JP2017102391A - Illumination apparatus, image projector and illumination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination apparatus, an image projector and an illumination method capable of preventing a diffusion plate from getting damaged.SOLUTION: An illumination apparatus 100 includes: a coherent light source system 101 that emits coherent light; a condenser lens 102 that condenses the coherent light; an integrator 104 that equalizes in-plane light intensity distribution of the condensed coherent light; and a diffusion plate 103 which is disposed being inclined with respect to the center optical axis of the coherent light between the condenser lens 102 and the integrator 104.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an illumination device, an image projection device, and an illumination method, and more particularly to an illumination device, an image projection device, and an illumination method using a laser light source.

  As one of image display methods, a projection display method is used in which modulated light source light is projected onto a screen to display an image. The lamp light source used in this projection display system has problems such as short life, limited color reproduction region, and low light utilization efficiency.

  In order to solve this problem, attempts have been made in recent years to use a laser light source as a light source for a projection display. Since the laser light source has a longer life and stronger directivity than the lamp light source, it is easy to improve the light utilization efficiency. In addition, since the laser light emitted from the laser light source is excellent in monochromaticity, a region where the color can be reproduced can be expanded from the lamp light source, and a colorful image display becomes possible.

  On the other hand, in image display using a laser light source, there is a problem of speckle noise in which the laser beams interfere with each other and the reflected light on the screen is shaded. There is a possibility that the viewer recognizes minute uneven speckle noise generated in the image displayed on the screen, and the speckle noise may cause discomfort.

  In order to reduce the speckle noise, devices described in Patent Documents 1 and 2 have been proposed. Patent Document 1 describes an exposure illumination device in which a rotating diffusion plate is disposed in an optical system, and coherent light is converted into incoherent light by the diffusion plate. Patent Document 2 describes a projection display device in which a diffusing plate that moves (rotates and / or vibrates) is disposed in an optical system, and coherent light is converted into incoherent light by the diffusing plate.

JP 7-297111 A JP-A-6-208086

  However, in the devices described in Patent Documents 1 and 2, since the light from the light source is collected and applied to the diffusion plate, the density of the light applied to the diffusion plate is high, and the diffusion plate is damaged by heating or the like. was there.

  An object of this invention is to provide the illuminating device, the image projector, and the illuminating method which can suppress the damage of a diffuser plate.

  The illumination device of the present invention includes a coherent light source system that emits coherent light, a condensing lens that condenses the coherent light, an integrator that receives the collected coherent light, and a space between the condensing lens and the integrator. And a diffuser plate arranged to be inclined with respect to the central optical axis of the coherent light.

  The image projection device of the present invention is an image projection device comprising at least one illumination device and a projection device that projects an image using light emitted from the illumination device, wherein the illumination device comprises coherent light. A coherent light source system that emits light, a condensing lens that condenses the coherent light, an integrator that receives the collected coherent light, and a central optical axis of the coherent light between the condensing lens and the integrator. And a diffusing plate arranged to be inclined with respect to.

  In the illumination method of the present invention, a diffusing plate is inclined with respect to the central optical axis of the collected coherent light, the coherent light transmitted through the diffusing plate is incident on an integrator, and light is emitted from the integrator. It was made to emit.

  According to the illumination device, the image projection device, and the illumination method of the present invention, it is possible to suppress damage to the diffusion plate.

1 is a schematic diagram illustrating a configuration of an optical system of an illumination apparatus according to a first embodiment. It is the schematic which shows the structure of the optical system of the illuminating device of a reference example. 3 is a graph showing a peak distribution of light irradiated on the diffusion plate of the lighting apparatus according to the first embodiment. It is a graph which shows the peak distribution of the light irradiated to the diffusion plate of the illuminating device of a reference example. It is the schematic explaining the difference between the diffusion plate of Embodiment 1, and the diffusion plate of a reference example. FIG. 3 is a photograph taken of light irradiated on the diffusion plate of the lighting apparatus according to the first embodiment. FIG. It is the photograph which image | photographed the light irradiated to the diffusion plate of the illuminating device of a reference example. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser, and the peak intensity of the light which injects into a diffuser. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser, and the peak intensity of the light which injects into a diffuser. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser, and the peak intensity of the light which injects into a diffuser. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser, and the peak intensity of the light which injects into a diffuser. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser, and the peak intensity of the light which injects into a diffuser. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser plate, and the power of the light in an integrator output surface. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser plate, and the power of the light in an integrator output surface. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser plate, and the power of the light in an integrator output surface. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser plate, and the power of the light in an integrator output surface. It is a graph which shows the relationship between the arrangement | positioning angle of a diffuser plate, and the power of the light in an integrator output surface. FIG. 4 is a schematic diagram illustrating a configuration of an optical system of an illumination apparatus according to a second embodiment. FIG. 6 is a schematic diagram illustrating a configuration of an optical system of an image projection apparatus according to a third embodiment.

