Chapter 17 Lighting
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If a weblight is selected, the
Photometric Web
subcategory in the
General
category
is where you can specify an IES fi le for the light. Select the
Web file
property, then pick
the browse button (…) and select the IES fi le. Once the fi le is selected, its location is
displayed in the
Web file
property. The effect of the data is shown in a graph at the
bottom of the
Photometric Web
subcategory. Refer to Figure 17-18.
The
Web offsets
subcategory allows you to rotate the web around the X, Y, and Z
axes, as discussed earlier in this chapter in the Weblight section.
In the
Geometry
category, you can change the X, Y, and Z coordinates of the light. You
can also change the X, Y, and Z coordinates of the light’s target. If the light is not targeted,
the
Target
X,
Target
Y, and
Target Z
properties are not displayed. To change the light from
targeted to free, and vice versa, select
Yes
or
No
in the
Targeted
property drop-down list.
The properties in the
Attenuation
category are the same as those discussed earlier
in this chapter in the Point Lights section. In order to change these properties in the
Properties
palette, photometric lighting must be off (LIGHTINGUNITS = 0).
The last category in the
Properties
palette is
Rendered Shadow
Details. The properties
in this category are used to control shadows. Shadows are discussed later in this chapter.
PROFESSIONAL TIP PROFESSIONAL TIP
It is important to give your lights names that make them easy to identify
in a list. If you accept the default names for lights, they will be called
Pointlight1, Spotlight5, Distantlight7, Weblight2, etc., making them diffi cult
to identify. Use the
Name
option when creating the light or, after the
light is created, the
Properties
palette to change the name of the light.
Determining Proper Light Determining Proper Light
Intensity Intensity
Placing lights usually requires adjustments to produce the results you are looking
for. In addition, you will also typically spend some time determining the proper light
intensity and other settings. As a general guideline, the object nearest to a point light
or spotlight should receive the full illumination, or full intensity, of the light. Full
intensity of any light that has an attenuation property is a value of one. Remember, as
discussed in the Attenuation section earlier in this chapter, attenuation is calculated
using the inverse linear or the inverse square method. Both methods are available
when working with standard lights. Photometric lights provide a more “real-world”
distribution of light and are set to use inverse square attenuation. Depending on the
workfl ow you are using, you can calculate the light intensity to establish an approxi-
mate starting point.
For example, suppose you have drawn an object and placed a point light and a
spotlight. The point light is 55 units from the object. The spotlight is 43 units from the
object. Use the following calculations to determine the intensity settings for the lights.
• Inverse linear. If the point light is 55 units from the object, the object receives
1/55 of the light. Therefore, set the intensity of the point light to 55 so the light
intensity striking the object has a value of 1 (55/55 = 1). Since the spotlight is 43
units from the object, set its light intensity to 43 (43/43 = 1).
• Inverse square. If the point light is 55 units from the object, the object receives
(1/55)2, or 1/3025 (552 = 3025), of the light. Therefore, set the intensity of the
point light to 3025 (3025/3025 = 1). The object receives (1/43)2, or 1/1849 (432 =
1849), of the spotlight’s illumination. Therefore, set the intensity of the spot-
light to 1849 (1849/1849 = 1).