|Adding Sunlight to your Drawings
Once you start working with
solid models and rendering them, you will want to add lighting
effects to your model. One of the most common requirements is
to add sunlight to your drawing. AutoCAD has some very
powerful and useful features for accurately creating sunlight
As you may have realised by
now, you don't need lights in a scene in order to render a
model. Figure number 1 on the left shows the effect of
rendering without lights. As you can see, the results are
rather uninspiring and there are no shadows. AutoCAD
calculates the lighting in a scene where there are no lights
by determining the the angle of incidence between the object
faces and the line of sight. Faces that are perpendicular or
near perpendicular to the line of sight are displayed brighter
and faces further from the perpendicular are shown darker. The
effect is similar to what you would see if the light source
was placed at the camera position; perpendicular faces would
reflect more light and faces further from the perpendicular
would reflect less light. In figure 1, you can see that the
vertical faces of the hedge, facing the viewer are bright,
whereas the ground plane is quite dark. Although this effect
enables you to clearly see your model, it is far from
In order to add some sunlight to our scene, we will need to
add a light that simulates the sun; AutoCAD calls this type of
light a "Distant Light". This is much easier than it sounds
and AutoCAD has some very user-friendly tools to help.
As you can see from figures 2, 3 and 4, not only can you
simulate sunlight but you can control the time of day, the day
of the year and the geographic location. Also, because the
renderer can create accurate shadows based upon your
parameters, you could even use these techniques to create a
The three sunlight images on the left show the light and
shadow effects on a garden at different times of the day on
the 25th June in London. This is all possible without needing
to know the first thing about solar geometry!
This tutorial will take you, step-by-step through the
process of creating sunlight, modifying it and making the
necessary shadow and render settings.
Overview & Fast Track
sunlight and rendering a drawing is essentially a 5 step
process. If you are familiar with AutoCAD, you may be able to
create sunlight by following the Fast Track steps below. If
you have never worked with lights before or have never used
the renderer, I suggest you follow the full tutorial. Start by
downloading the Sample
Data or go straight to Getting
a Distant Light using the Light command, ViewRenderLight… from the pull-down menu.
Set the light type to "Distant Light" and click the New…
the light and set Shadow Type to "Raytraced" in the New
Distant Light dialogue box. Give the new light a name. Click
the checkbox to turn shadows on and then click the Shadow
Options… button. Click the checkbox to turn "Ray Traced
the Time using the Sun Angle Calculator. Click the Sun
Angle Calculator… button in the New Distant Light dialogue
the Location from the Sun Angle Calculator dialogue box.
Click the Geographic Location… button in the Sun Angle
Calculator dialogue box.
the Scene using the Render command, ViewRenderRender… from the pull-down
menu. Set the "Rendering Type" to Photo Raytrace and click
the checkbox to turn "Shadows" on.
Download Sample Data
You can use any 3D
drawing to follow this tutorial providing that you have drawn
a ground plane on which the shadows can be projected.
Alternatively, you can download the file shown in the images
above. Click on the icon below to download the AutoCAD drawing
file Garden.dwg. There are two download options, you
can either download the drawing file or you can download the
smaller compressed file. The compressed Zip file can be
uncompressed with a utility such as WinZip.
(367KB) - AutoCAD 2000 Drawing FileSave the file to the
folder where you keep your AutoCAD drawing files. If you
downloaded the zipped version, you will need to unzip it
(73KB) - AutoCAD File Zipped
Open the Garden.dwg
file. You may notice that it is a little slow to open. This is
because the garden is constructed from solid objects and
AutoCAD has to load some extra bits of the program to deal
with them. The opening view is an aerial perspective. This was
created using the DVIEW
command but you could also use 3D Orbit. The view has been
saved so that you can return to it at any time using the Named
Views command, from the Standard toolbar or
ViewNamed Views…. Highlight the view
name, "Sun View", click the "Set Current" button and then
In addition to the saved view,
the garden drawing also has the various render settings
already saved for you. However, if you are not familiar with
rendering, it would be useful to have a quick go now so that
you know what to expect later in the tutorial.
