Is it possible to turn off the HoloLens infrared sensors in my unity application? I am using another external infrared sensor and the HoloLens infrared lights are interfering with my other device.
That is a great question, and, so far, Microsoft has not exposed an API to turn the Infrared Lights off. From my experiments, those LEDs play two critical roles. First, they light the environment so that HoloLens can create a 3D mesh (Spatial Mapping) of the environment in a similar way to what Microsoft Kinect did in Kinect Fusion. Second, they might help with gesture recognition.
If you are not using Spatial Mapping, and most of your interaction will happen through other means then air-taps, you can safely cover those with tape. Luckily, those LEDs are not a crucial part of HoloLens' implementation of SLAM (Simultaneous Location and Mapping), so Holograms will stay anchored onto anywhere you pinned them.