C182 instructor reports that G1000 MFD/PFD brightness control knob functions opposite to that indicated by graphic printed around the knob.

Narrative

Planned local orientation flight in a 2007 Cessna 182T Nav III. During ground OPS with 2 students on board; had very dark/dim PFD and MFD screens. Pilot elected to cancel the flight. Students were released and 2 other Pilots joined him (one a CFI/CFII) in checking out the system; especially to see if pilot system error had caused the unreadable screens. Subsequent adjustment of dimmer panel avionics rheostat showed normal screen operation. The 3 Pilots briefed multiple possible malfunction scenarios (communication/transponder; loss of PFD information; etc) and elected to complete a short pattern-only flight to confirm normal system operation. Contacted Tower for a 'maintenance test' pattern-only flight; flew 2 normal patterns and landings. All systems on the aircraft (including transponder and communication/navigation radios) were fully functional before; during; and after start; and throughout the flight. Subsequent review of Avionics dimmer rheostat operation (panel markings and Section 7 of the AFM) indicates improper markings and confusing explanation of how PFD/MFD screen dimming actually functions. Rheostat marking indicates brightness increases as the rheostat is turned clockwise from the off (automatic photocell) position; and AFM Section 7 does not clarify actual operation. Our ground test indicates the screens actually go dim and eventually unreadable as rheostat is rotated clockwise. We are trying to confirm this dimmer rheostat operation/anomaly with Cessna Airplane Company. Callback conversation with Reporter revealed the following information: The reporter states that the manufacturer plans to fix this problem with software and that the knob in question works fine; only not according to the graphic around the knob.