Patent Publication Number: US-2021190295-A1

Title: Light irradiation device

Description:
TECHNICAL FIELD 
     The present invention relates to a light irradiation device. 
     BACKGROUND ART 
     For example, Patent Reference 1 discloses a multibeam scanning device that uses a refraction optical system including a combination of two wedge prisms whose wedge directions are opposite to each other. One of the prisms is rotated relative to the other so as to adjust the direction of a light beam. 
     PRIOR ART REFERENCE 
     Patent Reference 
     Patent Reference 1: Japanese Patent Application Publication No. 2002-174785 (paragraphs 0011, 0045, and FIG. 3) 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     However, each wedge prism of the multibeam scanning device described in Patent Reference 1 has a combination of two planes. Thus, light passing through the wedge prisms has aberration. In particular, the influence of the aberration is noticeable when a light source such as a surface-emitting LED is used. Accordingly, large aberration occurs. As a result, a contour of irradiation light is blurred on a surface irradiated with the light. 
     Means of Solving the Problem 
     A light irradiation device according to the present invention includes a light source to emit light, a projection optical system to project an image formed based on the light emitted from the light source, an aberration correction surface to correct an aberration occurring when the image is projected by the projection optical system, a first wedge prism to receive and deflect the light emitted from the projection optical system, and a second wedge prism to receive and deflect the light deflected by the first wedge prism. The first wedge prism and the second wedge prism are held so that a deflection direction of light emitted from the second wedge prism is changed by rotation of at least one of the first wedge prism and the second wedge prism. The aberration correction surface is located on the first wedge prism side with respect to an emission surface of the projection optical system, and is located on the projection optical system side, with respect to the first wedge prism, including an incident surface of the first wedge prism. 
     Effects of the Invention 
     With the light irradiation device according to the present invention, it is possible to reduce aberration that occurs when light is deflected by a pair of wedge prisms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view schematically illustrating a configuration of a light irradiation device  100  according to a first embodiment of the present invention. 
         FIG. 2  is a view illustrating a spot diagram of the light irradiation device  100  according to the first embodiment of the present invention. 
         FIG. 3  is a diagram showing evaluation points on a light-emitting surface  101  according to the first embodiment of the present invention. 
         FIG. 4  is a view schematically illustrating a configuration of a light irradiation device  200  according to a comparative example. 
         FIG. 5  is a view illustrating a spot diagram of the light irradiation device  200  according to the comparative example. 
         FIG. 6  is a view illustrating a configuration of a light irradiation device  300  according to a modification of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     From the viewpoint of reducing environmental load, such as reducing emission of carbon dioxide (CO 2 ) and consumption of fuel, it is desired to save energy of light irradiation devices. Accordingly, downsizing, weight reduction, and power saving of the light irradiation devices are required. In view of this, as a light source for the light irradiation device, it is desired to employ a semiconductor light source exhibiting higher light-emission efficiency than a conventional halogen bulb (lamp light source). Examples of the “semiconductor light source” include a light-emitting diode (LED), a laser diode (LD) and the like. 
     A light source such as a light source using an organic electroluminescence (organic EL), a light source using a phosphor, or the like is referred to as a solid light source. As to the light source using a phosphor, the phosphor coated on, for example, a base material is irradiated with excitation light so that the phosphor emits light. The semiconductor light source is one of the solid light source. 
     A wedge prism is a prism having an emission surface which is tilted with respect to an incident surface. That is, the wedge prism includes a tilted optical surface. One surface of the wedge prism is tilted by a small angle with respect to the other surface. A tilt angle of one surface with respect to the other surface is referred to as a wedge angle or an apex angle. Light incident on the wedge prism is refracted at an angle in accordance with the apex angle and is emitted. Light incident on the wedge prism is refracted in a direction toward a side in which the prism has a larger thickness. An angle of light emitted from the wedge prism with respect to light incident on the wedge prism is referred to as a deflection angle. 
     In the following description, the apex angle will be referred to as a wedge angle α. Although two refraction surfaces of the wedge prism are generally flat surfaces, a “wedge prism” described below includes a prism having at least one refraction surface which is a curved surface. 
     In the following embodiment, one surface of the wedge prism is a surface perpendicular to a rotation axis. Alternatively, two surfaces of the wedge prism may be tilted with respect to the rotation axis. That is, an incident surface and an emission surface of the wedge prism may be tilted with respect to the rotation axis. 