(Embodiment 1)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of an optical system of the illumination apparatus according to the first embodiment. In FIG. 1, the illumination device 100 includes a coherent light source system 101, a condenser lens 102, a diffusion plate 103, and an integrator 104. The coherent light source system 101 includes coherent light sources 111-1 to 111-n (n is an arbitrary natural number) and collimating lenses 112-1 to 112-n.

  The coherent light sources 111-1 to 111-n are light sources that emit coherent light. For example, the coherent light source 111 is configured by a laser diode. The coherent light sources 111-1 to 111-n are arranged in a plurality of rows and columns.

  The collimating lenses 112-1 to 112-n refract the coherent light emitted from the coherent light source 111 into parallel light. Similar to the coherent light sources 111-1 to 111-n, the collimating lenses 112-1 to 112-n are arranged in a plurality of rows and columns. That is, the collimating lenses 112-1 to 112-n are respectively arranged on the optical axes of the coherent light sources 111-1 to 111-n.

  The coherent light source system 101 includes the above-described coherent light sources 111-1 to 111-n and collimating lenses 112-1 to 112-n, and emits parallel coherent light.

  The condenser lens 102 is disposed on the optical axis of the coherent light source system 101. The condensing lens 102 condenses the coherent light that has been converted into parallel light by the collimating lens 112. For example, the condensing lens 102 is a convex lens.

  The diffusion plate 103 is disposed between the condenser lens 102 described above and an integrator 104 described later. The diffuser plate 103 randomly scatters the coherent light collected by the condenser lens 102, averages the spatial / temporal light intensity, phase, and polarization direction of the coherent light, and makes the incident light The coherent light is converted into incoherent light (pseudo thermal radiation light).

  For example, the diffusion plate 103 is configured to diffuse light refracted from the condenser lens 102 at a predetermined diffusion angle. Specifically, the diffusing plate 103 is a polished glass, a holographic diffuser, a surface of a transparent substrate that is blasted to form irregularities, and a scattering material such as beads is dispersed inside the transparent substrate. A material that scatters light by means of is preferable. Further, the diffusing plate 103 is rotated or vibrated by a driving element, thereby making scattering irregularly and converting incident coherent light into incoherent light.

  The diffusion plate 103 is arranged to be inclined with respect to the central optical axis of the coherent light. In other words, the angle formed by the diffusion plate 103 and the central optical axis of the coherent light is an angle greater than 0 ° and less than 90 °. Further, the angle formed by the diffuser plate 103 and the central optical axis of the coherent light includes an angle larger than −90 ° and smaller than 0 °. That is, the positive angle and the negative angle are symmetric with respect to the central optical axis, meaning the same angle. In other words, the absolute values are the same.

  In addition, since the diffusion plate is disposed at a high-density location where light is condensed, it is generally preferable that the diffusion plate is made of a glass material having high heat resistance.

  The integrator 104 makes the luminance distribution of the luminous flux uniform with respect to the incident light. For example, the integrator 104 is configured by a hollow body having a cylinder, a polygonal column, or a side surface of a polygonal pyramid. The integrator 104 is preferably configured by a light tunnel that configures the inner side surface with a reflection mirror so that incident light is reflected a plurality of times on the inner side surface and uniformizes the luminance distribution. Further, the integrator 104 may be configured by a glass rod, a rod integrator, or a rod lens that creates a polygonal column with a transparent material such as glass and uses total reflection on the side surface.

