illumination in lighttools - the menon group · •each receiver type can have several () ¦ ¦ = =

4/26/2012

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Introduction to LightTools TrainingIllumination in LightTools Ɣ

Copyright © 2012 Synopsys, Inc.

Illumination in LightTools

© Synopsys 2012 1 Introduction to LightTools, “Illumination in LightTools”

We’ll use LightTools to review fundamental concepts in illumination


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LightTools Models the Interaction of Rays with Simulated Surfaces

ScatterRays can:

Refract

Reflect

Ab b


TIR

Absorb

Optical Properties Are Important!• Geometry alone does not determine light distribution• Optical Properties determine how the energy and direction

of a ray changesy g• Example: H7 Automotive lamp


All surfaces TIR With correct surface properties

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The Optical Properties in a Model Are Defined in the Optical Properties Manager

• Property zones choose from one of the optical properties in the OPM

• Use the OPM to:– Manage optical properties– Make changes to the model properties– Determine the list of current optical property assignments


Determine the list of current optical property assignments– Visualize the optical property assignments

The Optical Property Manager Interface Includes:

A list of existing Model and Default Properties

Controls for creating, loading


Controls for defining the optical property itself

and saving Model Properties

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OPM Navigation Tree Listing

• The OPM list is found in the system navigator

• Contains two sections– Model Properties: All of the optical

properties currently defined for the model– Default Properties: Optical property

definitions that are used when new surfaces are created (moved from the Preferences


are created (moved from the Preferences dialog box)

Assigning an Optical Property

• After an optical property is defined in the Model Properties list of the OPM, it will be available to be assigned to any property zoneproperty zone

• Assignment is made either through various context-sensitive menus or on the Property

Context menu


on the PropertyZone tab

List of available Model Properties

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Property Zone Tab

• The Property Zone tab displays several controls and summary information

Number of zones sharing this property

Drop-down for assigning optical properties

Open and Create controls similar to context menu


controls

Key summary information on current optical property

Editing Optical Properties

• Optical property definitions are freely changeable in the OPM

Modifications apply to all property• Modifications apply to all property zones currently assigned to that property

• The number of property zones that currently have the optical property assigned is shown in parentheses after the name of the property


the name of the property

• Properties in the Model Properties list can be deleted only when they are not assigned to any property zone– Use the context menu or the Delete key

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Usage Tab• A new Usage Tab provides summary tables for optical

property usage– Usage tabs are available for the whole model, each optical property,

and each entitand each entity

• The individual property usage tables show all the property zones to which the property is currently assigned– Shows the Solid, Primitive, Surface, and Zone names– Table can be sorted by column, as with any LightTools table

• The Model Properties usage tab displays all the zones in the model and their assigned optical properties


ode a d t e ass g ed opt ca p ope t es• Filter fields are provided at the top of the table

– Filters work on substrings - no wildcards needed

• User can select multiple rows and use the right-click context menu to change the assigned optical property for those zones

Usage TabSearch string filter fields


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Custom Colors

• There are two modes for displaying surface colors in the 3D Design view

By Refract Mode: Displays the colors as a function of property– By Refract Mode: Displays the colors as a function of property type – identical to previous version of LightTools

– By Optical Property: Displays a user-defined color for each property zone


• To toggle between the two modes, use the menu View > Surface Color

Custom Color Example

By Refract Mode

By Optical Property


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Work Along: Confirm Snells Law

• Snell’s law is:

• Air index of refraction (nair) is ~1.000

no*sin(ƍo)=n1*sin(ƍ1)no non1

ƍo ƍ1

ƍo


• Let’s make sure LightToolsagrees…

Start by Making a Block…• Enter the following:

– Block3Pt xyz 0,0,0 1 0.1

• Right click on it to open the optical properties. Check that it is Smooth optical and rays transmit


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Non-Sequential (NS) Rays Can Be Used to Verify the Correct Interaction of Rays at Surfaces

