Projection screen and projection display system

Abstract

The invention relates to a projection screen and a projection display system, and the projection screen comprises a substrate, one side of the substrate is provided with a plurality of grid structures which are arranged in an array manner along a first direction, each grid structure is provided with a first reflection surface, and the first reflection surface and the first direction are arranged at an included angle; in the first direction, the multiple grid structures are symmetrically arranged along the first reference surface, in the first direction and in the direction away from the first reference surface, the included angle between the first reflecting surface of each grid structure and the first direction is gradually increased, and the height of each grid structure in the second direction is gradually increased; the first direction is perpendicular to the second direction, the first direction is perpendicular to the first reference plane, and the second direction is parallel to the first reference plane. The projection light reflected by the projection screen on the two side areas can be emitted to the visible area as much as possible, light loss is reduced, the brightness of the two side areas and the middle area of the projection screen is made to be uniform as much as possible, and the brightness uniformity of the projection screen is improved.

Description

Technical Field

[0001] The present application relates to the field of projection display technology, and in particular to a projection screen and a projection display system. Background Art

[0002] A projection display system requires a projector and a projection screen. The function of the projection screen is to image the image emitted by the projector and redistribute the projection light intensity. The projection screen's redistribution of the projection light intensity relies on various microstructures on the screen to diffuse or converge the projection light or control the transmission direction of the projection light as needed to meet the needs of different viewing fields. In related technologies, the projection screen has poor control over the transmission direction of the projection light, resulting in uneven brightness of images observed in different viewing fields, affecting the viewer's visual experience. Summary of the invention

[0003] Based on the above description, the present application provides a projection screen and a projection display system to solve the problem of uneven brightness of the current projection screen.

[0004] According to one aspect, the present application provides a projection screen, comprising: a substrate, one side of the substrate having a plurality of grid structures arranged in an array along a first direction, each of the grid structures having a first reflection surface, and the first reflection surface being arranged at an angle to the first direction; in the first direction, the plurality of grid structures are symmetrically arranged along a first reference surface, in a direction along the first direction and away from the first reference surface, the angle between the first reflection surface of each of the grid structures and the first direction gradually increases, and the height of each of the grid structures along a second direction gradually increases;

[0005] The first direction and the second direction are perpendicular to each other, and the first direction is perpendicular to the first reference plane, and the second direction is parallel to the first reference plane.

[0006] In one or more embodiments, along the first direction and in a direction away from the first reference plane, the width of each of the grid structures gradually decreases, and along the second direction, the maximum heights of each of the grid structures are the same; or

[0007] In the first direction and in a direction away from the first reference plane, the widths of the grid structures are the same, and along the second direction, the maximum heights of the grid structures gradually increase.

[0008] In one or more embodiments, the grid structure has an orthographic projection shape on the second reference plane that is a stripe;

[0009] The second reference plane is a plane perpendicular to the second direction.

[0010] In one or more embodiments, the width of the grid structure along the first direction is 5 μm to 80 μm; and / or

[0011] The maximum height of the grid structure along the second direction is 1 μm to 10 μm.

[0012] In one or more embodiments, in a direction along the first direction and away from the first reference plane, a difference in angles between two first reflection surfaces corresponding to two adjacent grid structures and the first direction is 0.000001°-0.00001°.

[0013] In one or more embodiments, the grid structure has a second reflective surface intersecting the first reflective surface;

[0014] The first direction is perpendicular to the second reflecting surface.

[0015] In one or more embodiments, the first reflective surface and the second reflective surface of the grid structure are both coated with a reflective film, and the material of the reflective film is aluminum or silver.

[0016] In one or more embodiments, the projection screen further comprises a diffusion layer disposed on one side of the plurality of grid structures of the substrate.

[0017] In one or more embodiments, the projection screen further includes a color adjustment layer disposed on one side of the plurality of grid structures of the substrate.

[0018] According to another aspect, the present application provides a projection display system, comprising a projector and a projection screen as described in any one of the aforementioned embodiments, wherein the projector is disposed toward a side of the plurality of grid structures of the substrate and passes through the first reference surface.