     In a device that deflects light by using two wedge prisms such as the multibeam scanning device of Patent Reference 1, light emitted from the wedge prisms is irradiated onto a circular area on an irradiation surface. 
     The two wedge prisms are rotated about the rotation axis of the wedge prisms so that the deflection direction of light emitted from the wedge prisms is changed. For example, when the two wedge prisms are rotated in opposite directions by the same angle, light emitted from the wedge prisms moves along a straight line on the irradiation surface. That is, light emitted from the wedge prisms moves linearly in a direction perpendicular to the rotation axis of the wedge prisms. Light emitted from the wedge prisms moves linearly on the irradiation surface in a direction perpendicular to the rotation axis of the wedge prisms. 
     A device that deflects light by using two wedge prisms is employed in, for example, an apparatus that forms an image or displays information by scanning with a light beam having a small beam diameter such as laser light. However, a light irradiation device  100  is employed in, for example, an illumination device or the like that changes light distribution by scanning with a light beam having a larger beam diameter such as a light beam of an LED. 
     The light irradiation device  100  is employed in an apparatus that displays a projected image while moving the projected image on an irradiation surface. For example, an image display device is disposed on a light path of the light irradiation device  100 . The image display device is a diaphragm plate having a shape of a symbol or the like, a liquid crystal panel, or the like. Accordingly, the light irradiation device  100  is capable of moving a projected image of the symbol, the image or the like on the irradiation surface. In this manner, the light irradiation device  100  is capable of projecting image information on a road surface, a passage or the like to attract attention, to guide a passenger or for other purposes. 
     The light irradiation device  100  is also applicable to, for example, a downlight, a spotlight, a searchlight, or a vehicle lighting device. 
     The downlight is a small lighting appliance that is buried in and attached to a ceiling in a building. The light irradiation device  100  is capable of moving an irradiation area of the downlight. Further, the downlight is capable of projecting a projected image. 
     The spotlight is one of lighting appliances devised to throw strong light intensively on a specific place. The spotlight is a lighting appliance used mainly in a theater or the like for attracting attention of an audience, and is configured to intensively illuminate one spot. The spotlight is used while moving an irradiated position when an irradiation target moves. 
     The searchlight is an illumination device configured to illuminate a distant place at nighttime. The searchlight is generally mounted to an altazimuth mount swingable vertically and laterally. The light irradiation device  100  is capable of moving an irradiation area without using the altazimuth mount. 
     The light irradiation device  100  serves as a vehicle lighting device and can be used as a high beam headlight which is an illumination device of a vehicle such as an automobile or the like. The high beam headlight is a headlight that is used during traveling. An illumination distance of the high beam headlight is, for example, 100 m. For example, in order to illuminate a pedestrian in front of the vehicle during traveling, the light irradiation device  100  moves an irradiation position in accordance with the pedestrian. 
     The light irradiation device  100  serves as a vehicle lighting device and can be used as a low beam headlight of an automobile or the like. The low beam headlight is a headlight that is used when the vehicle passes by an oncoming vehicle. An illumination distance of the low beam headlight is, for example, 30 m. For example, the light irradiation device  100  moves an irradiation position at high speed to thereby achieve light distribution required for the low beam headlight. 
     The light irradiation device  100  serves as a vehicle lighting device and can be used as a light distribution variable headlight system of an automobile or the like. The light distribution variable headlight system is, for example, an adaptive driving beam (ADB). In order not to dazzle a forward vehicle by a high beam during travelling, the ADB turns off only irradiation on an area that dazzles the front vehicle. The ADB irradiates the other area with the high beam to secure visibility and enhance safety. 
     For such illumination devices, the light irradiation device  100  can reduce blurring of the contour of irradiated light. 
     In the following embodiment, XYZ rectangular coordinates are shown in the figures in order to facilitate description. 
