With the new version of the photo/video plug-in , there are 2 ways to have an automatic light.
- Use the automatic light sphere available in the libraries provided
- Use the [font=times new roman]automatic[/font] and [font=times new roman]SphereLight[/font] keywords in the description property of the light you create

Just enter the light power and the light source manager will do the rest when you change the time.