> ### Setting the Light Sources

> In a typical scenario, the default light settings are often inappropriate. So let's try to recreate the better light settings as shown in the last step.
> The light sources of the scene can be modified using the Preferences dialog. Open it by clicking the menu entry
> "Edit->Preferences"
> and highlighting the entry "Lighting".

> #### Setting the Light Intensity

> Playing with the light intensity and attenuation is one of the keys to creating exciting raytracing images. Change the intensity of the current light by highlighting Light 1 in the Light Sources list and setting its intensity to 500. Activate your choice by pressing the Apply button.

> #### Set the Light Position

> A light's position can either be
> - relative to the camera or
> - absolute in the scene.
> In order to find a good light position, we attach the light to the camera, move until an acceptable scene is reached, and then change it to an absolute position.
> First attach the light relative to the camera at Position (1, -2, -15) and activate this change by pressing the Apply button.
> Then find an appropriate light position by changing the camera location (clicking and draging the mouse).
> If you found a nice spot, switch to an absolute light orientation and activate it by clicking the Apply button.
> Now we can change the camera position, e.g., rotate around the molecule, but the light will keep its position.
> Finally, try to set the light to the absolute position of (-2, 24, -14) (Do not forget to press the Apply button!) and refocus the camera (Structures window->right click->Focus).
> The resulting scene is clearly too bright. This can be changed by setting the attenuation.

> #### Change the Attenuation

> The attenuation determines the loss of intensity with increasing distance to the light source. It is determined by three coefficients:
> - constant,
> - linear, and
> - quadratic.
> Using constant attenuation, e.g., (2,0.0), the light intensity does not decrease with the distance.
> Linear attenuation, e.g., (0, 10, 0), yields a light intensity decreasing linearly with distance from the light source.
> Using quadratic attenuation, e.g. (0, 0, 1), the intensity decreases quadraticly.
> For the current scene set the attenuation to (0, 0, 0.7).
> Activate your choice by pressing the Apply button.

> #### Change the Light's Colour

> Sometimes a smoother light might look more appealing than a flashy light.
> The light's color can be changed by pressing the Edit-button of the Intensity box. Choose a smoother color, e.g., light yellow. The color can be selected using the color picker, a CMYK model, or the RGB model.
> Set a light yellow color by choosing, in the RGB-Model, Red=255, Green=245, and Blue=208.
> Activate your choice by pressing the OK button of the Select Color dialog and by pressing the Apply button.

> #### Add a Second Light Source

> More advanced light settings can be achieved by positioning additional light sources which might spice up the scene. Note, however, that raytracing performance decreases linearly with the number of light sources.
> To add a point light source, press the Add button within the Light Sources list. All its properties can be easily changed after hightlighting the new light Light 2.
> Try to position a second light source at absolute position (-6.3, 3.1; -1) with attenuation of (1, 0, 0.9), and Intensity of 18.
> Close the Preferences dialog by pressing the OK button.
> Press Next to continue.