[0019] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0020] In the present application, one side of the substrate has a plurality of grid structures arranged in an array along a first direction, and in the first direction, the plurality of grid structures are symmetrically arranged along a first reference plane; in the direction along the first direction and away from the first reference plane, the angle between the first reflection surface of each grid structure and the first direction gradually increases, and the height of each grid structure along the second direction gradually increases. In this way, when the projector projects the projection light onto the projection screen, the reflected light on the two side areas of the projection screen is emitted as far as possible to the visible area, reducing light loss, making the brightness of the two side areas and the middle area of ​​the projection screen as uniform as possible, and improving the uniformity of the brightness of the projection screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the reflection of projection light of a projection screen in the related art;

[0022] Figure 2 A schematic diagram of projection light reflection of a projection screen provided in one embodiment of the present application;

[0023] Figure 3a A side view of a portion of the structure of a projection screen provided in another embodiment of the present application;

[0024] Figure 3b A side view of a portion of the structure of a projection screen provided in another embodiment of the present application;

[0025] Figure 4 for Figure 2 A top view of a portion of the structure in the projection screen;

[0026] Figure 5 for Figure 2 A three-dimensional schematic diagram of some structures in the projection screen;

[0027] Figure 6 A partial structural schematic diagram of a projection screen provided in an embodiment of the present application;

[0028] Figure 7 A schematic diagram of the visual range and horizontal viewing angle of the projection screen in an embodiment of the present application;

[0029] Figure 8 A schematic diagram of the visual range and horizontal viewing angle of a projection screen in the related art;

[0030] Fig. 9 A schematic diagram of the saturation and color reproduction of a projection screen according to an embodiment of the present application;

[0031] Fig.10 Schematic diagram of the saturation and color reproduction of the comparative projection screen. DETAILED DESCRIPTION

[0032] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] In related art, see Figure 1 , Figure 1The schematic diagram of the projection light reflection of the projection screen in the related art is shown; in the figure, the projection screen is divided into a left projection area L and a right projection area R, and the projection screen is coated with a diffuse reflection coating on the front of the film, so that the projection light is not effectively reflected to the visible area. The inventor found that when the projection light exceeds a certain angle, the projection light is reflected outside the visible area, which greatly reduces the brightness of the projection screen. Therefore, the left and right projection lights are reflected to both sides through the projection screen, resulting in uneven brightness seen by viewers G-1 and G-2. For example, projector Y emits projection lights PL, PRA and PR on the projection screen, and the left side of the projection screen emits reflected lights PL1, PL2, PL3, PL4 and PL5, and the middle and right sides of the projection screen also emit corresponding reflected lights. The viewer G-1 sees that the left area of ​​the projection screen is brighter than the right area, while the viewer G-2 sees that the right area of ​​the projection screen is brighter than the left area, with large light loss and low gain.

[0035] Based on this, the embodiments of the present application provide a projection screen and a projection display system to solve the problem of uneven brightness of the current projection screen.

[0036] Figure 2 FIG. 3 shows a schematic diagram of a projection light reflection of a projection screen provided in an embodiment of the present application, and FIG. Figure 2 A side view of a partial structure of a projection screen; for ease of explanation, only the portion related to the embodiment of the present application is shown.

[0037] See also Figure 2 As shown in Figure 3, a projection screen provided in an embodiment of the present application includes: a substrate L01, one side of the substrate L01 has a plurality of grid structures L0201 arranged in an array along a first direction F1, each grid structure L0201 has a first reflection surface (not shown in the figure), and the first reflection surface is set at an angle with the first direction F1; in the first direction F1, the plurality of grid structures L0201 are symmetrically arranged along a first reference surface (not shown in the figure), and in the direction along the first direction F1 and away from the first reference surface, the angle between the first reflection surface of each grid structure L0201 and the first direction F1 gradually increases, and the height of each grid structure L0201 along the second direction F2 gradually increases; the first direction F1 and the second direction F2 are perpendicular to each other, and the first direction F1 is perpendicular to the first reference surface, and the second direction F2 is parallel to the first reference surface.