     In the following description, the frontward direction of the light irradiation device  100  will be referred to as a +Z-axis direction, and the rearward direction of the light irradiation device  100  will be referred to as a −Z-axis direction. The front direction of the light irradiation device  100  is a direction in which illumination light is emitted. In the following embodiment, for example, light emitted from a light source  10  is emitted in the +Z-axis direction. The upward direction of the light irradiation device  100  will be referred to as a +Y-axis direction, and the downward direction of the light irradiation device  100  will be referred to as a −Y-axis direction. For example, in the case of a vehicle lighting device, the upward direction of the vehicle is the +Y-axis direction. The downward direction of the vehicle is the −Y-axis direction. As one faces the frontward direction with respect to the light irradiation device  100  (+Z-axis direction), the rightward direction of the light irradiation device  100  will be referred to as a +X-axis direction, and the leftward direction of the light irradiation device  100  will be referred to as a −X-axis direction. The surface side of the figure is the +X-axis direction, and the back side of the figure is the −X-axis direction. 
     First Embodiment 
       FIG. 1  is a view illustrating a configuration of a light irradiation device  100  according to a first embodiment. 
     [Configuration of Light Irradiation Device  100 ] 
     The light irradiation device  100  includes a light source  10 , a projection optical system  20 , a wedge prism  30 , and a wedge prism  40 . The light irradiation device  100  can include rotation mechanisms  50  and  60  and a control circuit  70 . An optical axis C is an optical axis of the light irradiation device  100 . The direction of the optical axis described below can be changed by using a mirror or the like. The positional relationships with respect to the optical axis direction are illustrated while the optical axis is regarded as a straight line. 
     (Light Source  10 ) 
     The light source  10  emits light. The light source  10  emits illumination light. The light source  10  emits light from a light-emitting surface  101 . The light source  10  includes, for example, the light-emitting surface  101  which is planar. That is, the light source  10  is a planar light source. The light source  10  is a light source of planar light emission. The “planar light source” is, for example, a light source that cannot be treated as a point-like light source in a design stage. 
     An optical axis C 10  is an optical axis of the light source  10 . The optical axis C 10  is, for example, an axis passing through the center of the light-emitting surface  101  of the light source  10  and perpendicular to the light-emitting surface  101 . The optical axis C 10  is, for example, a main optical axis of the light source  10 . The main optical axis is not a geometrical center axis of the illumination device but an optical center axis of light emitted from the light source. The main optical axis is generally in an emission direction in which the luminous intensity is maximum. 
     The light source  10  is, for example, an LED. The light source  10  is, for example, a solid light source. In the following description, the light source  10  will be described as an LED. 
     (Projection Optical System  20 ) 
     The projection optical system  20  changes a divergence angle of incident light. The projection optical system  20  makes the divergence angle of emitted light smaller than the divergence angle of incident light. The projection optical system  20  collects light emitted from the light source  10 . In the case where an LED having a large divergence angle is used, the projection optical system  20  can efficiently collect light while the projection optical system  20  is small in size. 
     The projection optical system  20  is, for example, a lens. The projection optical system  20  is, for example, a projection lens. The projection optical system  20  projects a planar image formed based on light emitted from the light source  10 . The projection optical system  20  enlarges and projects the planar image formed based on light emitted from the light source  10 . 
     The projection optical system  20  projects, for example, an image of the light-emitting surface  101  of the light source  10 . For example, the projection optical system  20  projects a light source image. For example, a focal point of the projection optical system  20  is located on the light-emitting surface  101 . The projection optical system  20  converts light emitted from the light source  10  to parallel light, for example. 
     Converting light to parallel light includes converting light emitted from a position on the optical axis C 20  of the light-emitting surface  101  to parallel light and converting light emitted from a periphery of the light-emitting surface  101  to approximate parallel light. The light emitted from the position on the optical axis C 20  of the light-emitting surface  101  is light emitted from a point at intersection of the light-emitting surface  101  with the optical axis C 20 . An optical axis C 20  is an optical axis of the projection optical system  20 . In the following description, the optical axis C 10  and the optical axis C 20  will be described as the same axis. 
     (Wedge Prisms  30  and  40 ) 
     The wedge prism  30  and the wedge prism  20  are held so that at least one of the wedge prism  30  and the wedge prism  40  rotates about a rotation axis A 30  or A 40 . In the following description, however, the wedge prism  30  and the wedge prism  40  are held so that both of the wedge prism  30  and the wedge prism  40  rotate. The wedge prism  30  and the wedge prism  40  deflect incident light. The wedge prism  30  and the wedge prism  40  deflect an incident light beam. 