After opening the Garden.dwg, select ViewRenderRender… from the pull-down menu
or click on the render toolbar to display the
Render dialogue box. Since all of the settings are already
made, simply click the OK button. After a few moments, the
rendered image will appear in your viewport and your screen
should look something like the image above. Notice that the
render background has been set to white. This just makes the
rendered objects easier to see. Notice also that some of the
objects have materials assigned.
Note that rendered views are not interactive, they are just
still images, like photographs. You cannot pan, zoom or pick
objects in a rendered view as you can in shaded views.
Therefore, you must return to your previous viewing mode
before continuing with any drawing work. To do this, you must
regenerate the view, select ViewRegen from the pull-down menu.
The rendered image that you see is shown with the default
lighting as described above and illustrated in figure 1. We
have not yet added any lights, so this is the next thing to
Adding a Light
The first step
toward simulating sunlight is to create a new "Distant Light".
AutoCAD can create 3 different types of light, namely,
Point Light, Spotlight and Distant Light. It is important to
understand how each of these light types affects the final
rendered image. A point light radiates light in all directions
from a single point. A real-world example of this type of
light is the bulb of a ceiling pendant light. A spotlight
creates a conical light that is also directional. This is
similar to a real-world spotlight. Distant lights differ from
both point lights and spotlights in that their light rays are
not radial, they are parallel.
Why are distant lights used to simulate sunlight? Well,
although light rays from the Sun are radial, we are so far
away from the Sun that the angle between light rays is very
small by the time they reach the Earth. To all intents and
purposes, they are parallel and since light rays from distant
lights are parallel, they most closely resemble sunlight.
So, to create a new distant light, select ViewRenderLight… from the pull-down menu.
When the Lights dialogue box appears, select "Distant Light"
from the drop-down list and then click the New… button. This
will take you to the New Distant Light dialogue box.
Configuring a Distant Light
step to simulating sunlight is to name the light and to set
the shadow options.
Click in the "Light Name" edit box and type the name of
your new distant light. For the sake of simplicity, it might
be sensible to call the light "SUN". However, you can call it
anything you like providing that it is eight characters or
less and doesn't include any of the normal illegal characters
such as spaces, asterisks, slashes and dots. If the light name
you choose is not liked by AutoCAD, you will see a small error
message in the lower left-hand corner of the dialogue box
saying "Invalid name".
Setting shadow options for a light involves turning shadows
on and then specifying the shadow type. When you create any
light, you can decide whether it will cast shadows or not. In
some cases it is desirable that lights do not cast shadows.
This ability to control shadow casting means that you could
build a scene with a number of lights, some of which cast
shadows and some of which don't. To turn shadows on, click in
the "Shadow On" checkbox (shadows are turned off by default).
Now you can set the shadow type. Click the Shadow Options…
button to display the Shadow Options dialogue box.
Setting Shadow Options
renderer can create three different types of shadows. The
default shadow type is "Shadow Map" and the alternatives are
"Volumetric" and "Ray Traced". You can see from the
illustrations below that the shadow map and ray traced shadow
types give quite different results. For most objects, the
difference between Volumetric and Ray Traced shadows is very
small. See All
about Shadows for a full description of these shadow
types. The type of shadow you use is entirely up to you but in
general, ray traced shadows tend to give a better result.
The Shadow Options dialogue box is used
to specify which shadow type is used when you render the
scene. The default shadow type is the shadow map.
Click the "Shadow Volumes/Ray Traced Shadows" check box to
change the shadow type. Your dialogue box should now look like
the one on the right. Click the OK button to return to the New
Distant Light dialogue box.
Using the Sun Angle Calculator
step in simulating sunlight is to set the date and time using
the Sun Angle Calculator. From the New Distant Light dialogue
box, click the Sun Angle Calculator… button to display the Sun
Angle Calculator dialogue box.
In order to set the date and time, you must specify the
date, the time, the time zone and decide whether you want
daylight savings or not.
Starting at the top of the left-hand column in the dialogue
box, click in the "Date" edit box and type the date. Note that
dates are in the American format (mm/dd). Next, click in the
"Clock Time" edit box and enter the time. Note that this is in
24 hour format or military time. If you wish, you can use the
adjacent slider bars to set the date and time but it is very
difficult to control accurately and is therefore not
Using the drop-down list, select the required time zone.
