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Lighting

The position and nature of the light source(s) affect the appearance of solid objects such as surfaces, spheres, ribbons and cylinders. The lighting is particularly important if you are creating a ray-tracing picture using the Renderer. The same light sources are used in the Renderer but may result in noticably different effects (that's why you are using the Renderer!).

lighting

The light source can be changed from the Lighting interface which is accessed via the Display menu. By default there is one light source. Up to 8 light sources are possible. Clicking in the border with the right mouse button pops up a context menu with options including creating a new light source.

The light source can be dragged around the display by holding down the left mouse button over the lightbulb. The light source can be moved forward or back by placing the curson over the light bulb icon and holding down the Shift key and middle mouse button and dragging up or down. The size of the lightbulb icon indicates the position of the light source (large is closer to you).

A right-mouse click on a light bulb icon pops up a menu with options including Edit this light which opens a window to edit the light properties. Each light source has properties: ambient,specular and diffuse which can take values in the range 0 to 1. The effect of the different properties are probably best seen by changing the values but..
ambient light gives a completely flat, bright surface
specular light gives one bright patch on an otherwise unlit surface
diffuse light lightens all of the surface facing the light source
A combination of specular and diffuse light gives a good sense of depth and an attractive shiny surface.