     The wedge prism  30  receives light emitted from the light source  10 . The wedge prism  30  receives and deflects light emitted from the light source  10 . The wedge prism  30  receives light emitted from, for example, the projection optical system  20 . The wedge prism  30  receives and deflects light emitted from the projection optical system  20 . 
     The wedge prism  30  is held to rotate about the rotation axis A 30 . The rotation axis A 30  is an axis about which the wedge prism  30  rotates. 
     The wedge prism  30  includes an incident surface  301  and an emission surface  302 . 
     The incident surface  301  receives light emitted from the light source  10 . The incident surface  301  receives light emitted from the projection optical system  20 , for example. The incident surface  301  receives light emitted from an emission surface  202  of the projection optical system  20 , for example. 
     The incident surface  301  corrects aberration occurring when an image is projected by the projection optical system  20 . The incident surface  301  corrects aberration occurring on a projected image when the image is projected by the projection optical system  20 . The incident surface  301  corrects aberration occurring when an image of the light-emitting surface  101  is projected by the projection optical system  20 . The incident surface  301  corrects aberration of, for example, a projected light source image. 
     The incident surface  301  is a surface at which aberration is corrected. That is, the incident surface  301  is an aberration correction surface  910 . The aberration correction surface  910  is formed at the incident surface  301  of the wedge prism  30 . 
     The aberration correction surface  910  is, for example, a surface rotationally symmetric with respect to the rotation axis A 30  of the wedge prism  30 . The aberration correction surface  910  formed at the incident surface  301  is, for example, a surface rotationally symmetric with respect to the rotation axis A 30  of the wedge prism  30 . An optical axis C 30  of the aberration correction surface  910  formed at the incident surface  301  and the rotation axis A 30  are the same axis. The aberration correction surface  910  formed at the incident surface  301  is, for example, a surface rotationally symmetric with respect to the optical axis C 30  of the aberration correction surface  910 . 
     The rotation axis A 30  of the wedge prism  30  and the optical axis C 20  of the projection optical system  20  are, for example, the same axis. The optical axis C 10 , the optical axis C 20 , and the rotation axis A 30  are, for example, the same axis. 
     At least in a case where the wedge prism  30  is held to rotate about the rotation axis A 30 , the aberration correction surface  910  is a surface rotationally symmetric with respect to the rotation axis A 30  of the wedge prism  30 . The incident surface  301  has a convex surface shape. The incident surface  301  is, for example, an aspherical surface. The aberration correction surface  910  has a convex surface shape. The aberration correction surface  910  is, for example, an aspherical surface. 
     The emission surface  302  is, for example, a surface tilted relative to a surface perpendicular to the rotation axis A 30 . The emission surface  302  is tilted by a wedge angle α 1 . The wedge angle α 1  is an angle in a case where the incident surface  301  is a surface perpendicular to the rotation axis A 30 . The emission surface  302  is, for example, a flat surface. 
     In the following description, the apex angle will be referred to as a wedge angle α. A wedge angle α of the wedge prism  30  is the wedge angle α 1 . A wedge angle α of the wedge prism  40  described later is a wedge angle α 2 . The wedge angle α 1  of the wedge prism  30  is, for example, equal to the wedge angle α 2  of the wedge prism  40  (α 1 =α 2 ). A material of the wedge prism  30  is, for example, the same as a material of the wedge prism  40 . 
     The wedge prism  30  is provided with a gear  503 . The gear  503  transmits rotational motion from the rotation mechanism  50  to the wedge prism  30 . A driving force from the rotation mechanism  50  is transmitted to the gear  503 . The gear  503  can be provided on a barrel holding the wedge prism  30  or the like. A method for transmitting the driving force from the rotation mechanism  50  to the wedge prism  30  is not limited to the gear  503 . For example, the driving force may be transmitted using a belt or the like. 
     The wedge prism  40  receives light emitted from the wedge prism  30 . The wedge prism  40  receives and deflects light deflected by the wedge prism  30 . 
     The wedge prism  40  is held to rotate about the rotation axis A 40 . The rotation axis A 40  is an axis about which the wedge prism  40  rotates. For example, the rotation axis A 30  and the rotation axis A 40  are the same axis. The optical axis C 10 , the optical axis C 20 , the rotation axis A 30 , and the rotation axis A 40  are, for example, the same axis. 