[0038] It should be noted that the substrate L01 refers to a bottom plate, which can be made of a PET sheet or a PVC sheet, and the thickness can be selected from 0.1mm to 0.5mm. A plurality of grid structures L0201 are made on the substrate L01, and the plurality of grid structures L0201 and the substrate L01 can be an integrated structure. The plurality of grid structures L0201 are distributed in an array along the first direction F1 and are continuously arranged. Each grid structure L0201 has a first reflection surface, and the first reflection surface is arranged at an angle to the first direction F1, that is, the first reflection surface is an inclined surface, and the first reflection surface is arranged at an acute angle to the first direction F1. In the first direction F1, the plurality of grid structures L0201 are symmetrically arranged along the first reference plane, wherein the first direction F1 is parallel to the horizontal direction, the first reference plane refers to the symmetry plane, and the plurality of grid structures L0201 of the substrate L01 are arranged symmetrically about the first reference plane, so that the projection screen is divided into symmetrical left projection area L and right projection area R.

[0039] In this embodiment, in the first direction F1, multiple grid structures L0201 are symmetrically arranged along the first reference plane, and along the first direction F1 and in the direction away from the first reference plane, the angle between the first reflection surface of each grid structure L0201 and the first direction F1 gradually increases, and the height of each grid structure L0201 along the second direction F2 gradually increases. In this way, when projector Y projects projection lights 1, 2, 3, and 4 onto the projection screen, the reflected light on the two side areas of the projection screen is emitted to the visible area as much as possible, reducing light loss, so that viewers G-1 and G-2 can see that the brightness of the two side areas and the middle area of ​​the projection screen is uniform, thereby improving the uniformity of the brightness of the projection screen.

[0040] Continue reading Figure 2 In some embodiments, along the first direction F1 and in the direction away from the first reference plane, the width of each grid structure L0201 along the first direction F1 gradually decreases, and the maximum height of each grid structure L0201 along the second direction F2 is the same. Specifically, in this embodiment, by setting the width of each grid structure L0201 along the first direction F1 and in the direction away from the first reference plane to gradually decrease, the maximum height of each grid structure L0201 along the second direction F2 gradually increases. In this way, along the first direction F1 and in the direction away from the first reference plane, the angle between each grid structure L0201 and the first direction F1 gradually increases, which helps to make the projection brightness of the two side areas and the middle area of ​​the projection screen as uniform as possible.

[0041] Alternatively, along the first direction F1 and in the direction away from the first reference plane, the widths of the grid structures L0201 along the first direction F1 are the same, and the maximum heights of the grid structures L0201 along the second direction F2 gradually increase. Figure 2 and Figure 3aAs shown, in a specific embodiment, the plurality of grid structures L0201 can be regarded as a grid layer L02, the maximum height (maximum thickness) of the grid layer L02 remains unchanged, and along the first direction F1 and in the direction away from the first reference plane, the widths of the grid structures L0201 along the first direction F1 are the same, and the maximum heights of the grid structures L0201 along the second direction F2 gradually increase. Figure 2 and Figure 3b As shown, in another specific embodiment, multiple grid structures L0201 can be regarded as a grid layer L02, and along the first direction F1 and in the direction away from the first reference plane, the width of each grid structure L0201 along the first direction F1 is the same, and the maximum height of the grid layer L02 gradually increases. In this way, there are multiple implementations, so that along the first direction F1 and in the direction away from the first reference plane, the angle between each grid structure L0201 and the first direction F1 gradually increases, which helps to improve the uniformity of the brightness of the projection screen.

[0042] See also Figure 2 , Figure 4 and Figure 5 In some embodiments, the orthographic projection shape of the grid structure L0201 on the second reference plane (not shown in the figure) is a strip shape; the second reference plane is a plane perpendicular to the second direction F2. Specifically, the orthographic projection shape of the grid structure L0201 on the second reference plane is a strip shape, so that each grid structure L0201 is arranged in a longitudinal extension, and multiple grid structures L0201 are arranged in an array along the first direction F1, and in the first direction F1, multiple grid structures L0201 are symmetrically arranged along the first reference plane, thereby realizing the overall structure of the projection screen.

