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| # 3D Lights You can see the contents of a scene without lights but it everything in the scene will appear gray and flat. The settings below determine how each light will effect how the items in the scene will appear. You can have up to eight lights in each scene. ## Light Types Directional: Provides light in one direction throughout the entire scene. The light will appear to be at an infinite distance from the scene, approximating out own sun. The "Position" settings are not used for directional lights.. Positional: The light shines in all directions from a single spot. The "Direction" settings are not used for a positional light. Spot: The light appears to shine from a position in a direction into the scene. This simulates a spot light or a flashlight with the maximum illumination at the center of where the light is pointing with the light fading as it moves out from the center. ### Visible Controls if the light object can be seen in the views. Turning off this will make the light itself disappear but will not effect rendering. To "switch-off" a light without deleting it, simply change its color to black. ## Color The light's color determines the color of the light emitting from the light in the direction specified. The intensite of the color will determine the intensity of the light so bright colors are more intense while black will be no light. Middle intensity lights tend to work best as they compliment the ambient light rather than maxing out the amount of light in a scene. Ambient light should be control with the 3d view. Specular and diffuse light is controled by the definition of the material of the object. ### Position This is the position, in map units, of the source of the light. Only Poisition and Spot lights have a position. ### Direction A directional vector for the direction of Directional and Spot lights. 0,0,-1 will be pointing straight down while positive y values point the light up (north) and positive x-values point the light to the right (east). ## Visible When checked, the light will appear in the 3d and 2d views. The light can be positioned by dragging it in the 2d view. ## Attenuation This setting determines how fast the light will fade out from it's source. Small values (0.1) will make the light attenuate slower so it shows through most of the scene while large values (10) will make the light attenuate quickly, lighting only objects that are close to the light. The attenuation factors are combined to give an overall factor of: 1/(Constant+Linear*Distance+Quadratic*Distance^2) ## Spot Lights ### Cut-Off This the angle (in degrees) that the light will be cutoff to each side of the direction of the spot. 180 degrees will be no cutoff while 90 degrees will shine on each side, illuminating 1/2 the scene. 10 degrees will be a narrow light like a flashlight. ### Exponent Determines how focused the light will be in the center vs. how it trails off at the edges. 1 will give a constant light from the edge to the center while 100 will give a bright light at the center with edges that are black. # Appendix The lights in BlueSpray are limited to just one color which is set as diffuse and specular. The materials should be used to control the balance between diffusion and specular reflectance. ## LIght Colors The light colors combine with the material definitions of each object and the angle between the light and the vertex of each surface making up the object. Each color adds light coming from the object in different ways. ### Ambient Color Ambient color appears from all directions so the objects will be lighted but there will be no shading. Light added based on the ambient color of the light times the ambient color of the material. ### Specular Color Specular light simulates mirrored or shiny surfaces. This is because the light does not 'diffuse' but instead bounces off the objects in a direction based on the angle that it hits the surface. ### Diffuse Color Diffuse light is based on the angle of the light and the surface. The light is brightest where surface is perpendicular to the light. The light then 'diffuses' in all directions equally. Diffuse color is for objects that are not shiny such as paper, leather, and unfinished wood.