Autodesk 12812-051462-9011 User Guide 3 - Page 1487

Physical Scale Sets a physical scale for exposure control to use with lights that are not physically based. The result is an adjustment of the rendering that approximates the eye's response to the scene. Each standard light's Multiplier on page 8055 is multiplied by the Physical Scale value to give a light intensity value in candelas. For example, with the default Physical Scale of 1500, a standard omni light is treated by the renderer and radiosity as a photometric isotropic light of 1500 candelas. Physical Scale is also factored into reflections, refractions, and self-illumination. TIP You need to set the Physical Scale when you use ray-tracing with self illumination. Set this value to the equivalent of the brightest light source in the scene. This will set the appropriate conversion scale for reflections, self-illumination, and all other non-physically based elements a material offers. In some cases, an object might reflect or emit more light than the brightest light object in the scene; in this case, use the object's Luminance value as the Physical Scale. NOTE The mental ray renderer treats Physical Scale in the same way the scanline renderer does in terms of its effect on reflections and refractions. Physical Scale does affect the appearance of self-illuminated materials. Range=0.0 to 200,000.0 candelas. Default=1500.0. A single candle is approximately 1 candela (the unit can also be called a "candle"). A 100-Watt (W) incandescent light bulb is approximately 139 candelas (cd). A 60W bulb emitting in all directions is about 70 cd, while the same bulb with a reflector is about 4500 cd because the light flux is concentrated into a narrow angle. Photometric lights are unaffected by the Physical Scale value. This parameter is animatable. Color Correction check box and color swatch When the check box is turned on, color correction shifts all colors so the color displayed in the color swatch appears as white. Default=off. Clicking the color swatch displays a Color Selector on page 391 so you can choose the color to adapt to. You can use this control to simulate how the eye adjusts to lighting. For example, even when the light in a room has a yellow hue from an incandescent light bulb, we will continue to perceive objects that we know to be white, such as printed pages, as white. TIP For the best results, use a very pale color correction color, such as a pale blue or pale yellow. 6742 | Chapter 21 Effects and Environments