| Light Ray: To place a light ray, click on a light source, then drag out the ray in the direction and to the length you desire. To move the light ray along the light source (other than a point source), select the ray and drag it vertically along the source. You can also use the up and down arrow keys to move the ray one pixel at a time. To extend or contract a ray and change its direction, select the ray. Then click on the "hot spot" on the arrowhead and drag the ray to the desired length and direction. Light rays only follow actual light paths in Run mode. In a ray's Properties Box, you can change the ray's color. You can also choose to show the backward extension of refracted rays . This option shows the apparent location of the light source to observers. The backward extensions are gray and colinear with the refracted rays. You can choose to show backward extensions at only the last refracting surface or all refracting surfaces encountered by the ray.