Copyright Goodheart-Willcox Co., Inc. Chapter 18 Lighting 499 applied to the color of the light. The Resulting color: swatch displays the color cast by the light once the fi lter color is applied. If the fi lter color is white (255,255,255), then the light color is the color cast by the light. 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 button to the right 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 18-17. 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 for lights that have attenuation properties. The Type property is set to Inverse Square and is read-only. The attenuation limits properties are read-only and are only for back- ward compatibility with older releases of AutoCAD. 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 earlier in this chapter, AutoCAD calculates attenuation using the inverse square method. You can calculate the light intensity based on this method to establish an approximate 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 based on inverse square attenuation. Since 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). Since the spotlight is 43 units from the object, the object receives (1/43)2, or 1/1849 (432 = 1849), of the spotlight’s illumination. Therefore, set the intensity of the spotlight to 1849 (1849/1849 = 1). However, keep in mind that these settings are merely a starting point. You will likely spend some time adjusting lighting to produce the desired results. In some cases, it may take longer to light the scene than it did to model it.