devices that use light guides (also known as light guides) to provide linear illumination to objects were well known. The function of such lighting devices is to allow light to enter from at least one end of a long light guide in one direction and propagate along the long side of the light guide, while simultaneously allowing the light to shine in a straight line along the long side from at least one light-emitting surface.

[0003] If an illumination device is constructed using a long light guide with a light source positioned at at least one end, the light emitted from the light source at the end will enter through the end face of the light guide and propagate along its long side. A portion of the light propagated by the light guide will be reflected and scattered along at least one light reflecting surface along its long side, and then exit from the light emitting surface opposite the light reflecting surface. However, a portion of the light entering the light guide from the end face with the light source will not be reflected or scattered at the light reflecting surface, but will directly reach the light emitting surface and exit. This phenomenon occasionally occurs near the light source. As a result, the illumination light from the illumination device may have a high intensity light distribution near the light source.

[0004] In order to ensure that the lighting device has an average light distribution, some measures are taken, such as optimizing the reflection and diffusion pattern of the light guide surface.

[0005] According to the description in reference 1, small apertures are formed at positions such as the end face where the light from the light source enters, the light emitting surface (light emitting part) of the light guide, and the light reflecting surface (light reflecting part) of the light reflector, so as to reduce the amount of light directly emitted from the light source and attempt to make the light distribution more even through this technology.

[0006] [Reference 1] Japanese Patent Publication No. 2000-48616 Summary of the Invention

[0007] If the technology disclosed in Reference 1 is adopted, the small holes after surface treatment and other measures, as well as the light-shielding components that constitute them, must be set between the light source and the light-emitting part of the light guide and other components. Therefore, it has disadvantages such as the need for additional parts, high unit price of parts, complicated assembly operations, and high configuration accuracy requirements, which may not meet the needs.

[0008] In view of this situation, the present invention aims to provide a light guide with a simpler construction that can average the light distribution, as well as an illumination device, an image sensor, and a reading device using the light guide.

[0009] To address the aforementioned issues, one embodiment of the light guide of the present invention is a columnar light guide, comprising a light-injecting surface disposed on or near an end face of the light guide, a light-emitting surface disposed on at least a portion of a side face along the long side direction of the light guide, and at least one interface disposed between the light-injecting surface and the light-emitting surface.

[0010] Another embodiment of the present invention is also a light guide. This light guide system, a columnar light guide, includes: a groove provided on or near an end face of the light guide to accommodate at least a portion of a light source; a light-injecting surface within the groove; a light-exiting surface provided on at least a portion of the side faces along the long side direction of the light guide; and at least one interface provided between the light-injecting surface and the light-exiting surface.

[0011] Another aspect of the present invention is a lighting device, which includes the light guide described above, and a light source that directs light from the light-injecting surface into the interior of the light guide.

[0012] Another aspect of the present invention is an image sensor, which includes: the aforementioned illumination device that provides linear illumination to an object, an array of upright equal-magnification lenses that collects reflected light from the object, and a light-receiving element that receives the light collected by the array of upright equal-magnification lenses.

[0013] Another embodiment of the present invention is a reading device, which includes: the aforementioned image sensor, a driving mechanism for scanning the image sensor, and an image processing unit for processing the data read by the image sensor.

[0014] Furthermore, any combination of the above-mentioned constituent elements, or any transformation of the present invention in methods, apparatus, systems, etc., are all valid embodiments of the present invention. Moreover, unless otherwise specified, the term "amount of light" in this specification represents the intensity and magnitude of physical quantities such as light power (operating rate) and energy; in addition, for example, "radiant quantity" includes concepts such as radiant flux, radiant intensity, radiance, irradiance, and radiant energy; and "photometric quantity" includes concepts such as luminous flux, luminous intensity, luminance, and illuminance.

[0015] [Effects of the Invention] The present invention provides a light guide that can average the amount of light with a simpler structure, and an illumination device, an image sensor and a reading device using the light guide. Simple Explanation of the Diagram

[0016] Figures 1(a) to (d) are schematic diagrams illustrating a lighting device of one embodiment of the present invention. Figure 2 is a schematic enlarged cross-sectional view of the lighting device near its light source. Figure 3 is a schematic diagram of the light rays when there is no interface between the first end face and the light emission surface. Figure 4 is a schematic diagram of light rays when there is an interface between the light-incident surface and the light-outceasing surface through a concave portion. Figure 5 is a schematic diagram of one type of texture on a light-reflecting surface. Figure 6 is a schematic diagram of another type of texture on a light-reflecting surface. Figure 7 is a schematic diagram of other textures on the light-reflecting surface. Figure 8 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 9 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 10 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 11 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 12 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figures 13(a) to (d) are schematic diagrams illustrating other embodiments of the lighting device of the present invention. Figure 14 is a schematic enlarged cross-sectional view of the lighting device near its light source. Figure 15 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 16 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 17 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figure 18 is a partial cross-sectional schematic diagram of a light guide including the light source and interface. Figures 19(a) and (b) are schematic diagrams of one example of a light source that houses three LED chips inside a box. Figures 20(a) and (b) are schematic diagrams of a lighting device, which includes a thin circuit board on which the light source is actually installed and a light guide with a flange having a positioning pin. Figures 21(a) to (d) are schematic diagrams illustrating the lighting device used to simulate the first embodiment. Figure 22 is a diagram showing the light distribution (irradiance distribution) along the light emitting surface of the lighting device of the first embodiment. Figure 23 is an enlarged view of L = 0~25mm in Figure 22. Figures 24(a) and (b) are schematic diagrams illustrating a lighting device used to simulate the second embodiment. Figure 25 is a diagram showing the light distribution (irradiance distribution) along the light emitting surface of the lighting device of the second embodiment. Figure 26 is an enlarged view of L = 0~25mm in Figure 25. Figures 27(a) to (d) are schematic diagrams illustrating the lighting device used to simulate the third embodiment. Figure 28 is a diagram showing the light distribution (irradiance distribution) along the light emitting surface of the lighting device of the third embodiment. Figure 29 is an enlarged view of L = 0~25mm in Figure 28. Figures 30(a) to (d) are schematic diagrams illustrating the lighting device used to simulate the fourth embodiment. Figure 31 is a diagram showing the light distribution (irradiance distribution) along the light emitting surface of the lighting device of the fourth embodiment. Figure 32 is an enlarged view of L = 0~25mm in Figure 31. Figure 33 is a schematic cross-sectional view of the reading device using the lighting device of this embodiment. Implementation

[0017] The following description pertains to embodiments of the present invention. The same or equivalent constituent elements, components, and processes shown in the figures will be represented by the same symbols, and repeated descriptions will be omitted where appropriate. Furthermore, the embodiments are merely examples and are not intended to limit the invention; all features and combinations described in the embodiments do not necessarily represent the essence of the invention.

