IFD Dimming setup tutorial
There are several places in the IFD that dimming control settings will affect the behavior of the backlighting and bezel lights. The 1st place to understand is in normal flight mode, accessible by the pilot, on the "Aux" > "Setup" > "Display" page, shown below.
For both "Bezel Mode" and "Display Mode" there are three options here:
1: "Photocell" - This will default the IFD dimming behavior to function as configured in the Mx Mode setup pages (explained in detail below).
2: "DimBus" - This will default the IFD dimming behavior to be driven from the aircraft dimming bus (if connected). With this setting, the IFD will ignore the ambient lighting conditions sensed by the photocell.
3: "Manual" - This setting will default the IFD dimming behavior to be driven from this page and set manually.
The next place we can affect the dimming behavior of the IFD is in Mx Mode (Main Lighting Configuration Page). The settings on this page will determine how the IFD dimming will function when the user option above is set to "Photocell" or "Dimming Bus."
You will notice that the "Configuration Parameters" above are broken into two sections. "Photo" which will determine how the photocell dimming will function, and "dimBus" which will determine how the aircraft dimming bus input will function.
"Photo Response Time" - Sets the speed at which the brightness changes when photocell is selected as the lighting source. Both the Bezel and Display fields have a range of 1 to 5, and the factory default is 3.
"Photo Slope" - The Photo Slope sets the sensitivity of the display/bezel to changes in the input when the dimming source is the IFD5XX/4XX photocell. This field has a range of 15 to 100, and the factory default is 80.
"Photo Minimum" - The Photo Minimum sets the minimum brightness when the dimming source is the photocell. Both the Bezel and Display fields have a range of 1 to 50, and the factory default is 1.
***NOTE*** If the aircraft does not have a dimming bus connected to the IFD, or if the dimming bus will not be utilized, this "minimum" should be bumped up to the 15-20 range. This will prevent certain lighting conditions causing the IFD to dim to a point of being unreadable.
"Photo Maximum" - The Photo Maximum sets the maximum brightness when the dimming source is the photocell. Both the Bezel and Display fields have a range of 50 to 100, and the factory default is 100.
***Note*** If you are not utilizing a dimming bus to control the brightness of your IFD, set the dimBus Transition % to 0 (zero). Doing so will prevent the scenario where, in increasingly darker environments (e.g. flying past sunset into dark night), the display automatically dims and dims and dims and then suddenly jumps to full bright. If you are using a dimming bus in conjunction with the Photocell, please read below the dimBus configuration descriptions and recommendations below.
"dimBus Transition %" - In installations that utilize both the photocell, as well as an aircraft dimming bus, the IFD is designed in such a way that when the "User Option Mode" described earlier in this article is set to "Auto," the IFD will use the photocell for dimming purposes down to a level that is set by this "Transition %" at which point the IFD will switch from using the photocell input to using the aircraft dimming bus input. The dimBus Transition % sets the threshold where the aircraft dimming bus takes over from the photocell. Below this threshold, the aircraft dimmer controls the IFD5XX/4XX lighting. Both the Bezel and Display fields have a range of 0 to 100, and the factory default is 10.
***Note*** If it is not desired to hand brightness control over to the dimming bus from the photocell at any point, set dimBus Transition % to 0 (zero). Doing so will prevent the scenario where, in increasingly darker environments (e.g. flying past sunset into dark night), the display automatically dims and dims and dims and then suddenly jumps to bright.
***Note*** Special attention should also be paid to this setting if the aircraft does not have a dimming bus connected to the IFD. If there is no aircraft dimming bus connected to the IFD, the IFD will sense its "dimBus" input as 0 volts. This, in conjunction with "AviCurve" being selected for the "dimBus Curve," can cause the IFD to assume that anything below this transition % will be treated like "Day Mode" and the IFD will go "Full Bright." See "dimBus Curve" below for further details.
"dimBus Slope" - The dimBus Slope sets the sensitivity of the display/bezel to the aircraft dimmer. Both the Bezel and Display fields have a range of 15 to 100, and the factory default is 60.
"dimBus Minimum" - The dimBus Minimum sets the minimum brightness when the aircraft dimmer is the dimming source. Both the Bezel and Display fields have a range of 1 to 50, and the factory default is 1.
"dimBus Maximum" - The dimBus Maximum sets the maximum brightness when the aircraft dimmer is the dimming source. Both the Bezel and Display fields have a range of 50 to 100, and the factory default is 100.
"dimBus Curve" - There are two options on this setting. AviCurve, or Proportional Curve. Each will cause the IFD to behave differently.
"AviCurve" - The AviCurve setting assumes the IFD is connected to an aircraft dimming bus that is equipped with a "Day" detent. In aircraft with a dimming bus that is equipped with a "Day" detent, turning the rheostat fully counter clockwise past the "detent" bus voltage drops below 1.5 volts (should be theoretically 0 volts). The AviCurve setting will assume this to be "Day Mode" and the IFD will go full bright.
"Proportional Curve" - The Proportional Curve tracks the aircraft lighting bus as follows: Maximum night lighting at maximum aircraft lighting bus voltage, Minimum night lighting at minimum aircraft lighting bus voltage (linear in-between).