Nikon D5500 Reference Manual page 284

A
TTL Flash Control
The following types of flash control are supported when a CPU lens is
used in combination with the built-in flash (0 93) or optional flash
units (0 323).
• i-TTL Balanced Fill-Flash for Digital SLR: Information from the 2016-pixel
RGB sensor is used to adjust flash output for a natural balance
between the main subject and the background.
• Standard i-TTL Fill-Flash for Digital SLR: Flash output is adjusted for the
main subject; the brightness of the background is not taken into
account.
Standard i-TTL flash control is used with spot metering or when
selected with the optional flash unit. i-TTL balanced fill-flash for digital
SLR is used in all other cases.
❚❚ Commander Mode
When an optional SB-500 flash unit is mounted on the accessory
shoe, select Commander mode to use the SB-500 as a master
flash controlling one or more remote optional flash units in up to
two groups (A and B) using advanced wireless lighting (0 325).
Selecting this option displays the menu
shown at right. Press 4 or 2 to highlight
the following options, 1 or 3 to change.
260 A Custom Settings: Fine-Tuning Camera Settings