[0018] Figures 1(a) to (d) are schematic views of four sides illustrating an embodiment of the lighting device 10 of the present invention. Figure 1(a) is a schematic view of the left side of the lighting device 10; Figure 1(b) is a schematic plan view of the lighting device 10; Figure 1(c) is a schematic view of the cross section along line AA in the lighting device 10 shown in Figure 1(a); Figure 1(d) is a schematic view of the bottom of the lighting device 10.

[0019] The lighting device 10 has at least one light source 12 and a light guide 14. The light guide 14 is a columnar body extending along the Z direction (also referred to as the long side direction), comprising: a first end face 14a, which is the end face of one end in the Z direction; a light reflecting surface 14b, which is at least one side of the light guide 14 along the Z direction; a light emitting surface 14c, which is opposite to the light reflecting surface 14b and is also a side of the light guide 14 along the Z direction; and a second end face 14d, which is the end face of the other end in the Z direction. In this embodiment, the light source 12 is disposed on the first end face 14a side so that a portion of the light emitted from the light source 12 travels in the Z direction of the light guide 14, or, if the axis of symmetry of the light emitted from the light source 12 is taken as the optical axis, the optical axis can be made parallel to the Z direction. The light emitted from the light source 12 enters the light guide 14 from the first end face 14a, which is the light incident surface, and diffuses, propagating in the Z direction within the light guide 14. Furthermore, the light source is only configured on the first end face 14a side in the figure, but it is also possible to configure the light source on the second end face 14d side at the same time.

[0020] Figure 2 is an enlarged cross-sectional schematic view of the lighting device 10 near the light source 12. In Figure 2, arrows typically indicate light rays emitted from the light source 12 and entering the light guide 14.

[0021] In this embodiment, a recess 16 is formed on the first end face 14a of the light guide 14, which is recessed in the Z direction. This recess 16 is formed on the first end face 14a between the light source 12 and the light emitting surface 14c. In this embodiment, the recess 16 has a rectangular cross-section or top view. Through the arrangement of this recess 16, a plurality of interfaces (first interface 16a, second interface 16b, and third interface 16c) are formed between the first end face 14a, which serves as the light-injection surface, and the light-emitting surface 14c. The first interface 16a is the lower side surface of the recess 16, the second interface 16b is the bottom surface of the recess 16, and the third interface 16c is the upper side surface of the recess 16. Although not specifically shown in Figure 2, the recess 16 may have a pair of opposing interfaces in the Y direction, or the recess 16 may penetrate the light guide in the Y direction. The light guide 14 of this embodiment has a recess 16 that is recessed from the light-injection surface in the Z direction or the long side direction.

[0022] Figure 3 is a schematic diagram showing that when there is no interface between the first end face 14a and the light emitting surface, a portion of the light emitted from the light source 12 goes directly to the light emitting surface 14c. For example, the light that goes directly to the light emitting surface 14c as mentioned above is closely related to the reason why the light intensity increases near the light source 12, resulting in a biased light intensity distribution.

[0023] Figure 4 illustrates the result of the light-incident surface having a recessed portion in the Z direction. When an interface is formed between the light-incident surface (first end face 14a) and the light-outceasing surface 14c through the recess 16, a portion of the light emitted from the light source 12 will pass through the interface and be refracted in a direction farther from the light source 12. One of the reasons for the increased light intensity near the light source 12 when the interface is absent (Figure 3) is present (Figure 4), is that the light intensity will be refracted in a direction farther from the light source 12, reducing the concentration of the light beam near the light source 12. Therefore, the goal of averaging the light intensity distribution across the illumination area can be achieved.

[0024] The light guide 14 of this embodiment has a recessed portion with an interface between the light-injection surface or the light source and the light-emission surface 14c, which can provide an illumination device that can uniformly distribute the light. Furthermore, the term "recessed portion" includes concepts such as holes, grooves, and recesses, and is not limited to a specific cross-sectional shape or top view shape, as long as it can function through the several interfaces constituting the recessed portion to reduce the concentration of light beams near the light source.

[0025] The light guide 14 will be described in detail below. The light guide 14 may be, for example, a unidirectional long rod, bar, or column, into which light entering from the first end face 14a propagates along its longer side within the light guide 14. The vertical cross-section of the light guide 14 in the Z direction is polygonal, slightly circular (including elliptical), or a combination of the aforementioned shapes, and may even include a portion of a curve. The light guide 14 has a plurality of side surfaces extending along its longer side and composed of planar or curved surfaces.

[0026] A portion of the light is reflected more than once on the aforementioned side surface within the light guide 14 and propagates along its long side. At least one side surface of the light guide 14 is a light-emitting surface 14c that emits light in a straight line. Furthermore, the light guide 14 includes a light-reflecting surface 14b opposite the light-emitting surface 14c, which reflects at least a portion of the light propagating within the light guide 14 toward the light-emitting surface 14c. In other words, light emitted from the light source 12 enters the light guide 14 from its first end face 14a, and a portion of this light is reflected within the light guide 14 while propagating along its long side. A portion of the light propagates through the light guide 14 to the light-reflecting surface 14b, and through the light-reflecting surface 14b, another portion of the light reaches the light-emitting surface 14c and exits from the light-emitting surface 14c, thus realizing an illumination device 10 that emits light in a straight line along its long side. The light guide 14 includes a first end face 14a, a light emitting surface 14c, and a light reflecting surface 14b, which can also be integrally formed.

[0027] Assuming the vertical cross-sectional shape of the light guide 14 in the Z direction is set to a circumscribed circle, the diameter of the circumscribed circle can be 1mm to 30mm, and the length in the longitudinal direction can be 50mm to 1200mm. For example, if the lighting device 10 is used in a whiteboard reader, the effective length in the longitudinal direction can reach approximately 1000mm; if the lighting device 10 is used in a multifunction printer or similar device equipped with a reader, the effective length in the longitudinal direction can reach 100mm to 330mm.

[0028] When the light guide 14 is assembled onto components such as a housing for the purpose of assembling the light source 12 or a circuit board mounting the light source 12, or for the purpose of assembling other parts, a blade-shaped flange may be provided near at least one end (e.g., the first end face 14a) of the light guide 14. For example, the flange may be a right-angled surface of the light guide 14 in the long side direction (Z direction), or it may have auxiliary structures such as a locating pin or a notch to improve the positioning accuracy with other parts.

