User manual AUTODESK LIGHTSCAPE

[. . . ] /LJKWVFDSH OE $SULO#4<<< 31#93<36034333308355 Copyright © 1993-1999 Autodesk, Inc. All Rights Reserved This publication, or parts thereof, may not be reproduced in any form, by any method, for any purpose. MAKES NO WARRANTY, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, REGARDING THESE MATERIALS AND MAKES SUCH MATERIALS AV AILABLE SOLELY ON AN "AS-IS" BASIS. BE LIABLE TO ANYONE FOR SPECIAL, COLLATERAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES IN CONNECTION WITH OR ARISING OUT OF PURCHASE OR USE OF THESE MATERIALS. [. . . ] Goniometric Diagrams Photometric data is often depicted using a goniometric diagram. This type of diagram visually represents how the luminous intensity of a source varies with the vertical angle. However, the horizontal angle is fixed and, unless the distribution is axially symmetric, more than one goniometric diagram may be needed to describe the complete distribution. the photometric center, measured along a line leaving the center in the specified direction. Goniometric diagram converted to a photometric web Example 1: Isotropic Distribution A sphere centered around the origin is a representation of an isotropic distribution. All the points in the diagram are equidistant from the center and therefore light is emitted equally in all directions. Goniometric diagram Lightscape extends the goniometric diagram to three dimensions, so that the dependencies of the luminous intensity on both the vertical and horizontal angles can be examined simultaneously. The center of the photometric web represents the center of the luminaire. The luminous intensity in any given direction is proportional to the distance between this web and Isotropic distribution Example 2: Ellipsoidal Distribution In this example, the points in the negative Z direction are the same distance from the origin as the corresponding points in the positive Z direction, so the same amount of light shines upward and downward. No point has a very large X or Y component, 150 Lightscape Creating and Editing Photometric Webs either positive or negative, so less light is cast laterally from the light source. Creating and Editing Photometric Webs Use the Photometric Web editor to customize photometric webs that you can associate with the luminaires in your model. You can create photometric webs or modify existing ones. Using the Photometric Web Editor You can use the Photometric Web editor to create a photometric web by adding and then editing control points and their associated distribution curves. Use the Zoom and Orbit buttons to change your view of the photometric web. Ellipsoidal distribution To display the Photometric Web editor: Choose Light | Photometric Web. Example 3: Complex Distribution You can use the photometric web to create very complex light distributions, including ones that are unlikely to be used in reality, as shown in the following illustration. The Photometric Web editor appears. The Photometric Web editor contains the following components: Mode Use the Mode list to set the current control point mode. Select: Unusual and unlikely distribution To: Edit Change the shape of the diagram by dragging existing points in the web. 151 9 Photometrics Select: To: Insert Add new control points by dragging the cursor along an existing distribution curve and clicking a location. Distribution curves associated with the point are also deleted. Vertical Angle Enter a value in the Vertical Angle box to move the current control point and distribution curve to the specified vertical angle. Intensity (abs) Enter a value in the Intensity (abs) box to set the absolute intensity of the selected control points. Intensity (rel) Enter a value in the Intensity (rel) box to display the intensity relative to the photometric web diagram. Multiplier The value you enter in the Multiplier box defines the ratio between the absolute and relative intensities. The multiplier value can be any positive real number. Delete Symmetry Use the Symmetry list to enforce the specified symmetry on the photometric web. Select: To: Axial Set the distribution to the same value around all 360 degrees of the light source's vertical axis. Specify no symmetry. Quadrant Mirror 0-180 None Saving Photometric Webs You can save customized photometric webs as IES files, which can then be assigned to a luminaire. To save a photometric web as an IES file: Hemisphere Use the Hemisphere list to control in which hemispheres the light is distributed. For more information, see "Customized Photometric Web Example" on page 153. Click Save As on the Photometric Web editor. Bottom Top Both Shine light down only. Enter the path and filename of the IES file, then click OK. Horizontal Angle Enter a value in the Horizontal Angle box to move the current control point and distribution curve to the specified horizontal angle. The Photometric Web is saved to the specified file in the IES format. Note: You can also use the LID conversion utilities to convert your LID to other file formats. For information, see "Using LID Conversion Utilities" on page 155. 152 Lightscape Customized Photometric Web Example Resetting Photometric Webs You can reset a photometric web to the default LID in the Photometric Web editor. To reset a photometric web: 2. In this example, we will create a light that only shines downwards. 1. Click the Orbit button until you can see the appropriate area of the Photometric Web editor. The Open dialog appears. 2. In the Open dialog, locate the following IES file: lightscape\lib\lights\lvs\ default. ies 3. [. . . ] A color with a low saturation is very close to gray. scroll A technique for computing radiosity solutions that starts with the direct illumination and then computes more and more of the indirect illumination until the solution converges. radiosity A camera motion parallel to the screen. In perspective view, the focus point remains the same but the screen is tilted with respect to the view direction. self-emitted luminance A technique for solving the global illumination problem for diffuse environments. ray offset Luminance emitted from a surface that is not due to reflection of incoming light off that surface. shadow ray The displacement measured from the origin of a shadow ray. Intersections between a surface and a shadow ray closer to the origin than the ray offset amount are discarded. ray tracing A line cast between a point on a light source and a point on a receiving surface to determine the possible presence of occluders that would prevent light from the source from reaching the receiving surface. SI units A way of computing an image based on tracing paths of light from the eye back to the luminaires. reflectance International System of Photometric Units. sky conditions The ratio of the luminous flux reflected off a surface to the luminous flux incident on it. reflection The conditions of the sky at a given time and location; described as the fraction of the sky covered by clouds or as clear, partly cloudy, or cloudy sky. skylight Light incident on one side of a surface leaving it from Light energy from the sun that reaches the scene after 331 Glossary scattering through the atmosphere. smoothing angle The angular threshold used during automatic computation of vertex normals. Polygons incident on a vertex share a vertex normal only if their respective surface normals form an angle that is less than the given threshold. soft shadow its axis, and whose intensity drops smoothly away from this axis. [. . . ]