The collimator is designed to be used in all light conditions. To use it during low light conditions, or with an image intensified night vision sight, an included LED Illumination Module is used to backlight the collimator grid.
In order to use the SAC in low light or dark conditions, simply unscrew the LED light source from its storage position and screw it into the back of the optical tube (located just above the storage position). This provides background illumination so that the SAC grid can be seen through image intensified night vision sights or optical sights. Note that the LED module will not illuminate until it is properly seated behind the optical tube. This prevents accidental discharges of light that could give the shooters position away to enemy forces.
A small flashlight (or IR light source for NV sights) can also be used to backlight the collimator grid if the attached light source becomes lost or inoperable.