What Is A Spot Chart? Night Vision Experts Provide Answers

October 24, 2022

Image intensifier tube clarity is vital to those using night vision goggles or other devices, particularly if you use them with weapons. Black spots can appear in the image intensifiers, and a spot zone chart test shows spot size and location.

What Is Night Vision?

Good night vision equipment uses infrared technology and starlight or other sources of ambient light and illumination, even in near darkness, to produce a bright and clear green or white image, making fine details visible in low-light levels.

Users recognize a noticeable improvement in the ability to see shape detail and distinguish objects from the background, even those in the distance. When compared to the naked eye, night vision images are illuminated better, providing contrast and a crisp appearance.

A dark spot doesn’t affect the performance of the glasses, but Steele Industries recommends testing the image intensifier tubes for spots and blemishes using a standard spot chart. Blurred or distorted vision may affect your ability to use the devices.

What Does a Spot Chart Look Like?

Picture an image with three circles inside each other. The circle in the center is zone one, with zones two and three surrounding it.

During a test, the technician takes a photo of the image produced by an intensifier tube focused on the spot chart. Manufacturers reject tubes if they note:

  • Too many dark spots per zone
  • Large spot size
  • A cluster of spots

To be considered a spot, the size must meet or exceed .003″ in diameter.

What Are Spot Spec Tolerances?

Spot spec tolerances may differ by manufacturer and vary for commercial, military, and aviation uses:

  • Commercial: maximum of four, with a zone one spot allowed.
  • Military standard: maximum of four; however, none in zone one and no more than three in zone two, with three spots max per tube.
  • Aviation: maximum of three per tube, with none in zones one or two.

After testing, manufacturers typically keep the tube images and spot detail with the correlating spec sheet.

Are Spots the Same as Blemishes?

Blemishes are user produced and can include streaks, debris, splotches, shades, and burns. Prolonged exposure to bright lights or a static image can produce temporary or permanent burns.

Dark spots result from manufacturing processes and are permanent. Sometimes, a particle can become wedged in the fiber optics or intensifier.

How Can You Protect Your Night Vision Equipment?

Daylight, brighter lights, and prolonged exposure to light can damage sensitive image intensifier tubes. If you’re wondering how to protect your equipment:

  • Turn the unit off when a person isn’t using it.
  • Don’t aim directly at light or reflective surfaces.
  • Don’t use it if you’ve noticed a big difference in environmental conditions and light sources.
  • Black box the unit to let the tubes rest before powering off if you notice a burn or other blemish.

How Can Steele Industries Help?

As a recognized leader, Steele Industries intimately understands night vision. They can explain how different components function, help you determine the cause if something appears to be wrong with your equipment and suggest ways to fix or replace it.

Steele Industries’ lead time is shorter than most suppliers. If you need parts or new equipment, you won’t need to wait long.