[0029] If the light source 12 or the circuit board on which the light source 12 is mounted is assembled near the first end face 14a of the light guide 14, a groove (recess or cavity, etc.) can be provided on the first end face 14a of the light guide 14 to contain part or all of the light source 12. If the light guide 14 and the light source 12 (e.g., a light-emitting element) are integrally formed, the body of the light source 12 or a part thereof can be housed inside the light guide and roughly sealed, reducing the possibility that the fragile part of the light source 12 is exposed to external air or external interference, thereby extending the life of the component, and also having the advantage of saving space. If the light guide 14 has a groove for housing the light source, the light emitting surface of the light source 12 can be made slightly perpendicular to the long side direction (Z direction) of the light guide 14, or when assembling the light source 12, the optical axis of the light source 12 can be made parallel to the long side direction (Z direction) of the light guide 14, so that the bottom surface of the groove in the long side direction of the light guide 14 becomes the light emitting surface. If we consider the surface from which the light from light source 12 is emitted as the light-emitting surface, the distance between the light-emitting surface of the light source and the light-incident surface of the light guide is 0-5mm, and this distance can also be 0-3mm (except for 0mm). When the distance is 0mm, it means that the light-emitting surface of the light source and the light-incident surface of the light guide are in contact with each other. By slightly separating the light-emitting surface of the light source from the light-incident surface of the light guide, the light-incident surface of the light guide will also play a role in refracting light, which may reduce the concentration of the light beam near the light source to some extent.

[0030] Furthermore, from the perspective of propagation efficiency and illumination efficiency, the light guide 14 is preferably transparent to the wavelengths of light contained in the illumination light, and the material constituting the light guide 14 should absorb as little light as possible. For example, a light guide 14 with a thickness of 10 mm can have an internal transmittance of over 90% at a wavelength of 550 nm, preferably over 95%, and ideally over 98%. Internal transmittance refers to the transmittance of the incident and emitting surfaces excluding surface reflectivity.

[0031] The light guide 14 can be made of resin to meet the requirements of processability and low cost. If the light guide 14 is formed of resin, production efficiency can be improved by methods such as injection molding or casting. Alternatively, the light guide 14 can be formed by combining resin with materials such as metal, ceramic, or glass. For example, the long side portion of the light guide 14 can be formed of transparent resin or glass, while the flange (used for assembling components such as housings or assembling the light source 12 and circuit board) can be formed of metal, ceramic, or opaque resin. Furthermore, if a high-intensity LED or other light source is used as the light source 12, due to its high heat generation, ceramics with high heat dissipation properties, such as alumina, can be used as the material constituting the area near the light source 12.

[0032] The material forming the light guide 14 can be a transparent resin such as a cyclic olefin resin, an acrylic resin, a vinyl chloride resin, an epoxy resin, a PET resin, a PC resin, or a GPPS resin. The light guide 14 can be manufactured using methods such as injection molding, insertion molding, blow molding, or extrusion molding. Alternatively, the light guide 14 can be made by combining metals such as aluminum or duralumin, or ceramic materials such as bauxite or zirconium oxide, with the aforementioned transparent resin.

[0033] Next, the light emitting surface 14c of the light guide 14 will be described in detail. The light emitting surface 14c is provided on at least a portion of the side surface along the long side of the light guide 14, emitting light from inside the light guide 14. The light emitting surface 14c may have a smooth and flat surface, or it may contain a partially curved surface following the shape of the object. Furthermore, if it is necessary to diffuse the emitted light, a plurality of tiny protrusions and depressions can be provided on the surface of the light emitting surface 14c, and it can be processed by sanding, grinding, or other methods to become a so-called diffusion surface. In addition, to improve light transmittance, an anti-reflective film or a low-reflection film can be formed on the surface of the light emitting surface 14c. The anti-reflective film and the low-reflection film can be formed as a dielectric multilayer film by methods such as sputtering and vacuum evaporation, or as a coating made of a low-refractive-index material containing hollow or solid particles. Furthermore, to suppress the emission of light in a certain wavelength range, a light-absorbing film or a light-reflecting film can also be formed on the light emitting surface 14c. For example, a light-absorbing film can be formed by coating a resin containing microparticles or pigments onto the light-emitting surface 14c. These microparticles or pigments can absorb light within a specific wavelength range. A light-reflecting film can be formed by methods such as sputtering and vacuum evaporation to create a dielectric multilayer film.

[0034] Next, the light-reflecting surface 14b of the light guide 14 will be described in detail. The light-reflecting surface 14b is suitably provided with textures that reflect or diffuse light, including but not limited to the following: textured patterns formed on a rough surface; printed textures such as white or silver that reflect light; textures with a diameter ranging from several μm to several mm, such as pits or a portion of a sphere (which appear as water droplet patterns when viewed from above); textures that are concave or convex in shape, such as a cylinder or cone; textures that are concave or convex in shape with their sides spanning the width of the light-reflecting surface; and combinations of the aforementioned textures. The textures can also be formed on the light-reflecting surface 14b considering factors such as the required intensity distribution of the illumination light, the length and size of the illumination device, the shape of the light guide 14, and the light distribution of the light source 12. In addition, the light reflecting surface 14b can also be formed with the same method as the light emitting surface 14c, depending on the purpose and required performance, to form an anti-reflection film, a light absorption film, or a light reflecting film.

[0035] Figures 5-7 show several patterns on the light-reflecting surface 14b. The patterns on the light-reflecting surface 14b of the light guide 14 are not limited to these, and these patterns can be appropriately combined.

[0036] Figure 5 shows a plurality of structures 18 formed on the light-reflecting surface, which, when viewed from above, appear to be slightly rounded in various sizes. The slightly rounded structures 18 can be either concave or convex. As shown in Figure 5, the structures 18 can present as a plurality of concave shapes, such as a portion of a sphere or a curved surface, with diameters ranging from several μm to several mm. The size of the slightly rounded structures 18, for example, can vary in spacing or size as they move further from the light source 12, or they can be randomly arranged.

[0037] Figure 6 shows a plurality of groove-like or ridge-like structures 20 formed on the light-reflecting surface in a direction perpendicular to the Z-direction. Grooves represent depressions, and ridges represent protrusions. As shown in Figure 6, grooves or ridges can be formed in a direction perpendicular to the Z-direction. The spacing or size of these structures 20 can vary with distance from the light source 12, or they can be randomly arranged. For example, the spacing between the groove-like or ridge-like structures 20 formed at a greater distance from the light source 12 can be smaller than that between the structures 20 formed near the light source 12.