     The wedge prism  40  includes an incident surface  401  and an emission surface  402 . 
     The incident surface  401  receives light emitted from the wedge prism  30 . The incident surface  401  receives light emitted from the emission surface  302  of the wedge prism  30 . 
     The incident surface  401  is, for example, a surface tilted relative to a surface perpendicular to the rotation axis A 40 . The incident surface  401  is tilted by the wedge angle α 1 . The incident surface  401  is, for example, a flat surface. 
     The emission surface  402  is, for example, a surface perpendicular to the rotation axis A 40 . The emission surface  402  is, for example, a flat surface. 
     The emission surface  402  may be a surface tilted relative to a surface perpendicular to the rotation axis A 40 . The incident surface  401  may be a surface perpendicular to the rotation axis A 40 . 
     The wedge prism  40  is provided with a gear  603 . The gear  603  transmits rotational motion from the rotation mechanism  60  to the wedge prism  40 . A driving force from the rotation mechanism  60  is transmitted to the gear  603 . The gear  603  can be provided on a barrel holding the wedge prism  40  or the like. The method for transmitting the driving force from the rotation mechanism  60  to the wedge prism  40  is not limited to the gear  603 . For example, the driving force may be transferred using a belt or the like. 
     The rotation mechanism  60  is not necessarily needed for driving the wedge prism  40 . For example, the wedge prism  40  may be rotated by transmitting a driving force of the rotation mechanism  50  to the gear  603 . 
     Light emitted from the wedge prism  30  is refracted in accordance with the wedge angle α 1  of the wedge prism  30 . Light emitted from the wedge prism  30  enters the wedge prism  40 . Light emitted from the wedge prism  40  is refracted in accordance with the wedge angle α 2  of the wedge prism  40 . 
     (Rotation Mechanisms  50  and  60 ) 
     The rotation mechanism  50  causes the wedge prism  30  to rotate. The rotation mechanism  50  includes a driving source  501 , a gear  502 , the gear  503 , and a rotation shaft  504 . 
     The driving source  501  is, for example, a motor. The driving source  501  is, for example, a stepping motor or the like. The rotation shaft  504  is a shaft for transmitting rotation of the driving source  501  to the gear  502 . The rotation shaft  504  is, for example, a rotation shaft of the motor. 
     The gear  502  receives a rotational force of the rotation shaft  504  to rotate. The gear  502  rotates by rotation of the rotation shaft  504 . The gear  502  is attached to, for example, the rotation shaft  504 . 
     The gear  502  meshes with the gear  503 . The gear  502  drives the gear  503 . The gear  502  transmits a rotational force to the gear  503 . The gear  502  causes the gear  503  to rotate. 
     The gear  503  rotates about the rotation shaft A 30 . An axis of the gear  503  is the rotation axis A 30 . Rotation of the gear  503  causes the wedge prism  30  to rotate. 
     The gear  503  is formed on, for example, an outer periphery of the wedge prism  30 . The gear  503  is formed on, for example, an outer peripheral portion of the wedge prism  30 . The gear  503  is formed on, for example, a member holding the wedge prism  30 . The member holding the wedge prism  30  is, for example, a barrel, a prism frame or the like. The gear  503  is formed on, for example, the barrel holding the wedge prism  30 . 
     The rotation mechanism  60  causes the wedge prism  40  to rotate. The rotation mechanism  60  includes a driving source  601 , a gear  602 , the gear  603 , and a rotation shaft  604 . 
     The driving source  601  is, for example, a motor. The driving source  601  is, for example, a stepping motor or the like. The rotation shaft  604  is a shaft for transmitting rotation of the driving source  601  to the gear  602 . The rotation shaft  604  is, for example, a rotation shaft of the motor. 
     The gear  602  receives a rotational force of the rotation shaft  604  to rotate. The gear  602  rotates by rotation of the rotation shaft  604 . The gear  602  is attached to, for example, the rotation shaft  604 . 
     The gear  602  meshes with the gear  603 . The gear  602  drives the gear  603 . The gear  602  transmits a rotational force to the gear  603 . The gear  602  causes the gear  603  to rotate. 
     The gear  603  rotates about the rotation axis A 40 . An axis of the gear  603  is the rotation axis A 40 . Rotation of the gear  603  causes the wedge prism  40  to rotate. 
