There are no defined limits and this will be affected by many variables - most significantly the quality of your eyesight. Other factors include shooting distance type of weapon, caliber, optics, ammunition, size of targets and speed of target.
The dot is not projected on to the target. It is only seen inside the sight, so the distance to the target does not limit dot visibility.
In a red dot sight, the dot is not projected on to the target, it is only seen inside the sight and only by the shooter. Lasers project the reticule on to the target which makes the dot visible on the target. The red dot sight uses a LED (light emitting diode) which is completely safe for the eyes comparted to a laser that create a reticle with a laser emission, which can be harmful to your eyes.
All our sights that are compatible with NVD are designed for optimum compatibility with 3rd Generation NVDs, but they also work with 1st and 2nd generations of NVD.
Aimpoint® series sights feature either a 4 MOA dot or a 2 MOA dot.
MOA stands for "minutes of angle" and 1 MOA = 1"at 100 yards = 3 cm at 100 meters
If you have a 4 MOA, this means that the dot is about 12 cm at 100 m (4" at 100 yards), 6 cm at 50 m and 3 cm at 25m.
If you have a 2 MOA dot, this means that the dot is about 6 cm at 100m (2" at 100 yards), 3 cm at 50m and 1.5 cm at 25m