[0038] Figure 7 shows the reflective patterns 22 formed on the light-reflecting surface by printing or other methods. Each reflective pattern 22 can be, for example, white or silver with high reflectivity, and its brightness or hue can be changed according to its distance from the light source 12. For example, the reflective patterns 22 formed at a greater distance from the light source 12 can have a higher reflectivity than the reflective patterns 22 formed near the light source 12; or, the reflective patterns 22 formed at a greater distance from the light source 12 can have a larger area than the reflective patterns 22 formed near the light source 12.

[0039] Next, the cover (not shown) covering the light guide 14 will be described. The lighting device 10 may have a cover to cover at least the rod-shaped portion or effective area (the area illuminated by light) of the light guide 14. Light entering the light guide 14 is repeatedly reflected on the side of the light guide 14 and propagates in the long side direction (Z direction) of the light guide 14, but some of the light may escape from the side of the light guide 14. If light escapes from a surface other than the light emitting surface 14c, it will cause loss. Therefore, an additional function can be considered to allow light emitted from a surface other than the light emitting surface 14c to be reflected again within the light guide 14 and return to the side of the light guide 14. The inner structure of the cover can be designed to match the shape of the side of the light guide 14, and in order to improve the reflectivity of the inner side of the cover, it is preferable that at least the inner surface opposite to or in contact with the light guide 14 is white or silver.

[0040] Conversely, a coverless lighting device 10 could also be considered. While a cover would allow it to function, it would increase the cost of the lighting device 10 and components such as the reading device using it. Therefore, if cost reduction is required, a coverless lighting device 10 should be considered. A low-cost lighting device 10 could be a selling point in marketing. When light propagates within the light guide 14, it can achieve total internal reflection through multiple sides. Since total internal reflection or high reflectivity occurs when the angle of incidence of light relative to the surface increases, by thinning the rod portion of the light guide 14 (reducing the diameter of the circumscribed circle of the cross-section of the light guide 14) and using a material with a high refractive index, the amount of light escaping from sides other than the light emitting surface 14c can be reduced, thereby increasing the propagation rate. The effective length of the light guide 14 is either the length required to illuminate the target object (the length of a specific side of the target object) or the length that ensures the required light intensity is consistent. Furthermore, the effective length of the light guide 14 can be 85% to 100% of the total length of its long rod-shaped portion. In addition, the surface of the light guide 14 other than the light emitting surface can be partially or entirely colored with a color that is expected to improve light reflectivity, such as white or silver, but is not limited to this.

[0041] In addition, if the light guide 14 is fixed to the housing as described later, and the housing has a surface that is opposite to the side of the light guide 14 except for the light emitting surface 14c, then this surface can be designed to be a color with high reflectivity, such as white or silver, to supplement the function of the cover mentioned above.

[0042] Next, the interface formed by the recess 16 will be described in detail. In the light guide 14 of this embodiment, there is at least one interface between the light-injecting surface and the light-emission surface 14c. In addition, there is at least one interface on the light path from the light-injecting surface to the light-emission surface 14c. The fact that the amount of light near the light source 12 is higher than that in other parts (the brightness near the light source 12 is brighter than that in other parts) has always been a problem of the light guide 14. When the inventors of the present invention were working to solve this problem, they were inspired by the following: by providing an interface between the light source 12 and the light-emission surface 14c, a portion of the light emitted from the light source 12 can be refracted or scattered, thereby reducing the amount of light near the light source 12.

[0043] LEDs, commonly used as light sources 12, generally have a Lambertian distribution, allowing light to be emitted at angles of 70° or 80°. If such LEDs are positioned near the first end face 14a of the light guide 14, some of the light will not propagate along the long side of the light guide 14, but will instead directly reach the light emission surface 14c and be emitted. Light following this path is generated in particularly large quantities near the light source 12, increasing the amount of light around it. Through the interface between the light-injection surface and the light-emission surface 14c, light that was originally directed towards the light emission surface 14c undergoes reflection, refraction, and diffusion at a greater distance from the light source due to the interface between the light guide 14 and the air, thereby reducing the amount of light near the light source 12.

[0044] Figures 8 to 12 are partial cross-sectional schematic views of a light guide 14 including a light source 12 and an interface. In each figure, the light source 12 is arranged at the end of the light guide 14, and the first end face 14a of the light guide 14 is the light incident surface.

[0045] As shown in Figure 8, the light guide 14 has a recess 16 extending from the first end face 14a towards the Z direction. The surface of the recess 16 closest to the light reflecting surface (lower side) is the first interface 16a, the surface of the recess 16 deeper in the Z direction (bottom surface) is the second interface 16b, and the surface of the recess 16 closest to the light emitting surface (upper side) is the third interface 16c. Because two or three interfaces are created on the light path from the light source 12 towards the light emitting surface 14c, the light is refracted in a direction farther from the light source, reducing the amount of light reaching the light emitting surface 14c near the light source 12. Therefore, the amount of light emitted from the light emitting surface 14c near the light source 12 is reduced.

[0046] Figures 9 and 10 show that the light guide 14 has a so-called wedge-shaped recess 16 in the Z direction from the first end face 14a, forming a plurality of interfaces. In the light guide 14 shown in Figures 9 and 10, the inclined interface 16d in particular tends to have a critical angle or close to a critical angle with the light rays advancing from the light source 12 to the light emission surface 14c, which can increase the light rays refracted at the interface, and thus more effectively reduce the amount of light emitted from the light emission surface 14c near the light source 12.

[0047] Figure 11 shows a plurality of recesses 16 arranged in the X direction of the light guide 14. Through the light guide 14 shown in Figure 11, the interface can be increased so that the light emitted from the light source 12 and traveling toward the light emission surface 14c can be refracted, thus effectively reducing the amount of light emitted from the light emission surface 14c near the light source 12.

[0048] Figure 12 shows that a portion of the light guide 14 near the light source 12 forms an inclined surface 16e. The light guide 14 shown in Figure 12 is the same as the light guide 14 shown in Figures 9 and 10. The light rays advancing from the light source 12 towards the light emission surface 14c easily have a critical angle or close to the critical angle with the inclined surface 16e, which can increase the light refracted at the interface. Therefore, the amount of light emitted from the light emission surface 14c near the light source 12 can be effectively reduced.