� Each Non-Sequential ray starts with a relative power of 1.0

� The ray’s power drops at each f d t th t itt d

• Trace an NS ray through your block at an AOI 10o

– XYZ 0 0 -0 5 surface due to the transmittance and reflectance � Fresnel loss, scattering losses, and bulk

absorption are all taken into consideration

� Can trace individual rays, fans of rays, or grids of rays

XYZ 0,0, 0.5– Alpha: 10o


Why Did They Stop?• Each of the three rays shown below stops for a

different reasonTop Surface: Max Hits = 5

Surface set to absorb

Max Hits = 5

5

1

4

3

2

Surface set to split


Ray misses all other surfaces

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Ray Properties• Most properties are defined for the entire fan or grid of

rays, and are read-only for the individual segmentsRay stops when its power d b l 1%

Automatic: check if the surrounding region has amaterial

Description of

drops below 1%


pray fan

Wavelength for NSRays• Use Spectral Region Preferences to enter spectrum

Right-click in row to access menuaccess menu

LightTools can generate Blackbody


g yand Gaussian spectral distributions

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Accessing Ray Trace Data• Single ray trace data is very useful for troubleshooting


An NSRay traced through a light pipe (Fresnel Loss & Split)

Confirm the Behavior of an NS Ray through the Block• In the NS ray’s properties,

check the Incidence and Exit Angles of segment_1

• Does this make sense?– Check the Properties Tab of

this segment– Incidence: 10o

– Exit: 6.57o

g– nNBK7(550nm) = 1.5185– Snells law predicts 6.57o

Index following the interface


Incidence and Exit angles

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On a Real Optical Interface, Transmittance of Ray Will Drop Due to Fresnel Reflectance

• Currently, our ray transmits 100%– Fresnel reflectance is not

accounted for…yet! Current ray transmittance 100%

Fresnel Reflectance

Curves


Source: Wikipedia (http://en.wikipedia.org/wiki/Fresnel_equations)

Modify the Optical Property to Account for Fresnel Losses

• Open the Optical Properties Manager by double-click on it in the system navigator

• In the Model Properties> Transmitting>Smooth Optical window, change the Advanced Properties to Fresnel Loss– Press OK

Note that ALL 6 transmitting surfaces


– Note that ALL 6 transmitting surfaces will account for Fresnel losses

• Re-check the transmittance of the NS ray at segment_1

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Property Zones Let You Specify Different Optical Properties over a Surface

Refracting gproperty zone


Reflecting property zone

Work Along: Make a Lens…• Start a new model

(File>New)

• Enter the command:– Sketch4PtLens xyz 0,0,0

xyz 0,10,2 xyz 0,10,4 xyz 0,0,6 xyz 0,0,1


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…add an NS ray fan…

• Add an NS ray fan– NSFanAIM xyz 0,-9,-5 xyz

0,9,-5 xyz 0,9,0y– Change it to a fan of 21 rays in

the Properties window


…and a dummy plane

• Add a dummy surface near the focal point so the NS rays are longer in the 3D window

• Dummy planes are defined by a vector that is normal to the plane

1st point

Plane

– DummyPlane xyz 0,0,30 xyz 0,0,20 • The length of the

vector is the half-diameter of the plane

2nd point


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Surfaces Can Have None, One, or Multiple Property Zones Associated with Them• Each property zone can have a

different optical property

• All surfaces in LightTools have a BareSurface zone– An additional property zone is

automatically added to lens primitive surfaces

• Property zones supersede the B S f


BareSurface zone

• Additional property zones can be added to any surface by right clicking on the surface and choosing “Add Property Zone”

Add a Mirror Optical Property

• Right click on the LensFrontSurface and select Create and Assign gNew Optical Property– Make the new optical

property a Simple Mirror– Rename the optical

property to “Mirror”


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Make the Center of the Lens Reflective by Changing the Optical Property of zone_1• Switch the optical

properties of LensFrontSurface>

BareSurface

BareSurface back to Transmitting_1

• LensFrontSurface>zone_1 should be the mirror– In the Geometry tab,

change the Radius to 5mm

zone_1


When Rays Split, Each Path Is Traced

• The power of each ray depends on reflectance and transmittance of the

90% transmittance 10% reflectance

and transmittance of the optical property 10 rays transmit.