[0043] See also Figure 2 and Figure 6 In some embodiments, the width of the grid structure L0201 along the first direction F1 is 5 μm to 80 μm. Further, the maximum height of the grid structure L0201 along the second direction F2 is 1 μm to 10 μm. Further, in the direction along the first direction F1 and away from the first reference plane, the difference between the angles between the two first reflection surfaces corresponding to the two adjacent grid structures L0201 and the first direction F1 is 0.000001°-0.00001°.

[0044] In a specific embodiment, the substrate L01 has 20,000 to 40,000 grid structures L0201 arranged in an array along the first direction F1, and the width of each grid structure L0201 is optional from 5 μm to 80 μm, and the widths of each grid structure L0201 can be the same or different, which can be set according to actual conditions. Further, the height of each grid structure L0201 is optional from 1 μm to 10 μm, and the heights of each grid structure L0201 can be the same or different, which can be set according to actual conditions. Further, along the first direction F1 and in the direction away from the first reference plane, in two adjacent grid structures L0201, the angle between the first reflection surface of the latter grid structure and the first direction F1 is 0.000001°-0.00001° larger than the angle between the first reflection surface of the previous grid structure and the first direction F1, and the specific size can be set according to actual conditions. In this way, making a plurality of micro-structured grid structures L0201 on the substrate L01 helps to control the reflection direction of the projection light and improve the brightness of the projection screen.

[0045] In some embodiments, the grid structure L0201 has a second reflective surface intersecting with the first reflective surface; the first direction F1 is perpendicular to the second reflective surface. Specifically, each grid structure L0201 has an inclined surface and a vertical surface, the inclined surface intersecting with the vertical surface, the inclined surface is used to realize the first reflective surface, and the vertical surface is used to realize the second reflective surface, and by arranging the second reflective surface perpendicular to the first direction F1, the ambient stray light on the side of the projection screen can be reflected by the second reflective surface to reduce the influence of the ambient stray light on the brightness of the projection screen.

[0046] Continue reading Figure 6 In some embodiments, the first reflection surface and the second reflection surface of the grid structure L0201 are coated with a reflection film L03, and the material of the reflection film L03 is aluminum or silver. In a specific embodiment, a coating process is used to coat a 400-500 angstrom aluminum film on the surface of the grid structure L0201. In this way, the reflectivity of the projection screen is effectively increased.

[0047] In some embodiments, the projection screen further includes a diffusion layer L04 disposed on one side of the plurality of grid structures L0201 of the substrate L01. Specifically, the raw material is prepared by mixing transparent resin, matting powder and curing agent, and then coated on one side of the plurality of grid structures L0201 of the substrate L01 to prepare the diffusion layer L04, and the roughness of the diffusion layer is optional at 0.1 to 1. In this way, the reflected light is diffusely reflected by the diffusion layer, so that the projection screen has a good visual effect.

[0048] Continue reading Figure 6In some embodiments, the projection screen further includes a color adjustment layer (not shown) disposed on one side of the plurality of grid structures L0201 of the substrate L01. Specifically, the color adjustment layer is prepared by mixing acrylic resin and red, green, and blue powders to prepare raw materials, and is applied to one side of the plurality of grid structures L0201 of the substrate L01, and the color adjustment layer is located between the reflective film L03 and the diffusion layer L04. In this way, the reflectance ratio of the projection screen to the red, green, and blue projection light of the projector Y can be increased, and the color saturation can be improved.

[0049] In some embodiments, the projection screen further includes a back adhesive layer L1 and a separation film L2, wherein the back adhesive layer L1 is disposed on a side of the substrate L01 away from the color adjustment layer, and the separation film L2 is disposed on a side of the back adhesive layer L1 away from the substrate L01. In this way, the projection screen can be directly attached to the wall, which is convenient and efficient to operate.