[0049] The recess 16, which contains a plurality of interfaces, can have a cross-section parallel to the X direction (perpendicular to the Z direction) that is polygonal, such as a triangle or quadrilateral, or it can be wedge-shaped or stepped. Furthermore, the interfaces constituting the recess 16 can also be uneven surfaces.

[0050] The recess 16 formed on the first end face 14a toward the long side of the light guide 14 can be filled with resin of a color such as black or white, or a black or white coating film can be formed on the surface constituting the recess 16.

[0051] Figures 13(a) to 13(d) are schematic diagrams illustrating other embodiments of the lighting device 30 of the present invention. Figure 13(a) is a schematic left side view of the lighting device 30. Figure 13(b) is a schematic plan view of the lighting device 30. Figure 13(c) is a schematic cross-sectional view of the lighting device 30 shown in Figure 13(a) along line BB. Figure 13(d) is a schematic bottom view of the lighting device 30. Figure 14 is an enlarged schematic cross-sectional view of the lighting device 30 near the light source 12.

[0052] In this embodiment, a groove 32 is formed on the first end face 14a of the light guide 14. It is advantageous to provide a groove 32 for housing the light source on the end face of the light guide 14 if the light source 12 is positioned on or near the end face of the light guide 14. When the light source 12, such as an LED element, is housed in the groove 32, it is easier to seal off the area near the light source 12, thereby protecting the light source 12 from external interference.

[0053] In this embodiment, the recess 16, which includes a plurality of interfaces (first interface 16a, second interface 16b, and third interface 16c), is formed from the first end face 14a of the light guide 14 along the long side of the light guide 14, and extends further inward than the bottom surface 32a of the groove 32. The surface of the light source 12 opposite to the bottom surface 32a of the groove 32 is the emission surface of the light source 12. Furthermore, note that in the lighting device 30 of this embodiment, the light guide 14 has a flange 34, which includes a surface perpendicular to the Z direction near the first end face 14a. Even in this embodiment, where the first end face 14a of the light guide 14 has a groove 32 for receiving the light source, its function and effect are the same as in the form without the groove 32 (see Figure 1). In this embodiment, when the light source 12 emits light centered on the Z direction, the bottom surface 32a of the groove 32 is the light-injection surface, which is easily understood. The distance between the light emitting surface of the light source 12 and the light incident surface (of the light guide) can be 0~5mm or 0~3mm (except 0mm).

[0054] Figures 15-18 are partial cross-sectional schematic diagrams of the light guide 14, which has a light source 12 housed in a groove and a recess containing an interface.

[0055] Figure 15 shows that the light guide 14 has a so-called wedge-shaped recess 16 in the Z direction on the first end face 14a, thus forming a plurality of interfaces. In the light guide 14 shown in Figure 15, the obliquely inclined interface 16d in particular tends to have a critical angle or close to a critical angle with the light rays traveling from the light source 12 to the light emission surface 14c, which can increase the light rays refracted at the interface and thus more effectively reduce the amount of light near the light source 12.

[0056] Figure 16 shows a plurality of recesses 16 arranged in the X direction of the light guide 14. Through the light guide 14 shown in Figure 16, the interface can be increased so that light emitted from the light source 12 and advancing toward the light emission surface 14c can be refracted, thus effectively reducing the amount of light near the light source 12.

[0057] Figures 17 and 18 show that the light guide 14 has an extended recess 16 extending in the Z direction from the bottom surface 32a (light incident surface) of the groove 32. As mentioned above, the recess 16, which includes an interface, can also reduce the amount of light near the light source 12.

[0058] Next, the light source 12 will be described in detail. The light source 12 is disposed near the end face of the light guide 14, so that the light emitted from the light source 12 enters the light guide through the end face of the rod-shaped light guide 14 (or its bottom surface 32a if a groove 32 for receiving the light source is provided). The light source 12 can be disposed on or near the end face of one end of the light guide 14 (e.g., the first end face 14a), or on or near the end faces of both ends of the light guide 14 (the first end face 14a and the second end face 14d).

[0059] The light source 12 can be a light source (such as a light bulb) that emits light by energizing components such as light-emitting diodes (LEDs) and filaments. LEDs are particularly effective because they are small, energy-efficient, produce a large amount of light, and can reproduce various colors. If LEDs are used as the light source 12, for example, a plurality of LEDs that emit light of wavelengths R (red), G (green), and B (blue) and contain at least three chips can be used. In this case, by appropriately adjusting the wavelength and intensity, light that appears white to the naked eye can be emitted, making it suitable as a light source for image sensors and reading devices.

[0060] Figures 19(a) and 19(b) are schematic diagrams of one example of the light source 12, which houses three LED chips 40 within a housing 42. Figure 19(a) is a schematic front view of the light source 12; Figure 19(b) is a schematic cross-sectional view of the light source 12 shown in Figure 19(a) along the CC line. Furthermore, the interior of the housing 42 containing the LED chips 40 may also be filled with transparent resin. As described above, the light source 12 composed of LEDs can be considered to have a light-emitting surface 42a on the end face of the housing 42.

[0061] In this way, LED chips that emit RGB light can be integrated into a single white LED for use as light source 12. Alternatively, if one or two of the RGB LED chips are made inert (non-emitting), light can be emitted in any of the three colors other than white, or in a mixture of those colors. Furthermore, since the light intensity of each RGB LED chip differs, their relative position and phase configuration parameters with the light guide can be optimized based on the required performance of the lighting device, taking into account their intensity.

[0062] Furthermore, LEDs that emit white light can be single-chip LEDs containing resins with blue LEDs and yellow phosphors, or single-chip LEDs containing resins with blue LEDs and red and green phosphors.

[0063] In addition, regarding the actual mounting type of LED, thin substrate-type LEDs that can be actually mounted on the surface or PLCC (Plastic Leaded Chip Carrier) type LEDs can be used, but are not limited to these.

[0064] The light source 12, composed of LEDs or similar types, can be formed on a substrate (circuit board) with a driving circuit. The circuit board can be a rigid substrate or a flexible substrate. Rigid substrates are suitable for structures requiring strength due to their rigidity. Flexible substrates are thin and inexpensive; their low rigidity can be solved by fixing them to a light guide and forming them as a single unit. The substrate can be made from materials such as phenolic resins, epoxy resins, polyimide resins, fluorinated resins, PRO resins, polyimide films, and PET films, or it can be formed from a composite substrate containing materials such as paper, glass fiber, or cloth.