     The gear  603  is formed on, for example, an outer periphery of the wedge prism  40 . The gear  603  is formed on, for example, an outer peripheral portion of the wedge prism  40 . The gear  603  is formed on, for example, a member holding the wedge prism  40 . The member holding the wedge prism  40  is, for example, a barrel, a prism frame or the like. The gear  603  is formed on, for example, a barrel holding the wedge prism  40 . 
     (Control Circuit  70 ) 
     The control circuit  70  controls, for example, rotation amount or rotation speed of the rotation mechanism  50 . The control circuit  70  controls, for example, rotation amount or rotation speed of the rotation mechanism  60 . The rotation mechanism  60  and the control circuit  70  may be controlled by different control circuits. 
     [Aberration Correction by Light Irradiation Device  100 ] 
     The incident surface  301  has the aberration correction surface  910 . The incident surface  301  is, for example, the aberration correction surface  910 . Aberrations corrected by the incident surface  301  are, for example, commonly known five Seidel aberrations. Specifically, aberrations corrected by the incident surface  301  are spherical aberration, coma aberration, field curvature aberration, astigmatism aberration, and distortion aberration. 
     The incident surface  301  is effective for correcting these aberrations. The incident surface  301  reduces blurring of the contour of an image irradiated onto the irradiation surface. The incident surface  301  corrects blurring of the contour of an image on the irradiation surface. With the incident surface  301 , an image whose shape deformation is reduced is projected. 
     An image projected by the light irradiation device  100  includes a light distribution pattern. An image projected by the projection optical system  20  includes a light distribution pattern. The light distribution pattern includes the shape of light distribution and light distribution. The light distribution indicates how intensely light is emitted in each direction (angle) from a light source. The light distribution is a change or a distribution of luminous intensity of the light source or an illumination device with respect to an angle. 
     The incident surface  301  corrects deformation of a light distribution pattern projected on the irradiation surface. The light distribution pattern is formed based on light emitted from the light source  10 . The light distribution pattern is formed based on, for example, a light source image. The image projected by the projection optical system  20  is, for example, an image of the light source  10 . The image projected by the projection optical system  20  is, for example, a light distribution pattern. 
     The incident surface  301  of the wedge prism  30  has a positive refractive power. The aberration correction surface  910  formed at the incident surface  301  of the wedge prism  30  has a positive refractive power. The projection optical system  20  has a positive refractive power. The refractive power of the incident surface  301  of the wedge prism  30  is smaller than the refractive power of the projection optical system  20 , for example. 
     It is conceivable to form the aberration correction surface  910  at the incident surface  201  or the emission surface  202  of the projection optical system  20 . However, the diameter of a light beam passing through the projection optical system  20  is smaller than the diameter of the light beam incident on the wedge prism  30 . This is because the light-emitting surface  101  of the light source  10  has an area. 
     As above, the light source  10  is described as, for example, an LED. That is, light emitted from the center of the light-emitting surface  101  of the light source  10  is light parallel to the optical axis C 20  of the projection optical system  20 . In contrast, light emitted from a peripheral portion of the light-emitting surface  101  of the light source  10  is tilted relative to the optical axis C 20 . Thus, light emitted from the projection optical system  20  is not completely parallel to the optical axis C 20 . Light emitted from the projection optical system  20  is expanded light. The “light changed to parallel light” includes light tilted relative to an optical axis of an optical system for converting light to parallel light. In this example, the optical system for converting light to parallel light is the projection optical system  20 . 
     Thus, the diameter of the light beam passing through the projection optical system  20  is smaller than the diameter of the light beam incident on the wedge prism  30 . The greatest advantage is obtained when aberration correction is performed at a position where the beam diameter is the largest. For this reason, it is advantageous that the incident surface  201  or the emission surface  202  of the projection optical system is not the aberration correction surface  910  but the incident surface  301  of the wedge prism  30  is the aberration correction surface  910 . 
     The emission surface  302  of the wedge prism  30  reflects light passing through the emission surface  302 , in one direction. That is, the emission surface  302  deflects light passing through the emission surface  302 , in one direction. Accordingly, light passing through the emission surface  302  of the wedge prism  30  does not show an isotropic distribution with respect to the optical axis C 20  of the projection optical system  20 . 