  As described above, as shown in FIG. 1, the condenser lens 102, the diffusion plate 103, and the integrator 104 are arranged on the central optical axis of the coherent light, and the diffusion plate 103 is arranged to be inclined with respect to the central optical axis. The

  The point where the diffusing plate 103 is arranged to be inclined with respect to the central optical axis will be described in comparison with an example of a diffusing plate arranged perpendicular to the central optical axis. FIG. 2 is a schematic diagram showing the configuration of the optical system of the illumination device of the reference example. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 2, the diffusing plate 201 is disposed perpendicular to the central optical axis of coherent light.

  The light irradiated on the diffusion plate 103 in FIG. 1 and the diffusion plate 201 in FIG. 2 will be compared below. FIG. 3 is a graph showing a peak distribution of light irradiated on the diffusion plate of the lighting apparatus according to the first embodiment. FIG. 4 is a graph showing the peak distribution of light irradiated on the diffusion plate of the illumination device of the reference example. 3 and 4, the horizontal axis indicates the position on the X-axis (that is, the position in the vertical direction of the diffuser plate in FIGS. 1 and 2), and the vertical axis indicates the amount of light incident on the diffuser plate. .

  As shown in FIGS. 3 and 4, a peak appears at a position on the X axis where the light emitted from the plurality of coherent light sources 111-1 to 111-n interferes with each other and emphasizes each other. When FIG. 3 and FIG. 4 are compared, the incident amount of light is higher in the reference example than in the first embodiment. In other words, the diffusion plate of Embodiment 1 is less likely to break because the density of incident light is lower than that of the reference example.

  The difference in the density of the incident light will be described with reference to FIG. FIG. 5 is a schematic diagram illustrating the difference between the diffusion plate of Embodiment 1 and the diffusion plate of the reference example. As shown in FIG. 5, when the diffusing plate 201 is arranged perpendicularly to the central optical axis as in the reference example, light enters the narrow area S1, but the central optical axis as in the first embodiment. If the diffusing plate 103 is disposed with an inclination with respect to the light, light enters a wider area S2. On the other hand, since the amount of incident light is the same, the diffuser plate of Embodiment 1 has a lower incident light density per unit area than the reference example (that is, the light density is lower). ).

  An example in which an area where light is actually incident is observed will be described with reference to FIGS. FIG. 6 is a photograph of the light irradiated on the diffusion plate of the lighting apparatus according to the first embodiment. FIG. 7 is a photograph of the light irradiated on the diffusion plate of the illumination device of the reference example. When FIG. 6 is compared with FIG. 7, the interference fringes are longer in the diffusing plate of the first embodiment shown in FIG. Therefore, it can be said that the diffusion plate of Embodiment 1 has a light incident area larger than that of the reference example.

  As described above, according to the irradiation apparatus of the first embodiment, by arranging the diffusing plate to be inclined with respect to the central optical axis of the coherent light, the density of the incident light is reduced, and the diffusing plate is prevented from being damaged. be able to.

  Next, the angle at which the diffusion plate is arranged will be described in more detail. As described above, the peak intensity of light incident on the diffusion plate is related to the arrangement angle of the diffusion plate with respect to the central optical axis of the coherent light. Further, since the coherent light refracted in the condenser lens 102 converges toward the integrator 104 and the light density increases, the peak intensity of the light incident on the diffusion plate is also related to the distance between the diffusion plate and the integrator.

  Therefore, the range in which the peak intensity of the light incident on the diffusion plate is appropriate is examined for both the arrangement angle of the diffusion plate and the distance between the diffusion plate and the integrator. 8 to 12 are graphs showing the relationship between the arrangement angle of the diffusion plate and the peak intensity of light incident on the diffusion plate. 8 to 12, the horizontal axis indicates the arrangement angle of the diffusion plate with respect to the central axis of coherent light, and the vertical axis indicates the peak intensity of light incident on the diffusion plate.

  8 to 12 are different from each other in the distance L (see FIG. 1) between the diffusion plate and the integrator. FIG. 8 shows an example in which the distance L between the diffusion plate and the integrator is 20 mm. FIG. 9 shows an example in which the distance L between the diffusion plate and the integrator is 22 mm. FIG. 10 shows an example in which the distance L between the diffusion plate and the integrator is 24 mm. FIG. 11 shows an example in which the distance L between the diffusion plate and the integrator is 26 mm. FIG. 12 shows an example in which the distance L between the diffusion plate and the integrator is 28 mm.