[0065] Figures 20(a) and 20(b) are schematic diagrams of an illumination device 50, which includes a thin circuit board 51 on which a light source 12 is actually mounted and a light guide 14 with a flange 34 having a positioning pin 52. Figure 20(a) is a schematic left side view of the illumination device 50. Figure 20(b) is a schematic cross-sectional view of the illumination device 50 shown in Figure 20(a) along the DD line segment. The flange 34 of the illumination device 50 has a protruding positioning pin 52. Furthermore, a hole 53 is formed on the circuit board 51 for the positioning pin 52 to pass through, and the light source 12 is pre-positioned at a specific position relative to the hole 53. By using the positioning pin 52 and the hole 53 as described above, the correct position of the light source 12 relative to the light guide 14 can be determined.

[0066] The circuit board 51 may have electrodes 54 for power supply to drive the light source. If a flexible circuit board 51 is used, it can be easily assembled into a housing that constitutes a contact image sensor, or connected, fixed, or packaged into other circuit boards.

[0067] The following describes specific embodiments of the present invention.

[0068] <First Embodiment> In this embodiment, a light guide 14 with at least one interface between the light incident surface and the light exit surface 14c is used to simulate and determine how to improve the deviation of the light quantity distribution of the lighting device in the Z direction (the long side direction of the light guide 14).

[0069] Figures 21(a) to 21(d) are schematic diagrams illustrating the lighting device 60 used to simulate the first embodiment. Figure 21(a) is a schematic left side view of the lighting device 60 of the first embodiment. Figure 21(b) is a schematic plan view of the lighting device 60 of the first embodiment. Figure 21(c) is a schematic cross-sectional view of the lighting device 60 of the first embodiment shown in Figure 21(a) along the line EE. Figure 21(d) is a schematic bottom view of the lighting device 60 of the first embodiment.

[0070] Assume the light guide 14 is a quadrangular prism extending in the Z direction, with an end face parallel to the XY plane and four sides perpendicular to the end face. The upper side parallel to the YZ plane is the light emitting surface 14c, and the lower side opposite it is the light reflecting surface 14b. The material of the light guide 14 does not absorb light, and its refractive index for the wavelength used is 1.49. The periphery of the lighting device 60 is air, with a refractive index of 1. The end face of the light guide 14 is parallel to the XY plane, wg = hg = 3.0 mm, the total length Lg = 227.5 mm, and the effective length at the light emitting surface 14c is Lef = 225.5 mm.

[0071] As shown in Figure 21, the light guide 14 has a recess 16 between the location of the light source 12 on the first end face 14a and the light exit surface 14c. The recess 16 is roughly cuboid in shape and has two interfaces perpendicular to and opposite to the X direction, one interface perpendicular to the Z direction, and two interfaces perpendicular to and opposite to the Y direction. The dimension of the recess 16 in the X direction is hc = 0.5 mm, and the dimension in the Y direction is wc = 2.4 mm. dc is the longest distance (depth or protrusion) in the Z direction from the light entry surface of the light guide 14 (i.e., the first end face 14a) to the recess 16. The variation of the dc value will be used as a parameter in the simulation described later.

[0072] The light-reflecting surface 14b of the light guide 14 has a plurality of concave grooves 62 that are perpendicular to the Z direction and have a triangular cross-section, arranged along the Z direction. Generally speaking, the arrangement pitch is larger near the light source 12 and smaller further away from the light source 12. The side surface other than the light-reflecting surface 14b (including the light-emitting surface 14c) is planar.

[0073] On all surfaces of the light guide 14, wherever light reaches, the Snell's law of refraction is strictly applied, and in reality, no light is scattered or absorbed.

[0074] Assuming the light source 12 is an LED, and the light emission surface of the light source 12 is parallel to the XY plane, ws = hs = 1.5mm, the light with symmetrical optical axis and Lambertian distribution is emitted in a single direction. When the light distribution is based on the axis of symmetry, the light source 12 is positioned on the first end face 14a of the light guide 14, so that the optical axis is parallel to the Z direction and coincides with the central axis passing through the center of the light guide 14.

[0075] The simulation used TracePro (Ver. 20.4), a lighting design, analysis, and optimization software from Lambda Research Corporation. The light emitted from light source 12 has a wavelength of 550nm, a total of 1×10⁶ rays, and the aforementioned light distribution. Furthermore, the number of light rays per unit area incident from the light-emitting surface 14c of the light guide at a distance of 4.78mm in the X direction was calculated as the irradiance. It should be noted that the aforementioned example is intended to demonstrate the effectiveness of the recess (interface); in actual implementation on a machine, optimization is required based on the shape of the light guide, the characteristics of the light-reflecting surface, and other specifications.

[0076] The light distribution of the illumination device 60 in the first embodiment is evaluated as the irradiance distribution along the light emission surface 14c. Figures 22 and 23 are graphs of irradiance ratio, where the horizontal axis represents the distance in the Z direction of the effective length Lef of the light guide 14 when the lower limit on the light source side is 0, and the irradiance ratio is obtained by dividing the irradiance at a certain position by the average irradiance over the entire effective length. In this embodiment, the irradiance ratio is preferably 10 or less over the entire effective length, more preferably 6 or less, and ideally 4 or less. Figure 23 is an enlarged view of L = 0~25mm in Figure 22. Figures 22 and 23 show the irradiance ratio of the comparative example without the recess 16 (interface), the irradiance ratio when dc = 0.60mm, the irradiance ratio when dc = 1.30mm, and the irradiance ratio when dc = 2.00mm.

[0077] As shown in Figures 22 and 23, the Z-value of the irradiance ratio will almost always be in the range of approximately 12.5 mm, the same for each extension (dc). On the other hand, when the Z-value is below 12.5 mm, the irradiance ratio will increase if there is no recess 16 with an attached interface, or if dc is too large. However, when dc = 0.6 mm, the irradiance ratio is below 6, and it is expected to have good irradiance distribution (light intensity distribution) illumination characteristics. When the extension (dc) is within an appropriate range, the bottom surface (second interface 16b) of the recess 16 in the Z direction will cause a portion of the light to be refracted in a direction farther from the light emitting surface 14c, thus suppressing the irradiance reaching the light emitting surface near the light source 12. This can be inferred. At this time, the extension (depth) dc of the recess relative to the light incident surface is 0.1 mm, preferably 0.3 mm, and ideally 0.4 mm. Furthermore, the DC thickness should be below 1.0mm, preferably below 0.9mm, and ideally below 0.8mm.

