One of the innovations implemented in new Maya 2008 is the portal light. The portallight is used in interior lighting, is a shader that connects to a area light for channeling rays of the phisical sun + sky that are lost in our interior scene to go to better illuminate areas not exposed to direct sunlight or skylight. Use the mia_portal_light shader to create a portal light to reduce final gather rays and rendering times.

1 create area light
2 enable Area shape in the mental ray section
3 add th protal for both the light emmiter and phtons