Tuesday, July 26, 2011

The ABC's of NVD's

Limitations to keep in mind when players decide to use Night Vision Devices. This article taken directly from the US Army's 'Countermeasure' magazine April 2003 issue.

Hope it helps a few GMs out there.


Wow! A soldier has just looked through night vision goggles (NVGs) for the first time. He can see – he thinks – and he'd like to put the goggles on and go. What he doesn't know is that while NVGs increase night light to incredible levels, they don't turn night into day and they don't show him everything. Like all Night Vision Devices (NVDs), the goggles have some limitations. Some of those are limitations in the devices themselves while others are in the eye. Sometimes those limitations show up in the accident reports and they're worth being aware of. Let's look at some of the most common concerns.

Reduced Field of View
The view through NVDs can be a lot like looking down a tunnel. Your normal field of view is almost 190 degrees – but that is cut down to 40 degrees with NVDs. That side – or "peripheral" – vision you're accustomed to, and from which you often see your dangers, is just not there. To adjust for that you must constantly turn your head to scan for the dangers on either side of you that you can's see in your narrow field of view.

Reduced Visual Acuity (Sharpness)
At their best, NVGs cannot provide the same level of sharpness to what you see as what you're accustomed to in the daytime. While normal vision is 20/20, NVGs can, at best, provide only 20/25 to 20/40, and even this is possible only during optimal illumination and when you have a high-contrast target or scene. As either illumination or contrast decreases, the NVGs visual acuity drops, giving you an even more "fuzzy" image.

Reduced Depth and Distance Perception
Normally you use both eyes (binocular vision) to pick up the cues to help estimate the distance and depth of an object. However, with NVDs you are essentially using one eye (monocular) vision, which can pose real problems. For example, when you are wearing NVDs and you view two objects of different sizes that are side-by-side, the larger object appears to be nearer. When you view overlapping objects through an NVD, the one that is in front "appears" to be nearer – maybe much more so than is true. In addition, some objects viewed through NVGs may appear to be farther away than they actually are. The reason for that is that we tend to associate the loss of detail sharpness with distance. On the other hand, a light source that is not part of a terrain feature – for example, a light atop a tower – may look closer than it actually is. It's important to be aware of these potential problems and that NVG users tend to overestimate distance and underestimate the depth (how tall an object is).

Dark Adaptation
Your eye needs time to adjust from day to night vision. That's why you can barely see when you first enter a dark movie theater during the daytime – your eyes need time to adjust to the darkness. So it is with NVGs. You are basically getting a dim-day view, so when you remove your NVGs, your eyes need time to adapt to the darkness. The amount of time you need depends on how long you have been wearing the NVGs. Most people achieve about a 75 percent dark-adaptation within 30 seconds of removing the goggles. This is especially important to keep in mind if you are using your NVGs as binoculars – basically lifting them to your eyes and lowering them.

In Summary
Accidents ranging from fender-benders to mission stoppers sometimes happen because people misinterpret what they see through their NVDs. To train safely and win on the battlefield, you need to understand the limitations of your night vision equipment and be skilled in using it. Leaders also need to be aware of the hazards involved in NVD operations and take measures to control the risks.

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