5.6.5 Area Lights

The light sources discussed so far have the unrealistic feature that they cast hard shadows. Since in reality the light sources are not singular points but have some size (like the sun or a light bulb) the cast a penumbra. To model this we would have to integrate the light over that part of the light source which can be seen from a given point in space. This would be far to slow, thus the following approximate method of area lights can be used.

	light_source { S, rgb C 
	  area_light V1, V2, N1, N2 [jitter] [circular] [orient] }

This positions a $N1\times N2$-grid of point lights along the rectangle with corner $S$ and directional vectors $V1$ and $V2$ of its sides.

By using the optional keyword jitter these pointlights are randomly displaced a little to make the shadows even softer during calculation of each single pixel.

By using the optional keyword circular the rectangle is deformed to an ellipse.

Finally, the optional keyword orient takes care that the rectangle is oriented normal to each light ray it emits. This option should only be used together with circular and quadratic area lights.