Explanation/Reference:
Explanation:
Cisco uses a tool called a lux meter to measure the intensity of light at various points within the room.
There are essentially four different angles from which light should be measured:
From the camera's point of view, looking toward the participants

From the participant's point of view, looking toward the cameras

From the participant's point of view, facing upward toward the ceiling

From the perspective of the side and back walls

Cisco divides the room into sections, or zones, to measure light from all these different perspectives. Figure 8-27 illustrate the zones of a CTS-3000 room.

Figure 8.27 CTS-3000 illumination zones-top down view
Zones 1 to 3 provide a measure of how much light is seen from the perspective of the cameras. Zones 4 to
6 provide a measure of how much light is seen from the perspective of the participants, and hence how well lit the participants will look on camera. Zones 4 to 6 also measure how much downward light strikes the shoulders of the participants and the table surface. Zones 7 to 9 provide a measure of how much light reaches the back wall. Within each zone, it is important to note the direction from which the light should be measured. In zones 1 to 3, the measurement is taken with the lux meter facing the participants. In zones 4 to 9, the measurement is taken with the lux meter facing the cameras. In zones 4 to 6, there is an additional measurement taken with the lux meter facing up toward the ceiling at shoulder height. Figure 8-
28 illustrates the direction the lux meter should be facing within each of the zones.

Figure 8-28 CTS-3000 illumination zones-side view
In zones 1 to 3, the light is measured with the lux meter facing toward the participants at approximately 5 feet (1.5 meters) from the floor. In zones 4 to 6, two separate measurements are taken:
One with the lux meter facing toward the cameras at approximately 5 feet (1.5 meters) from the floor.

The second with the lux meter facing up toward the ceiling at approximately 4 feet (1.2 meters) from the

floor.
Finally, in zones 7 to 9, the light is measured with the lux meter facing toward the cameras at approximately 5 feet (1.5 meters) from the floor. Throughout all 9 zones, the light should measure approximately 400 lux, except for the second measurement in zones 4 to 6, in which the light should measure approximately 600 to 700 lux. No point in the room should measure lower than 150 lux or higher than 700 lux. Areas that are lower than 150 lux appear completely black on camera, and areas that are higher than 700 lux appear washed out on camera.
By following this methodology for measuring light within your TelePresence environment, you can achieve the best quality video and consistent, reproducible results. Although the illustrations provided are specific to the CTS-3000, you can use the same methodology in smaller or bigger rooms by simply shrinking or increasing the size and number of zones.
Reference: http://www.ciscopress.com/articles/article.asp?p=1351075&seqNum=3