  As shown in FIGS. 8 and 9, when the arrangement angle of the diffusion plate is larger than 60 ° (or smaller than −60 °), the peak intensity of the incident light is indicated by the shaded state of the diffusion plate. It becomes the peak intensity that causes fear. FIG. 10 shows that the distance between the diffuser and the integrator is longer than in FIGS. 8 and 9, but similarly, when the arrangement angle of the diffuser is larger than 65 °, the peak intensity of the incident light is shown by the shaded plate. The peak intensity at which damage may occur. Further, in FIGS. 11 and 12, where the distance between the diffuser plate and the integrator is long, when the arrangement angle of the diffuser plate is larger than 70 ° or 75 °, the peak intensity of the incident light is broken in the diffuser plate, which is indicated by shading. This is the peak intensity at which there is a risk of this. Therefore, if the arrangement angle of the diffusion plate is 60 ° or less, the peak intensity of light is considered to be in a range where there is no risk of damage to the diffusion plate regardless of the distance between the diffusion plate and the integrator.

  Thus, according to the irradiation apparatus of Embodiment 1, the absolute value of the angle formed by the diffusion plate with respect to the central optical axis of the coherent light is set to 60 degrees or less, so that the incident light density can be more sufficiently achieved. And the breakage of the diffusion plate can be more sufficiently suppressed.

  On the other hand, the distance between the diffusion plate and the integrator is also related to the intensity of light emitted from the integrator. 13 to 17 are graphs showing the relationship between the arrangement angle of the diffusing plate and the light power on the integrator exit surface. 13 to 17, the horizontal axis indicates the arrangement angle of the diffusion plate with respect to the central axis of the coherent light, and the vertical axis indicates the intensity (total power) of the light emitted from the integrator.

  Similar to FIGS. 8-12, FIGS. 13-17 differ from each other in the distance L between the diffuser and the integrator. FIG. 13 shows an example in which the distance L between the diffusion plate and the integrator is 20 mm. FIG. 14 shows an example in which the distance L between the diffusion plate and the integrator is 22 mm. FIG. 15 shows an example in which the distance L between the diffusion plate and the integrator is 24 mm. FIG. 16 shows an example in which the distance L between the diffusion plate and the integrator is 26 mm. FIG. 17 shows an example in which the distance L between the diffusion plate and the integrator is 28 mm.

  As shown in FIGS. 13-16, the intensity | strength of the light radiate | emitted from an integrator is maintaining predetermined intensity | strength. However, as shown in FIG. 17, in the example in which the distance between the diffusion plate and the integrator is 28 mm, if the arrangement angle of the diffusion plate is smaller than 30 °, the light loss is reduced as shown by the shaded area. Large light intensity is insufficient.

  Therefore, if the arrangement angle of the diffusion plate is 30 ° or more (−30 ° or less), the loss of light is small, and the intensity of the light emitted from the integrator is sufficient.

  As described above, according to the irradiation apparatus of the first embodiment, the absolute value of the angle formed by the diffusion plate with respect to the central optical axis of the coherent light is set to 30 degrees or more, thereby irradiating light with sufficient light intensity. can do.

(Embodiment 2)
In the second embodiment, an example in which white light is obtained using a light source having a plurality of wavelengths will be described. Specifically, in the second embodiment, green light is obtained by exciting a phosphor with blue laser light, and red light and blue light are obtained using a red laser and a blue laser as light sources, and green light and red light are obtained. A lighting device that combines white light and obtains white light will be described. FIG. 18 is a schematic diagram illustrating a configuration of an optical system of the illumination apparatus according to the second embodiment. 18, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 18, the illumination device 300 includes a coherent light source system 101, a condenser lens 102, a diffuser plate 103, an integrator 104, a lens 301, a blue reflection-green transmission dichroic mirror 302, a lens 303, and a lens 304. A lens 305, a phosphor 306, a lens 307, red laser diodes 308-1 to 308-n, lenses 309-1 to 309-n, a lens 310, a diffuser plate 311, a lens 312, Red reflection-green transmission dichroic mirror 313, blue laser diodes 314-1 to 314-n, lenses 315-1 to 315-n, lens 316, diffuser 317, lens 318, blue reflection-green red A transmissive dichroic mirror 319, a lens 320, and an integrator 321 are provided. That.

