Basic Principles of Red Dot Sights Operation

Chris G.

When shooting a firearm, a shooter generally uses the firearm’s iron sights to align and hopefully hit a target. Using this method of sighting is effective, but it has several drawbacks. The shooter needs to allocate time, effort, and precision to align the front and rear sights. In dynamic situations such as competitive shooting, obstacle shooting, or law enforcement operations, this could be disadvantageous.

Enter the red dot. This optic ingeniously solves the challenge of balancing precision with speed. This device uses light reflection, refraction, and collimation principles to produce a bright red dot as a reference point to mark the target. 

This article provides a brief but thorough explanation of how red dot sights work.

How Do Red Dot Sights Work?

a diagram of how a red dot works

A red dot sight utilizes a blend of LED light, specially coated lenses, and reflective technology to project a red reticle—often in the form of a dot—onto a lens. This red dot serves as a point of aim, allowing users to quickly and accurately target objects. It works on a simple principle.

The optic contains a solid-state LED (Light Emitting Diode) that emits a small, focused beam of red light. Sometimes, the light is of some other color such as green. 

The lens on the sight is specially coated with a silvered multi-layer dielectric dichroic coating to reflect only the red spectrum through the glass while allowing other wavelengths to pass through. This coating ensures only the red light is visible to the user, creating the characteristic red dot.

Technically, this red dot is called a reticle.  There are variations such as circle-dot or crosshair designs; it depends on the aperture of the emitter.  In some models, the size and shape of the reticle can be adjusted. Red dot sights usually come with adjustable brightness settings—whether automatic or manual or both—to ensure the reticle is visible in different lighting conditions.

A modern red dot sights are designed to be parallax-free at infinity using the principle of collimation. This means that the red dot will stay on the target regardless of the position of the user’s eye. 

Red dot sights are powered by batteries, and some models may also feature solar panels for additional power or as a backup. 

When using the red dot for the first time, a shooter needs to zero the dot sight. This means aligning the point of impact with the reticle at an optimum distance. This involves adjusting windage (horizontal) and elevation (vertical) settings to match the bullet’s point of impact at a specified distance.

Key Features and Components of Red Dot Sights

Like many electronic devices, red dots are made of several components working in sync with one another. While the quality, design, style, and other factors differ, most red dots share the same general components.

  1. Objective Lens: The front lens that allows light to enter the sight. It gathers and transmits ambient light to the internal components.
  2. Coated Lens: Specially coated to enhance light transmission, reduce glare, and improve image clarity. These coats also ensure the projection of a clear and bright reticle.
  3. Spherical Mirror: Reflects or refracts light to create the illuminated reticle.
  4. LED (Light Emitting Diode): Emits light of a specific wavelength to create the reticle. The light generated by the diode is projected to the lens.
  5. Reticle: The aiming point visible to the shooter. It provides a reference point for aligning the firearm with the target. It can be a simple dot, circle-dot, crosshair, or other pattern, depending on the sight model.
  6. Adjustment Turrets: Windage and elevation adjustment controls. Adjusting these controls allows users to zero the sight.
  7. Brightness Control: Adjusts the intensity of the illuminated reticle. Shooters can adjust the reticle brightness to make it visible in certain lighting conditions.
  8. Power Source: Provides electrical power to the LED. Typically, these are batteries (commonly CR2032).
  9. Housing: Encases and protects the internal components. These are usually made of light and durable materials like aluminum or polymer. Housings are sealed or nitrogen-purged to prevent moisture from seeping in. They are designed to either absorb or deflect impacts, vibrations, and recoils.
  10. Mounting System: Attaches the sight to the firearm. These include risers, weaver/picatinny rails, quick-detach mounts, or specific mounts designed for particular firearms.

Different Types of Red Dot Sights

an image of different red dot sight

The firearms optic industry offers a wide variety of red dot sights that cater to different shooting needs and weapon platforms. 

  1. Tube-style Red Dot Sights
    • Design: Resembles a small, tube-shaped optic
    • Reticle: Typically a simple dot, though some models may offer additional reticle options
    • Applications: Common on rifles and shotguns
    • Examples: Aimpoint PRO (Patrol Rifle Optic), Vortex Crossfire, Trijicon MRO (Miniature Rifle Optic)
  2. Reflex-style Red Dot Sights
    • Design: Open or tubeless design with a single lens
    • Reticle: Projected onto the lens, usually a simple dot or circle-dot
    • Applications: Versatile, used on handguns, shotguns, and rifles
    • Examples: Trijicon RMR (Ruggedized Miniature Reflex), Leupold DeltaPoint Pro, EOTech EXPS series
  3. Miniature Red Dot Sights (MRDS)
    • Design: Extremely compact and lightweight
    • Reticle: Typically a simple dot
    • Applications: Often mounted on handguns, shotguns, or as secondary optics on rifles
    • Examples: Trijicon RMR (Ruggedized Miniature Reflex), Leupold DeltaPoint Micro
  4. Holographic Sights
    • Design: Use holographic technology to project a reticle onto a lens
    • Reticle: Offers a more complex reticle design with a wide field of view
    • Applications: Common on rifles and submachine guns
    • Examples: EOTech Holographic Weapon Sight (EXPS series), Vortex AMG UH-1
  5. Prismatic Sights
    • Design: Compact with a prism-based system
    • Reticle: Etched onto a prism, allowing for an etched reticle in addition to illumination
    • Applications: Suitable for various firearms
    • Examples: Trijicon ACOG (Advanced Combat Optical Gunsight), Primary Arms SLx Compact Prism Scope

Conclusion

Red dot sights are a valuable addition to any shooter’s arsenal. These optics allow shooters to quickly acquire and lock targets without much difficulty. These optics function using the clever combined use of LED projection and a concave lens and using the principles of reflection and collimation.

There’s a variety of red dot optics available. These sights provide a seamless transition from traditional iron sights to fixed-power optics.

While they do have a few minor limitations, their adaptability and user-friendly nature have made them a popular choice in the world of firearm optics.

About the author

The name's Chris. Just a regular dude who loves firearms. I've been shooting since I was a kid. My old man taught me the ropes.

I'll never forget the first time I missed an easy shot on a buck, thanks to a bum scope. The image was fuzzier than my dog's butt. After that, I got obsessed with understanding scopes. What makes the good ones tick and the bad ones trash. After a few years and a few thousand bucks, I learned what separates the winners from the losers. Once I had a good stockpile of knowledge, I launched this site.

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