[0050] In some embodiments, the method for making a projection screen is carried out according to the following steps: 1. Nano-scale photolithography machine photoresist plate: the designed projection screen grid structure L0201 is engraved on a glass plate with photosensitive adhesive (i.e., photoresist plate) by a photolithography machine; 2. Copying the PET master: the grid structure L0201 on the photoresist plate is transferred onto a PET film by transfer replication technology to form a PET master; 3. UV transfer PET film: the PET master is attached to the embossing plate roller on the UV transfer equipment for UV transfer to produce a grid projection film roll; 4. Aluminum plating: the grid projection film roll is coated with an aluminum layer with a thickness of 400-800 angstroms on the grid surface by vacuum aluminum plating. 5. Apply the coloring layer: apply a coloring layer on the surface of the aluminum-plated layer; 6. Apply the diffusion layer: apply a diffusion layer on the surface of the coloring layer; 7. Apply the self-adhesive composite release film L2: 7. Apply a layer of self-adhesive on the back of the projection film to facilitate the projection film to be pasted on the surface of other objects; 8. Cutting: cut the projection film roll according to the designed projection film size.

[0051] It should be noted that the microstructure of the projection screen in the related art is basically produced by machining a master plate and completing it through a hot pressing process, while in the embodiment of the present application, a nano-level photolithography machine is used to perform grayscale photolithography technology, replicate the master plate, and UV transfer PET film to complete the microstructure production. In this way, the production process is simpler and the microstructure unit precision is higher.

[0052] Furthermore, in the related art, the optical structure of the high-gain projection screen usually uses glass beads, micro-steel beads, grids, Fresnel, and honeycomb lenses as the optical layer, while the embodiment of the present application uses an array-arranged grid structure L0201, which can increase the gain of the projection screen to 1.5-2.5, providing the best viewing effect for viewers at different angles within the observation range.

[0053] Based on the same inventive concept, an embodiment of the present application further provides a projection display system, comprising a projector Y and a projection screen of any of the aforementioned embodiments, wherein the projector Y is disposed on one side of the plurality of grid structures L0201 of the substrate L01 and passes through a first reference surface.

[0054] Specifically, the projector Y is arranged on one side of the multiple grid structures L0201 facing the substrate L01 and passing through the first reference plane. In the first direction F1, the multiple grid structures L0201 are symmetrically arranged along the first reference plane, and along the first direction F1 and in the direction away from the first reference plane, the angle between the first reflection surface of each grid structure L0201 and the first direction F1 gradually increases, and the height of each grid structure L0201 along the second direction F2 gradually increases. In this way, when the projector Y projects the projection line onto the projection screen, along the first direction F1 and in the direction away from the first reference plane, the projection light reflected by the projection screen on the two side areas is gradually emitted to the visible area, reducing light loss, making the brightness of the two side areas and the middle area of ​​the projection screen as uniform as possible, and improving the uniformity of the brightness of the projection screen.

[0055] In this embodiment, see Figure 7 , Figure 7 The schematic diagram shows the visible range and horizontal viewing angle of the projection screen in the embodiment of the present application. The projection light LP is controlled to reflect by the grid structure L0201. The angle R1 between the reflected light LP1 and the reflected light LPn is the optimal horizontal viewing angle, and they are bilaterally symmetrical. Figure 8 , Figure 8 The schematic diagram shows the visual range and horizontal viewing angle of the projection screen in the related art. The projection light LP is reflected by the grid control, and the angle R1 between the reflected light LP1 and the reflected light LPn is the optimal horizontal viewing angle. Figure 7 and Figure 8 It can be found that more reflected light is reflected from both sides of the projection screen LR of the embodiment of the present application to the observation area E, and the projection picture viewed at each position has uniform brightness, which effectively improves the viewer's visual experience.

[0056] In this embodiment, the projection screen of this embodiment and the projection screen of the comparative example are tested. The comparative example adopts the projection screen of Tiying Media, and the test is performed according to the following test steps: 1. Fix the projector and the projection screen of this embodiment, and adjust the projector so that the projected image is within the projection screen (projected image size: 91*34cm); 2. Fix the brightness and chromaticity tester, and the vertical distance between the brightness and chromaticity tester and the projector is 50CM; 3. Project a pure white image, move the brightness and chromaticity tester horizontally to the test point, measure the brightness of each test point (a total of 30 test points), and make a record; 4. The projector projects red, green, and blue pure color pictures at the test point F1 to measure the corresponding brightness and chromaticity, and make a record; 5. Replace the projection screen of this embodiment with the projection screen of the comparative example, measure the brightness and chromaticity according to step 3 and step 4, and make a record; 6. Compare the test parameters of the projection screen of this embodiment and the projection screen of the comparative example at the corresponding test points, and obtain the reflectivity of the projection screen of this embodiment and the projection screen of the comparative example at each point.