  The diffusing plate 311 and the diffusing plate 317 may be disposed so as to be inclined with respect to the central optical axis, like the diffusing plate 103.

  First, an optical system for obtaining green light by irradiating a phosphor by applying the irradiation apparatus of Embodiment 1 to blue laser light will be described.

  The blue laser light emitted from the integrator 104 passes through the lens 301, is reflected by the blue reflection-green transmission dichroic mirror 302, passes through the lenses 303, 304, and 305, and is irradiated on the phosphor 306. The phosphor 306 is excited by blue laser light and emits green light.

  Green light emitted from the phosphor 306 passes through the lenses 305, 304, and 303, passes through the blue reflection-green transmission dichroic mirror 302, the lens 307, the red reflection-green transmission dichroic mirror 313, and transmits blue reflection-green red. The light is reflected by the dichroic mirror 319, passes through the lens 320, and enters the integrator 321.

  Next, an optical system for red light and blue light will be described. In the second embodiment, red light is diffused with red laser light for red light. Similarly, blue light is made into a blue light source by diffusing blue laser light. These laser beams are emitted from a light emitting point having a very small area using a laser diode. And the light radiated | emitted from the laser diode is made into parallel light by a collimating lens. The parallel light is a light beam that has a very small light spread and high straightness. The light from the green phosphor described above is diffused light and has a large spread of light. Thus, red light, blue light and green light have different radiation angle characteristics.

  Red light is emitted from red laser diodes 308-1 to 308-n arranged on a plane. The red light is collimated by the lenses 309-1 to 309-n. Further, the red light is collected by the lens 310. After being condensed, the red light is diffused by the diffusion plate 311. The diffused red light passes through the lens 312, is reflected by the red reflection-green transmission dichroic mirror 313 and the blue reflection-green-red transmission dichroic mirror 319, passes through the lens 320, and enters the integrator 321.

  Similarly, blue light is emitted from blue laser diodes 314-1 to 314-n arranged on a plane. Then, the blue light is collimated by the lenses 315-1 to 315-n. Further, the blue light is collected by the lens 316. After being collected, the blue light is diffused by the diffusion plate 317. The diffused blue light passes through the lens 318 and the blue reflection-green-red transmission dichroic mirror 319 and enters the integrator 321.

  Then, white light is obtained by combining the green light, red light, and blue light obtained by each optical system using a red reflection-green transmission dichroic mirror 313 and a blue reflection-green-red transmission dichroic mirror 319.

  Thus, according to the irradiation apparatus of the second embodiment, in the optical system that synthesizes light of a plurality of wavelengths, the diffusing plate is disposed so as to be inclined with respect to the central optical axis of the coherent light. The density is reduced, and breakage of the diffusion plate can be suppressed.

(Embodiment 3)
In the third embodiment, an example in which the illumination device of the first and second embodiments is applied to an image projection device will be described. FIG. 19 is a schematic diagram illustrating a configuration of an optical system of the image projection apparatus according to the third embodiment. 19, the same components as those in FIG. 1 or FIG. 18 are denoted by the same reference numerals and description thereof is omitted.

  In FIG. 19, an image projection apparatus 400 includes a coherent light source system 101, a condenser lens 102, a diffuser plate 103, an integrator 104, a lens 301, a blue reflection-green transmission dichroic mirror 302, a lens 303, and a lens. 304, a lens 305, a phosphor 306, a lens 307, red laser diodes 308-1 to 308-n, lenses 309-1 to 309-n, a lens 310, a diffuser plate 311, and a lens 312. , Red reflection-green transmission dichroic mirror 313, blue laser diodes 314-1 to 314-n, lenses 315-1 to 315-n, lens 316, diffusion plate 317, lens 318, and blue reflection-green A red transmissive dichroic mirror 319, a lens 320, an integrator 321, It includes a lens 401, a lens 402, a mirror 403, a lens 404, a TIR prism 405, a color prism 406, and green DMD (Digital Mirror Device) 407, and a projection lens 408, a.

