What the image is depicting is the minimum lighting zone requirements for a presentation space (3 zones). Circuit 1 provides audience lighting (for note taking). Circuit 2 provides board lighting. The board lighting allows bright lighting for a whiteboard/chalkboard or low/off lighting levels when using projection. The presenter lighting (Circuit 3) may include task lighting and or key lighting (to highlight and provide focus on the presenter).
Provide lighting presets for different minimum contrast ratios
Going back to our earlier discussion, the challenge in presentation spaces is to strike a compromise between having enough lighting for note taking, without washing out the projection screen (which reduces the contrast ratio). Some of the lighting for students in the front of the room will inevitably bleed onto the projection screen.
The solution is to provide multiple lighting presets that provide varying compromises for different circumstances. Per ANSI/INFOCOMM 3M-2011, this means creating presets with minimum contrast ratios of 7:1, 15:1, or 50:1 to serve Passive Viewing, Basic Decision Making, and Analytical Decision Making, respectively. This is just a fancy way of saying that we need presets for different compromises between image quality and lighting levels for note taking.