[0057] Table 1

[0058]

[0059] Refer to Table 1, which is a reflectivity test comparison table of the projection screen of the embodiment of the present application and the projection screen of the comparative example, wherein there are 30 test points distributed in an array, A1, A2, A3, A4 and A5 are a row of test points distributed at intervals of 20 cm along the first direction F1, and A1, B1, C1, D1, E1 and F1 are a column of test points distributed at intervals of 20 cm along the second direction F2. It can be seen from the analysis that at each test point, the reflectivity of the projection screen of the present embodiment far exceeds the reflectivity of the projection screen of the comparative example, and the reflectivity is the main parameter that directly reflects the brightness of the projection screen.

[0060] In addition, see Fig. 9 and Fig.10 , Fig. 9 A schematic diagram showing the saturation and color reproduction of a projection screen according to an embodiment of the present application is shown. Fig.10 The schematic diagram of the saturation and color reproduction of the comparative projection screen is shown. In the figure, the red circles represent the reference coordinates of the red, green, and blue pure color pictures projected by the projector at the test point F1, and the black circles represent the reference coordinates of the red, green, and blue pure color pictures reflected back by the projection screen. By comparison Fig. 9 and Fig.10 The saturation of the projection screen of this embodiment is obviously better than that of the projection screen of the comparative example, and the color reproduction degree of the projection screen of this embodiment is higher than that of the projection screen of the comparative example.

[0061] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A projection screen, characterized in that: include: A substrate, wherein one side of the substrate has a plurality of grid structures arranged in an array along a first direction, each of the grid structures having a first reflection surface, and the first reflection surface is arranged at an angle to the first direction; in the first direction, the plurality of grid structures are symmetrically arranged along a first reference surface, and in a direction along the first direction and away from the first reference surface, the angle between the first reflection surface of each of the grid structures and the first direction gradually increases, and the height of each of the grid structures along a second direction gradually increases; The first direction and the second direction are perpendicular to each other, and the first direction is perpendicular to the first reference plane, and the second direction is parallel to the first reference plane.

2. The projection screen according to claim 1, characterized in that: In the direction along the first direction and away from the first reference plane, the width of each grid structure along the first direction gradually decreases, and the maximum height of each grid structure along the second direction is the same; or In the direction along the first direction and away from the first reference plane, the widths of the grid structures along the first direction are the same, and the maximum heights of the grid structures along the second direction gradually increase.

3. The projection screen according to claim 1, characterized in that: The orthographic projection shape of the grid structure on the second reference plane is a strip shape; The second reference plane is a plane perpendicular to the second direction.

4. The projection screen according to claim 1, characterized in that The width of the grid structure along the first direction is 5 μm to 80 μm; and / or The maximum height of the grid structure along the second direction is 1 μm to 10 μm.

5. The projection screen according to claim 1, characterized in that: In a direction along the first direction and away from the first reference plane, a difference between angles between the two first reflection surfaces corresponding to two adjacent grid structures and the first direction is 0.000001°-0.00001°.

6. The projection screen according to any one of claims 1 to 5, characterized in that: The grid structure has a second reflective surface intersecting with the first reflective surface; The first direction is perpendicular to the second reflecting surface.

7. The projection screen according to claim 6, characterized in that The first reflection surface and the second reflection surface of the grid structure are both coated with a reflection film, and the material of the reflection film is aluminum or silver.

8. The projection screen according to any one of claims 1 to 5, characterized in that: The projection screen further includes a diffusion layer disposed on one side of the plurality of grid structures of the substrate.

9. The projection screen according to any one of claims 1 to 5, characterized in that: The projection screen further comprises a color adjustment layer arranged on one side of the plurality of grid structures of the substrate.

10. A projection display system, characterized in that: The method comprises a projector and a projection screen as described in any one of claims 1 to 9, wherein the projector is arranged toward one side of the plurality of grid structures of the substrate and passes through the first reference surface.

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