Red dot sights, also referred to as reflex sights, are a typical package offering with several crossbow manufacturers.
They are reliable and effective and many shooters prefer this sight system in lieu of a magnified scope. They are compact and also available in multi-dot configurations, which act as drop compensators, working the same as the multiple crosshair scope. Additionally, they can include low power magnification, which considerably enhances their effectiveness.
Like the holographic sight, it has become very popular with military and law enforcement personnel due to its quick target acquisition ability on both static and moving targets.
Differing from the holographic sight, the aiming reticle, or dot, is projected forward from a point behind the objective lens. It is then reflected off the back of the objective lens back toward the shooter. The objective lens, in effect, acts as a mirror.
This condition means that the lens will not allow as much light to pass through it as a regular lens, such as a scope lens. The lens is typically coated with compounds that allow only the lights color (the dot) to be blocked, thus reflecting back, and allows all other colors of the spectrum to pass through.
It should be noted that a red dot sight is not a laser by any definition, and does not project any image toward or onto the target. Red dot sights are sighted in following the same principles as magnified scopes.