With 90% power


10 rays reflect. With 10% power

10 rays start, which split into 20 rays (power is maintained)

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Probabalistic Ray Tracing Will Trace 1 Path

90% transmittance 10% reflectance

• Path of ray is determined probabilistically

9 out of 10 rays transmit. With 100% power

– Probability is determined by the transmittance and reflectance of the optical property

– Each path gets 100% power


1 out of 10 rays reflect. With 100% power

When You Need to Keep Track of Both Paths, Probabilistic Ray Tracing Is Efficient

All surfaces: Fresnel splitMax hits = 100Ray threshold = 1e-10

Receiver planeBacklight example

Probabilistic Ray Split: NO Probabilistic Ray Split: YES1 NS ray started in each model

y

Reflector and source

“Sawtooth” grating


2,000 rays started277,948 rays at receiverSimulation time: 50 minError estimate: 42%

2,000 [200,000] rays started 1,247 [118,969] rays at receiverSimulation time: 19 seconds [29 min]Error estimate: 44% [6%]

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The Distribution from a Real Light Source Is Simulated by Tracing Monte Carlo Rays

• These rays are accumulated on receivers, and are used to compute illumination analysis metrics– Illuminance: Spatial distribution of power– Intensity: Angular distribution of power– Luminance: Both angular and spatial components


Illuminance is Power/Area

• …or the spatial distribution of power• Photometric units: lux (lm/m2)• Radiometric units: W/m2


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Work Along: Illuminance in Space• Start a new model (File>New)

• Add a cylinder source at the origin:y g– XYZ 0,0,0– Radius: 1– Length: 0.1


Add Two Dummy Planes, and Add Receivers• Add two dummy planes

– One at Z=10, the other at Z=20– Width = Height = 10mm for both– DummyPlane xyz 0,0,10 xyz 0,0,15– DummyPlane xyz 0,0,20 xyz 0,0,25– Right click and “Add Surface

Receiver”


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We’ll Investigate Illuminance Differences Between the Two Dummy Planes• To define the cone, we’ll

specify the aim sphere of the sourcethe source

• Right click on the CylinderSource and go into Properties– In the emittance tab, change

M d O t Ai


Measured Over to Aim Region

– In the Aim Sphere tab, change the lower angle to 10o.

You Can Specify a Source to Emit Rays into a Specified Region to Trace Only the Rays You Care About

Aim areaAim sphere

Ray angles are confined to the aim cone

Rays trace into the aim area


Aim regions do not affect the relative power distribution from the source!

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Aim Sphere Controls• Upper angle

– Measured from +Z axis to –Z axis of aim sphere,

Z

U

Rays not emitted inthis region

mainly to clip the region defined by Lower Angle

• Lower Angle– Measured from +Z axis

to –Z axis of aim sphere

• Upper Angle < Lower Angle

Lowerangle

Upperangle

Rays emitted intothis annular zoneAim Sphere

Source


Angle• Collimated source:

– Upper angle = 0– Lower Angle = 0

Rays not emitted inthis region

Aim Sphere Limits…

To cover the whole sphere:upper = 0°, lower = 180°, alpha = any number, beta = any number

To cover the “upper” hemisphere:upper = 0°, lower = 90°, alpha = 90°, beta = 0°

To cover the “lower” hemisphere: upper = 0°, lower = 90°, l h 90° b t 0°


alpha = -90°, beta = 0°

To cover the “forward” 20°:upper = 0°, lower = 10°, alpha = 0°, beta = 0°

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Run a Simulation…

• Go to Ray Trace>Begin All Simulations


• To toggle the visibility of simulation rays in the 3D window:

Go to Ray Trace>Simulation Input, and press Begin Forward Simulation

Go to Ray Trace>Begin All Simulations

There Are Three Ways to Start a Simulation

Use the Begin Simulation icon in the 3D window

12


3

Modify simulation inputs…

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Analyzing the Illuminance

• Rename the receivers to:– “10mm Receiver”– “20mm Receiver”20mm Receiver

• Go to Analysis>IlluminanceDisplay>Lum Viewer– Pick the closer reciever

and press OK

10mm

20mm


and press OK

To switch receivers in the LumViewer…

View the Illuminance Pattern in the 3D Window• Right click on each

receiver and choose “Show Simulation Data”

• Visualizing illuminancedata in the 3D window is available for data on“Show Simulation Data” available for data on dummy plane receivers


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Illuminance Data and Statistics Can Be Viewed in the Illuminance Mesh Properties• Right click on each receiver to get to the illuminance

mesh’s properties

Error statistics (more later)

Total power ll d b


Raw mesh data

collected by the mesh

Mesh statistics

Intensity Is Power/Solid Angle• …or the angular distribution of power• Photometric units: Candela (lm/sr)• Radiometric units: W/sr• Radiometric units: W/sr


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The Intensity Over Collected by Our Two Receivers Is Identical!• Go to Analysis>Intensity

Display>LumViewer

Z=10mm Z=20mm


Intensity meshes only use the angular information from each

ray…in this case, both receivers collect the same data

Luminance Is Power/Area/Solid Angle• Collect power as a function of spatial

position and angular direction– “Brightness” is our perception of luminance

• Photometric units: Nits (lm/m2/sr)

• Radiometric units: W/m2/sr


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Spatial vs. Angular Luminance

• Spatial Luminance Meter– Collect rays over a spatial

region, and limit the angle

• Angular Luminance Meter– Collect rays over an entire

hemisphere, and limit the – Like a spot meter area

Luminance collected using

fixed area

Luminance collected


Plotted as a function of angle

Luminance collected using a fixed or scanning angle

Plotted as a function of spatial position

Model a Thin Diffuser Using a Thin Block with a Lambertian Scatterer• Open the Optical Properties

Manager. Add a Simple Scatterer> Lambertian– In the Lambertian tab, change

the ray trace mode to transmit– A lambertian scatterer scatters

light with uniform luminance over the entire hemisphere

• Make a thin block just in front of the first receiver


– Block3pt xyz 0,0,9.8 10 0.1– Make the material air

• Change the optical property of the Block’s RightSurface to Lambertian

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Run a Simulation and Compare the Intensity and the Angular Illuminance• In the Receiver

Properties>Forward Simulation enable a spatialSimulation, enable a spatial and angular luminance chart for each receiver

• Run a simulation with 100,000 rays

• Go to Analysis>Intensity>LumViewer


• Go to Analysis>Angular Luminance>LumViewer

Intensity vs. Illuminance vs. Luminance of a Lambertian Scatterer10mm Receiver The adjacent receiver collects nearly all angles

Intensity Angular Luminance Illuminance Spatial

Luminance


20mm Receiver The spacing between the receivers limits the cone of collected rays

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How Are Rays Collected on a Receiver Mesh?• Receiver data is usually divided into rectangular grids to

analyze ray data• Data can be displayed as numbers/color maps

Rays on receiver Îprobably not very useful form for analysis

Receiver surface is divided into a rectangular grid (# rays/cell is shown)


(Ray power)/ (# Samples) for each cell

(Ray power)/ (# Samples) as a false color map

Importance of Mesh Size• Mesh dimensions (size) control the “resolution” and

“accuracy” of the results2 mm 2 mm

2 m

m


5x5 Mesh Î larger cells Îlower spatial resolution (0.4 mm)2 and more rays per cell Îhigher accuracy

8x8 Mesh Î Smaller cells Î Higher spatial resolution (0.25 mm)2 and fewer rays per cell Î lower accuracy

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Receiver Mesh Types• Each receiver type can have several

types of “meshes”– Different meshes for different types of

data

• Surface receiver– Illuminance mesh (Irradiance,

Illuminance)– Intensity mesh (Intensity)– Spatial luminance mesh (Luminance)

Angular luminance mesh (Luminance)


– Angular luminance mesh (Luminance)– CIE meshes (Chromaticity and CCT)

• Far field receiver– Intensity mesh (Intensity)– CIE meshes (Chromaticity and CCT)

The Accuracy Is Determined by the Number of Rays Falling in Each Bin (Ray Density)• Every cell in the mesh has a certain error due to statistical

noise. The peak error estimate is the first standard deviation of the receiver cell with the maximum illuminance or intensityof the receiver cell with the maximum illuminance or intensity value and is given by the following formula:

( )¦¦

N

N

f

f=

2

!N

= 1!