  The light emitted from the integrator 321 is white light obtained by adding yellow light obtained by combining green light and red light and blue light.

  The white light emitted from the integrator 321 passes through the lenses 401 and 402, is reflected by the mirror 403, passes through the lens 404, and enters the TIR prism 405.

  The light incident on the TIR prism 405 is reflected inside the prism and is incident on the color prism 406. The color prism 406 is a prism that separates white light into green, red, and blue.

  In FIG. 19, only the green light path is shown due to the constraints represented by the plane. Similarly, the red and blue light paths also exist three-dimensionally. That is, in the image projection apparatus 400, a red DMD and a blue DMD (not shown) are arranged in parallel with the green DMD 407.

  The green light dispersed by the color prism 406 enters the green DMD 407. The green light is modulated in the DMD 407 for green according to the image to be projected, reflected by changing the ray angle, and is incident on the color prism 406 again.

  Similarly, red light and blue light separated by the color prism 406 are respectively incident on a red DMD and a blue DMD (not shown), modulated by the red DMD and the blue DMD, and reflected by changing the light beam angle. Then, it enters the color prism again. Green light, red light, and blue light incident on the color prism 406 are combined by the color prism 406 and incident on the TIR prism 405.

  The combined light passes through the TIR prism 405, enters the projection lens 408, and is projected onto the screen.

  As described above, according to the image projection apparatus of the third embodiment, by arranging the diffusing plate to be inclined with respect to the central optical axis of the coherent light, the density of the incident light is lowered and the diffusing plate is prevented from being damaged. can do.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the third embodiment describes an example applied to a three-plate DMD projector optical system, but an optical system other than the three-plate DMD projector optical system may also be used. The axis for inclining the diffusion plate may be any as long as it has a predetermined angle with respect to the central optical axis.

  Moreover, although the said embodiment demonstrated the example provided with three light source systems, the number of light source systems is not specifically limited. In the above embodiment, an example in which a diffuser plate is arranged for one light source system is described. However, with respect to a plurality of light source systems, the diffuser plate is inclined with respect to the central optical axis. May be arranged.

100, 300 Illumination device 101 Coherent light source system 102 Condensing lens 103, 201, 311, 317 Diffuser plate 104, 321 Integrator 111-1 to 111-n Coherent light source 112-1 to 112-n Collimating lens 301, 303, 304, 305, 307, 309, 310, 312, 315, 316, 318, 320, 401, 402, 404 Lens 302 Blue reflection-green transmission dichroic mirror 306 Phosphor 308 Red laser diode 313 Red reflection-green transmission dichroic mirror 314 Blue laser Diode 319 Blue reflection-green red transmission dichroic mirror 400 Image projection device 403 Mirror 405 Prism 406 Color prism 407 Green DMD
408 Projection lens

Claims (6)

A coherent light source system that emits coherent light;
A condenser lens for condensing the coherent light;
An integrator on which the collected coherent light is incident;
An illuminating device comprising: a diffusing plate disposed between the condenser lens and the integrator so as to be inclined with respect to a central optical axis of the coherent light.   The lighting device according to claim 1, wherein an absolute value of an angle formed by the diffuser plate and a central optical axis is 60 degrees or less.   The lighting device according to claim 1 or 2, wherein an absolute value of an angle formed by the diffuser plate and a central optical axis is 30 degrees or more.   The illuminating device according to any one of claims 1 to 3, wherein a distance between the diffuser plate and the integrator in a central optical axis is 22 mm or more and 26 mm or less. At least one lighting device;
A projection device that projects an image using light emitted from the illumination device, and an image projection device comprising:
The lighting device includes:
A coherent light source system that emits coherent light;
A condenser lens for condensing the coherent light;
An integrator on which the collected coherent light is incident;
An image projection apparatus comprising: a diffusion plate disposed between the condenser lens and the integrator so as to be inclined with respect to a central optical axis of the coherent light.   An illuminating method in which a diffuser plate is inclined with respect to the central optical axis of the collected coherent light, the coherent light transmitted through the diffuser plate is incident on an integrator, and light is emitted from the integrator.