Copyright Goodheart-Willcox Co., Inc. Chapter 18 Lighting 493 Illuminance option can be used to specify the illuminance in lux (lx) or foot-candles (fc), depending on the current lighting units. An additional option, Distance, is avail- able under Illuminance. This defaults to one unit and is used to calculate illuminance. NOTE NOTE The Shadow and Attenuation options are only available for backward compatibility with older releases of AutoCAD. Shadow casting cannot be turned off and shadow- mapped shadows are created by AutoCAD, as previously discussed. Inverse square attenuation is used regardless of the attenuation type selected. Setting the attenuation start and end limits has no effect on the scene. Target Point Lights The target point light is like a regular point light except that the command starts by asking for a source location and a target location. The rest of the options are the same. You can type TARGETPOINT or pick the Targetpoint option in the LIGHT command to create a target light. PROFESSIONAL TIP PROFESSIONAL TIP A point light may be used as an incandescent lightbulb, such as the lightbulb in a table lamp. Most of these lightbulbs cast a yellow light. In these cases, you may want to change the color of the light to a light yellow. Compact fl uorescent lightbulbs may cast white, light blue, or light yellow light. LED-based lights cast a color based on the color of the LED. Other colors can be used to give the impression of heat or colored lights. Figure 18-11. A point light is placed inside of the lamp fixture. The light projects in all directions, but the lampshade directs most of the light toward the ceiling. A full-color image is provided on the companion website. www.g-wlearning.com/CAD/ Figure 18-12. This is the light glyph for a point light.