[0078] <Second Embodiment> Figures 24(a) and 24(b) are schematic diagrams illustrating the lighting device 70 used to simulate the second embodiment. Figure 24(a) is a schematic left side view of the lighting device 70 of the second embodiment. Figure 24(b) is a schematic cross-sectional view of the lighting device 70 of the second embodiment shown in Figure 24(a) along the line segment FF.

[0079] The lighting device 70 of the second embodiment differs from the lighting device 60 of the first embodiment in that the end of the recess 16 of the light guide 14 is wedge-shaped in the Z direction. In addition, the conditions and methods for simulating the state, size, etc. are the same as those of the first embodiment.

[0080] The light distribution of the illumination device 70 in the second embodiment is evaluated as the irradiance distribution along the light emission surface 14c. Figures 25 and 26 are graphs of irradiance ratio, where the horizontal axis represents the distance in the Z direction of the effective length Lef of the light guide 14 when the lower limit on the light source side is 0, and the irradiance ratio is obtained by dividing the irradiance at a certain position by the average irradiance over the entire effective length. In this embodiment, the irradiance ratio is preferably 10 or less over the entire effective length, more preferably 6 or less, and ideally 4 or less. Figure 26 is an enlarged view of L = 0~25mm in Figure 25. Figures 25 and 26 show the irradiance ratios of comparative examples without recesses (interfaces), as well as the irradiance ratios for the following cases: assuming the protrusion of the recess in the Z direction is dc, and the end angle of the wedge shape at the end of the recess (the angle between the YZ plane and the inclined plane) is θc, representing the irradiance ratios when (dc, θc) = (2.00 mm, 30°), (1.50 mm, 30°), and (1.50 mm, 19°), respectively.

[0081] As can be seen from Figures 25 and 26, for each extension (dc), the associated irradiance ratio Z value will almost certainly be in the range of approximately exceeding 12.5 mm. On the other hand, when the Z value is below 12.5 mm, and there is no recess 16 with an attached interface, the light intensity will increase. However, when the extension (dc) is 1.50 mm or the end angle (θc) is 30° or less (19°), the irradiance ratio no longer increases but is suppressed, and it is expected to obtain lighting characteristics with good irradiance distribution (light intensity distribution). In the second embodiment, since the end of the recess 16 at its depth in the Z direction is wedge-shaped, the light will reach the interface obliquely oriented relative to the Z direction with a large incident angle. By increasing the reflectivity of this interface, the associated irradiance of the light rays that directly propagate toward the light emission surface 14c near the light source 12 will be reduced, which can be inferred. θc is preferably below 26°, and more preferably below 22°. Furthermore, θc should ideally be above 15°, with 16° being the best.

[0082] <Third Embodiment> Figures 27(a) to 27(d) are schematic diagrams illustrating the lighting device 80 used to simulate the third embodiment. Figure 27(a) is a schematic left side view of the lighting device 80 of the third embodiment. Figure 27(b) is a schematic plan view of the lighting device 80 of the third embodiment. Figure 27(c) is a schematic cross-sectional view of the lighting device 80 of the third embodiment shown in Figure 27(a) along the GG line segment. Figure 27(d) is a schematic bottom view of the lighting device 80 of the third embodiment.

[0083] The lighting device 80 of the third embodiment has a flange 34 near the first end face 14a of the light guide 14. The flange surface, parallel to the XY plane, has dimensions wf = hf = 3.50 mm, and the thickness of the flange in the Z direction is tf = 2.90 mm. Furthermore, the lighting device 80 of the third embodiment has a groove 32 on the first end face 14a of the light guide 14, which houses the light emitting surface of the light source 12. The distance between the light emitting surface of the light source 12 and the light incident surface of the light guide 14 (i.e., the bottom surface of the groove 32) is 0.10 mm.

[0084] The light distribution of the lighting device 80 in the third embodiment is evaluated as the irradiance distribution along the light emission surface 14c. Figures 28 and 29 are graphs of irradiance ratio, where the horizontal axis represents the distance in the Z direction of the effective length Lef of the light guide 14 when the lower limit on the light source side is 0, and the irradiance ratio is obtained by dividing the irradiance at a certain position by the average irradiance of the entire effective length. In this embodiment, the irradiance ratio is preferably 10 or less over the entire effective length, more preferably 6 or less, and ideally 4 or less. Figure 29 is an enlarged view of L = 0~25mm in Figure 28. Figures 28 and 29 show the irradiance ratio of a comparative example without a recess (interface), and the irradiance ratio in the following case: assuming the maximum distance (depth or protrusion) in the Z direction from the light injection surface of the light guide 14 to the recess 16 is dc, where dc is the irradiance ratio at 2.00mm, 1.30mm, and 0.60mm, respectively.

[0085] As can be seen from Figures 28 and 29, similar to the extension (dc), the Z value of the irradiance ratio is almost always in the range of approximately exceeding 12.5 mm. On the other hand, when the Z value is below 12.5 mm, the irradiance ratios of all examples are of a good level of less than 6, and the maximum irradiance ratios when the extension (dc) is 1.30 mm and 2.00 mm are also around 1, exhibiting lighting characteristics with better irradiance distribution (light intensity distribution).

[0086] In the third embodiment, light rays are emitted from or near the flange 34, particularly near the junction between the flange 34 and the rod-shaped portion extending towards the long side of the light guide 14, and reach the effective illumination range. Therefore, the result tends to differ from the first or second embodiment without the flange. When the extension is 1.30 mm or 2.00 mm, it can be inferred that it is sometimes difficult to obtain sufficient irradiance to provide illumination in the range of Z from 0 to 12.5 mm. However, for example, by moving the starting point of the effective length of the light emitting surface 14c about 10 mm in the Z direction, an average irradiance distribution (light intensity distribution) can be obtained along the entire effective length of the light emitting surface 14c. This can also be inferred.

[0087] <Fourth Embodiment> Figures 30(a) to 30(d) are schematic diagrams illustrating the lighting device 90 used to simulate the fourth embodiment. Figure 30(a) is a schematic left side view of the lighting device 90 of the fourth embodiment. Figure 30(b) is a schematic plan view of the lighting device 90 of the fourth embodiment. Figure 30(c) is a schematic cross-sectional view of the lighting device 90 of the fourth embodiment shown in Figure 30(a) along the HH line segment. Figure 30(d) is a schematic bottom view of the lighting device 90 of the fourth embodiment.