     Thus, even if aberration correction is performed for light passing through the emission surface  302  of the wedge prism  30 , the effect of aberration correction is reduced. It is more advantageous for aberration correction to form the aberration correction surface  910  at the incident surface  301  of the wedge prism  30  than to form the aberration correction surface  910  at any one of the emission surface  302 , the incident surface  401 , and the emission surface  402 . 
       FIG. 2  is a view illustrating light-collecting spots in a case where light-emitting points S n  on the light-emitting surface  101  are projected.  FIG. 2  shows light-collecting spots in a case where emitted light is deflected in the −X-axis direction by the light irradiation device  100 .  FIG. 2  is a view showing a spot diagram. The “spot diagram” is a diagram obtained by tracking a number of light rays from the light source to an image plane and plotting locations on the image plane where the light rays reach. The spot diagram is suitable for visually recognizing the degree of light collection or a geometric behavior of aberration. 
     The two wedge prisms  30  and  40  are rotated by 45 degrees in opposite directions with respect to a reference position. The reference position for the wedge prisms  30  and  40  is a position at which the emission surface  302  is parallel to a tilt surface of the wedge prism  40 . 
     In  FIG. 1 , the tilt surface of the wedge prism  40  is the incident surface  401 . That is, in  FIG. 1 , the reference position is a position in which the emission surface  302  and the incident surface  401  are parallel to each other.  FIG. 1  shows a state where the wedge prisms  30  and  40  are in the reference position. In the reference position illustrated in  FIG. 1 , a thinnest portion of the wedge prism  30  is located on the +Y-axis direction side. A thinnest portion of the wedge prism  40  is located on the −Y-axis direction side. 
       FIG. 3  is a view illustrating light-emitting points S n  on the light-emitting surface  101 . Light-collecting spots P n  illustrated in  FIG. 2  are light-collecting spots on the irradiation surface formed by light emitted from light-emitting points S n  on the light-emitting surface  101  illustrated in  FIG. 3 . The light-emitting point S 1  is located at the center of the light-emitting surface  101 . The light-emitting point S 1  is located on the optical axis C 10  of the light source  10 , for example. The light-emitting points S 2 , S 3 , S 4 , and S 5  are located at four corners of the light-emitting surface  101 . The light-emitting points S 6 , S 7 , S 8 , and S 9  are located at respective intermediate points of the four sides of the light-emitting surface  101 .  FIG. 3  is a view as seen from the backside (from the −Z-axis direction) of the light-emitting surface  101 . 
     When n represents an integer from 1 to 9, the light-collecting spots P n  illustrated in  FIG. 2  are light-collecting spots of light emitted from the light-emitting points S n  illustrated in  FIG. 3 . Light emitted from the point S n  is collected at a position opposite to the point S n  in the X-axis direction with respect to the optical axis C 20  of the projection optical system  20 . Light emitted from the point S n  is collected at a position opposite to the point S n  in the Y-axis direction with respect to the optical axis C 20 . The optical axis C 10  of the light source  10  and the optical axis C 20  of the projection optical system  20  are the same axis. 
     Comparative Example 
       FIG. 4  is a view schematically illustrating a configuration of a light irradiation device  200 . The light irradiation device  200  illustrated in  FIG. 4  is a comparative example. The light irradiation device  200  is different from the light irradiation device  100  in that the light irradiation device  200  uses a wedge prism  80  instead of the wedge prism  30 . Except for the use of the wedge prism  80 , the light irradiation device  200  is similar to the light irradiation device  100 . Components which are similar to those of the light irradiation device  100  are denoted by the same reference characters, and description thereof will be omitted. 
     The wedge prism  80  is held to rotate about a rotation axis A 80 . 
     An incident surface  801  of the wedge prism  80  is a flat surface. The incident surface  801  is a surface perpendicular to the rotation axis A 80 . That is, the light irradiation device  200  does not has a surface for correcting an aberration. The light irradiation device  200  does not have the aberration correction surface  910 . 
       FIG. 5  is a view illustrating a spot diagram of the light irradiation device  200 .  FIG. 5  shows light-collecting spots in a case where emitted light is deflected in the −X-axis direction by the light irradiation device  200 . The two wedge prisms  80  and  40  are rotated by 45 degrees in opposite directions with respect to a reference position. 
