I band

The letter I is often used an infrared passband, typically a photometric system's near-infrared (NIR) band that is closest to visible light. There are various versions of the I band: the Johnson-Cousins system has one, but I find varying specifications cited for it, one being centered around 806 nm with a width (full width at half maximum) of 149 nm. Among the I band's uses is the observation of NIR from protoplanetary disks associated with YSOs. The letter is also used to indicate the magnitude of the signal observed through the filter, e.g., citing "I = 1.5".