For example, if your site is in the UK, select the "GMT/WET"
option. Finally, you need to decide whether you would like
daylight savings to be calculated. This option will
automatically convert GMT (Greenwich Mean Time) to BST
(British Summer Time). Most likely you will want to have this
option turned on, so click the "Daylight Savings" checkbox.
You will notice that AutoCAD allows you to specify the
latitude and longitude of your site. These values must be
known in order for AutoCAD to accurately calculate the angle
of the Sun. In most cases you won't know these values but
fortunately, AutoCAD can help us to locate our site
Geographically. Click the Geographic Location… button.
Setting the Geographic Location
fourth step in simulating sunlight is to specify the
geographic location of your site. The Geographic Location
dialogue box enables you to do this in a number of ways.
The first thing to do is to specify which continent your
site is in. Use the drop-down list, centre top of the dialogue
box, to select a continent. Once you have done this, you have
a number of options. You can simply select the name of a city
from the list on the left. You can also select a city by
checking the "Nearest Big City" option and picking a point on
the map. If your site is not near a big city, you can deselect
this option and simply pick any point on the map. Obviously it
is very difficult to accurately pick a location from such a
small map but you should be able to get close enough to
generate realistic shadows.
You have now made all the settings that are needed to
simulate sunlight. Click the OK button to return to the Sun
Angle Calculator dialogue box. Click the OK button again to
return to the New Distant Light dialogue box, click OK a third
time to return to the Lights dialogue box and finally, click
OK one more time to complete the specification for your
This might be a good time to save your drawing if you
haven't already done so.
Rendering the Scene
The fifth and final
step to simulating sunlight is to render a view of your
drawing in order to show the effects of light and shadow.
Start the Render command by selecting ViewRenderRender… from the pull-down menu.
The Render dialogue box will appear. First, make sure that the
Rendering Type option is set to "Photo Raytrace". Next, make
sure that "Shadows" is checked in the Rendering Options
section of the dialogue box. Shadows will not be generated if
this option is not checked, even if shadows are turned on for
If you are not using the Garden sample drawing, you should
also check that the Destination is set to "Viewport". You may
also like to set the render background colour to white.
When you are sure that all settings have been made
correctly (your dialogue box should look similar to the one
illustrated above), click the Render button. AutoCAD will take
a few seconds to render the scene (times will vary depending
upon the complexity of the scene and the speed of your
Modifying Sun Light
Once you have
created your first sunlight render, you may want to change the
time of day or date of the year in order to demonstrate the
changing effect of sunlight on your site. You can modify your
distant light settings at any time. To do so, select
ViewRenderLight… from the pull-down menu to
go to the Lights dialogue box. Select your light from the list
on the left of the dialogue box and click the Modify… button.
This will take you to the Modify Distant Light dialogue box.
From here you can modify any of the settings you made when
you first configured the light. When your changes have been
made, render the scene again and you will see the results of
your modification. You could use this technique to create
images of your site at hourly intervals during a single day or
at the same time of day at different times of the year. This
will give a good idea how sunlight will affect your site at
Tips & Tricks
- You may notice that when you create a
light for the first time in a drawing, you not only gain a
light but you also gain a small icon representing the light
and a special new layer. Distant lights are displayed using
the icon shown on the right and the name of the light is
also shown. Do not move or erase distant light icons.
Erasing the icon will delete the light. The new layer
created for the light icon is called "ASHADE" and it is a
special AutoCAD layer. Do not use this layer for anything
else. However, if you would like
to hide your light icons, turn this layer off or freeze it.
- To save your rendered images to file, set the
Destination in the Render dialogue box to "File" and then
use the More Options… button to configure file output.
- Remember that shadows are only visible if they are cast
against some solid object. For example, if you want to see
shadows cast on the ground, you will need to draw a ground
- Working with shadow mapped shadows can be tricky and
AutoCAD can sometimes throw up unexpected results. Use
raytraced shadows to avoid confusion. See the All
about Shadows tutorial for more details.