     The diameters of light-collecting spots of the light irradiation device  200  are larger than the diameters of light-collecting spots of the light irradiation device  100 . That is, large aberrations occur on an irradiation surface in the light irradiation device  200 . Thus, the contour of irradiation light is blurred. 
     That is, by forming the aberration correction surface  910  at the incident surface  301  of the wedge prism  30 , occurrence of aberrations on the irradiation surface can be reduced. That is, blurring of the contour of irradiation light is reduced. 
     [Modification] 
       FIG. 6  is a view illustrating a configuration of a light irradiation device  300  according to a modification. 
     The light irradiation device  300  is different from the light irradiation device  100  in that the light irradiation device  300  includes a wedge prism  80  instead of the wedge prism  30  and includes an aberration correcting optical system  90 . The light irradiation device  300  is different from the light irradiation device  200  in that the light irradiation device  300  includes the aberration correcting optical system  90 . The other structures of the light irradiation device  300  are similar to those of the light irradiation devices  100  and  200 . Components which are similar to those of the light irradiation devices  100  and  200  are denoted by the same reference characters, and description thereof will be omitted. 
     The aberration correcting optical system  90  is disposed between the projection optical system  20  and the wedge prism  80 . The aberration correcting optical system  90  includes the aberration correction surface  910 . The aberration correction surface  910  is formed in the aberration correcting optical system  90 . The aberration correcting optical system  90  includes the aberration correction surface  910 . 
     The aberration correcting optical system  90  is, for example, a lens. The aberration correcting optical system  90  may be, for example, one lens. Alternatively, the aberration correcting optical system  90  may include, for example, a plurality of lenses. 
     In  FIG. 6 , the aberration correction surface  910  is formed at, for example, an incident surface  901  of the aberration correcting optical system  90 . For example, the aberration correction surface  910  is included in the incident surface  901  of the aberration correcting optical system  90 . Alternatively, the aberration correction surface  910  may be formed at the emission surface  902  of the aberration correcting optical system  90 . The aberration correction surface  910  may be included in the emission surface  902  of the aberration correcting optical system  90 . The aberration correction surface  910  may be formed at a plurality of surfaces of the aberration correcting optical system  90 . The aberration correction surface  910  may be included in a plurality of surfaces of the aberration correcting optical system  90 . 
     An optical axis C 90  is an optical axis of the aberration correcting optical system  90 . The optical axis C 90  and the optical axis C 20  are, for example, the same axis. The optical axis C 10 , the optical axis C 20 , the optical axis C 90 , the rotation axis A 80 , and the rotation axis A 40  are, for example, the same axis. 
     The aberration correction surface  910  of the light irradiation device  100  is provided on the incident surface  301  of the wedge prism  30 . The aberration correction surface  910  of the light irradiation device  300  is located on the wedge prism  30  side with respect to the emission surface  202  of the projection optical system  20 . That is, the aberration correction surface  910  is located on the wedge prism  30  side with respect to the emission surface  202  of the projection optical system  20 . With respect to the wedge prism  30 , the aberration correction surface  910  is located on the projection optical system  20  side including the incident surface  301  of the wedge prism  30 . 
     In the foregoing embodiment, terms such as “parallel”, “perpendicular” indicating positional relationships among components, and terms indicating the shapes of the components are used. These terms include a range in which manufacturing tolerance and assembly variation are taken into consideration. 
     Although the embodiment of the present invention has been described, the invention is not limited to the embodiment. 
     DESCRIPTION OF REFERENCE CHARACTERS 
       100 ,  200 ,  300  light irradiation device;  10  light source;  101  light-emitting surface;  20  projection optical system;  30 ,  40 ,  80  wedge prism;  301 ,  401 ,  801  incident surface;  302 ,  402 ,  802  emission surface;  50 ,  60  rotation mechanism;  501 ,  601  driving source;  502 ,  503 ,  602 ,  603  gear;  504 ,  604  rotation shaft;  70  control circuit;  90  aberration correcting optical system;  901  incident surface;  902  emission surface;  910  aberration correction surface; A 30 , A 40 , A 80  rotation axis; C, C 10 , C 20 , C 30 , C 90  optical axis; P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , P 8 , P 9  light-collecting spot; S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , S 9  light-emitting point; α, α 1 , α 2  wedge angle.