Converges when f is constant


where f = irradiance or intensity of each ray

N = total number of rays traced from one source

This is the Error Estimate for each bin

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54% of 5,000 rays11 x 11 gridPeak error 16.8%

54% of 5,000 rays5x 5 gridPeak error 8.9%

54% of 240,000 rays11x 11 gridPeak error 2.9%

Binning Effects


• Note the tradeoff between spatial resolution (grid size) and peak error

• Larger numbers of rays must be traced to get enough rays per bin for better accuracy

Rays That Are Below the Relative Ray Power Threshold Will Be Terminated• As a ray interacts with your

model, there will typically be l t h flosses at each surface interaction and through many volumes

• The Relative Ray Power Threshold controls the threshold that the power of a

d t b f it iWhen you have significant scattering in your model


ray can drop to before it is terminated

• For a simulation, this control is available in the Ray Trace>Simulation Inputs…– The default is 1%

scattering in your model, consider this threshold

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Working with LightTools Geometry

• Coordinate systems

• Entities/primitives

• Euler angles


• Ray Trace Acceleration

Coordinate Systems� LightTools has a global coordinate system and a

local coordinate system (also known as UCS, or user coordinate system)y )� By default they are coincident� Both coordinate systems are right-handed

Global Coordinate System


Local Coordinate System (or UCS)

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Surface Coordinate System� Each surface has a local coordinate system identified

with it� The z-axis of each surface coordinate system points

d f h lidoutward from the solid� Place UCS on surface to see coordinate system

orientation

Place UCS on surfaceReturn UCS to global


Global coordinatesystem(black axes)

Local coordinate system(colored axes)

User Coordinate System - UCS � The UCS can be shifted and rotated with respect to

the global coordinate system with UCS Preferences � View > View UCS > UCS Preferences or� UCS tab of the 3D view preferences


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Defining New UCS� The UCS axes can also be

aligned with the coordinate system of a surface or ray using the command palette

� Sketched objects are entered aligned with or oriented relative to the UCS Z-axis.� Useful for entering tilted

subsystems

Move origin

Rotate aboutorigin

Place on reference


Place on surface

Mouse clicks:define origin & 2coordinate axes

Place on line

coordinate system

Point Entry Is Very Flexible� LightTools keeps track of the location of the

current point (location of the last point entered)

� A new point can be entered in absolute terms or as a change (delta) from the current point

� Points can be entered in global, UCS, or pane coordinates


coordinates

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How to Enter Points on the Command Line� The basic command for entering a point globally is

XYZ x,y,z

� The x, y, z coordinates are separated by commas (no white space)space)

� White space is used before and after the coordinates� Points can also be given in UCS (local) coordinates

LXYZ x,y,z

� Points can also be given in pane coordinatesUVW u,v,w

� U is horizontal in the pane V is vertical in the pane W is


� U is horizontal in the pane, V is vertical in the pane, W is perpendicular to the pane

� All forms are converted internally to XYZ form

Entering Points Relative to Current Point

� A point can also be expressed as a change (delta) l ti t th t i t i l b l l lrelative to the current point in global, local, or pane

coordinates� The delta can be a linear delta or a length and an angle

� Linear delta formsDXYZ dx,dy,dz delta in global coordinatesLDXYZ dx,dy,dz delta in local coordinatesDUV d d d d lt i di t


DUV du,dv,dw delta in pane coordinate

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Entering Points as Angular Deltas� Points can also be entered as length and angle from

current point� Most useful form:

LA l," delta length and angle (in pane)

o

90o

"


0o

la 2,0 la 1,45 la 2,0 la 1,90 la 1,0

Point Entry ExamplesXYZ 0,0,0 global origin

UVW 0,0,0 origin in pane (keep depth)

DXYZ 1,2,3 shift 1 in x, 2 in y, 3 in z (global)

DUV 1,2,0 shift 1 right, 2 up in pane (keep depth)

LA 2,45 shift length 2, 45° in pane

; repeat last entered point (global)


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Euler Angle Rotations• Rotations described by the optical Euler angles:

– Order is important! For multiple angles, Alpha rotation 1st, then Beta about the newly defined axes, then Gamma about the axes resulting from the Alpha and Beta rotationsresulting from the Alpha and Beta rotations

– Convention:í Alpha: positive for “+Z to +Y”í Beta: positive for “+X to +Z”í Gamma: positive for “+X to +Y”

+x

+y

+z

+z'+y'

# +x

+y

+z+x'

+y

+z

+y'+x' $

+x


+x # +x+z'

%+x

Alpha > 0 Beta > 0 Gamma > 0

Example: Coordinate Rotation

# = 45 % = $ = 0

X-Y plane Y-Z plane

% = $ = 0

# = 45 % = 30$ = 0


# = 45 % = 30$ = 10

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Entity and Primitive Coordinates• Example: Cylinder subtracted

from block– Entity reference point = reference

point of the blockpoint of the block – 2 primitives:

í Block located at XYZ = 0, 0.5, 0.5; Alpha = 20

í Cylinder located at XYZ = 0, 1.7789, 4.0755; Alpha = - 7.123)

Subtract


Resulting “entity”

Entity referencepoint

Coordinates - Entity• Entity coordinates are equal to the global coordinates of

the block before the Boolean

• The entity (cube primitive + cylinder primitive) will move• The entity (cube primitive + cylinder primitive) will move together when the entity is moved

• Properties associated with the entity: – Material– Ray Traceable– Immersion


Immersion

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Coordinates – Cube Primitive• The “Absolute” coordinates of the cube primitive is

unchanged

• The “Relative” coordinates remain zero since the entity• The Relative coordinates remain zero since the entity reference point is the same as the cube primitive’s reference point


Coordinates – Cylinder Primitive• The “Absolute” coordinates of the cylinder primitive are

unchanged

Th “R l ti ” di t h h d i th• The “Relative” coordinates have changed since the reference point of the “entity” is now different


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Move Cylinder Primitive• The relative coordinates of the cylinder changed

– The new position of the cylinder is 3 units in +Z direction (global) from the entity referenceTh i t ti i 20 d ith t t th– The new orientation is 20 degrees with respect to the entity


Rotate Entity• If the entity is rotated, the

cylinder primitive will keep the same “relative” angle to the entityto t e e t ty

• The absolute position/angle of the cylinder primitive will change


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Move Cube Primitive

• If the relative position of the cube is changed, the entity will still keep its referencewill still keep its reference point

Entity moved to XYZ=0,0,0 and


the cube primitive moved to (relative) XYZ=0,-1,1

Relative Coordinates Are Important

• Relative coordinates give an excellent way to handle primitives with respect to the Boolean entityentity– No need to have any knowledge about a given

primitive’s global coordinates– Position and orientation can be specified relative to

the entity reference


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Precision Ray Trace vs. Ray Trace Acceleration• Simulations will run faster if

the geometry is set to run in Ray Trace Acceleration– The geometry is approximated

as a set of facets– Up to 100x speed improvement

• The ray trace speed will improve, but the ray trace accuracy will degrade!– The level of degradation

depends on the model


depends on the model– At the early stages of design,

the degradation may be acceptable

– For the final stages of design, use High Accuracy or Precision mode for simulations

Ray Trace Mode Is Set at the Global or Object Level


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There’s a lot more to illumination and LightTools, but this will get you started!


illumination in lighttools - the menon group · •each receiver type can have several () ¦ ¦ = =

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