[0088] The lighting device 90 of the fourth embodiment is the same as that of the third embodiment except that the end of the recess 16 in the Z direction is wedge-shaped.

[0089] The light distribution of the lighting device 90 in the fourth embodiment is evaluated as the irradiance distribution along the light emission surface 14c. Figures 31 and 32 are graphs of irradiance ratio, where the horizontal axis represents the distance in the Z direction of the effective length Lef of the light guide 14 when the lower limit on the light source side is 0, and the irradiance ratio is obtained by dividing the irradiance at a certain position by the average irradiance over the entire effective length. In this embodiment, the irradiance ratio is preferably 10 or less over the entire effective length, more preferably 6 or less, and ideally 4 or less. Figure 32 is an enlarged view of L = 0~25mm in Figure 31. Figures 31 and 32 show the irradiance ratios of comparative examples without a recess (interface), and the irradiance ratios for the following cases: assuming the protrusion of the recess in the Z direction is dc, and the end angle of the wedge shape at the end of the recess (the angle between the YZ plane and the inclined plane) is θc, the irradiance ratios for (dc, θc) = (2.00 mm, 30°), (1.50 mm, 30°), and (1.50 mm, 19°) are respectively.

[0090] As can be seen from Figures 31 and 32, for each extension (dc), the Z value of the irradiance ratio will almost always be in the range of approximately exceeding 12.5 mm. On the other hand, when the Z value is below 12.5 mm and there is no recess 16 with an attached interface, the irradiance ratio will increase. However, when the extension (dc) is 1.50 mm or the end angle (θc) is 30° or smaller (19°), the irradiance ratio no longer increases but is suppressed, and it is expected to obtain lighting characteristics with good irradiance distribution (light intensity distribution). In the fourth embodiment, since the end of the recess 16 at its depth in the Z direction is wedge-shaped, light will reach the interface that is oblique to the Z direction with a large incident angle. By increasing the reflectivity of this interface, it can be inferred that the irradiance of light rays that travel directly toward the light emission surface 14c near the light source 12 will be reduced.

[0091] Figure 33 is a schematic cross-sectional view of the reading device 100 using the lighting device 10 of this embodiment. The reading device 100 includes: a contact plate 102 for placing the object to be read (original) 120, an image sensor (close-fitting image sensor) 104, a drive mechanism 116 for scanning the image sensor 104, and an image processing unit 118 for processing the data read through the image sensor 104. The reading device 100 uses the drive mechanism 116 to move the image sensor 104 in a direction parallel to the contact plate 102, thereby scanning part or all of the original 120 and reading information from the original 120.

[0092] The image sensor 104 includes an illumination device 106 that illuminates the original 120 in a straight line (perpendicular to the longitudinal direction of the paper), an upright magnifying lens array 108 that collects the light reflected from the original 120 using an upright magnifying optical system, a light receiving element 110 that receives the collected light and is arranged in an array, a circuit board 112 that mounts the light receiving element 110, the illumination device 106, and a housing 114 that houses and fixes the upright magnifying lens array 108 and the light receiving element 110 in a specific configuration.

[0093] The lighting device 106 can use the lighting device described in the above embodiment. As long as a lighting device that can even out the light distribution is used, as in the above embodiment, a high-quality reading device 100 can be achieved.

[0094] The above description pertains to embodiments of the present invention. It will be understood by those skilled in the art that the above embodiments are merely examples, and various variations can be made to the combination of each constituent element and each processing step, all of which are included within the scope of protection of the present invention.

[0095] 10, 30, 50, 60, 70, 80, 90: lighting device 12: Light source 14: Light guide 14a: First end face 14b: Light reflecting surface 14c: Light-emitting surface 14d: Second end face 16: concave part 16a: First Interface 16b: Second Interface 16c: Third Interface 16d: Interface 18: Structures 100: Reading device 102: Contact plate 104: Image Sensor 106:Lighting device 108: Upright equal-magnification lens array 110: Light receiving element 112: Circuit board 114: Shell 116: Drive mechanism 118: Image Processing Department 120:Original manuscript 20: Structures 22: Reflection pattern 32: Groove 32a: Bottom surface 34: Flange 40: LED chip 42: Box 42a: Light emission surface 51: Circuit board 52: Positioning pin 53: Kong 54: Electrode 62: concave groove

Claims

1. A columnar light guide, comprising: a light-incident surface disposed on or near one end face of the light guide; a light-exiting surface disposed on at least a portion of a side surface along the long side direction of the light guide; and at least one interface disposed between the light-incident surface and the light-exiting surface; wherein, The end face has a flat portion perpendicular to the long side direction of the light guide between the light injection surface and the light emission surface; the flat portion has a recessed portion that is recessed from the end face toward the long side direction of the light guide; the interface is provided in the surface included by the recessed portion.

2. The light guide as described in claim 1, wherein at least one light-reflecting surface is provided on one side along the long side of the light guide, the light-reflecting surface being disposed on the portion opposite to the light-emitting surface.

3. The light guide as described in claim 1 or 2, wherein the cross-section of the recess perpendicular to the long side of the light guide has a polygonal shape.

4. The light guide as described in claim 1 or 2, wherein the recess has a wedge shape in the cross section perpendicular to the long side direction of the light guide.

5. The light guide as described in claim 1 or 2, having a plurality of the recesses on the end face.

6. The light guide as described in claim 1 or 2, having a groove on its end face for receiving at least a portion of the light source.

7. A columnar light guide comprising: a groove disposed on or near one end face of the light guide, for receiving at least a portion of a light source; a light-injecting surface disposed within the groove; a light-exiting surface disposed on at least a portion of the side surface along the long side of the light guide; and at least one interface disposed between the light-injecting surface and the light-exiting surface; wherein, The end face has a flat portion perpendicular to the long side direction of the light guide between the light injection surface and the light emission surface; the flat portion has a recessed portion that is recessed from the end face toward the long side direction of the light guide; the interface is provided in the surface included by the recessed portion.

8. The light guide as described in claim 1, 2 or 7 has a flange formed near the end face.

9. A lighting device comprising: a light guide as described in claims 1, 2 or 7; and a light source that directs light into the interior of the light guide from the light-incident surface.

10. An image sensor comprising: an illumination device as described in claim 9, providing linear illumination to an object; a vertical equal-magnification lens array for collecting reflected light from the object; and a light-receiving element for receiving the light collected by the vertical equal-magnification lens array.

11. A reading device comprising: an image sensor as described in claim 10; a drive mechanism for scanning the image sensor; and an image processing unit for processing data read through the image sensor.

Images