How Do NVDs Work and What Color Is The Best For Aviation Night Vision?

A 2 goggle night vision for soldiers

Many pilots find night flying enjoyable. Under night VFR conditions, the air tends to be smoother, airports with beacons are easy to find, there is generally less traffic, and other aircraft can be easier to see because of the use of anti-collision beacons and strobe lights.

You may be wondering how they could see during night flights. This is where Night Vision Devices prove to be useful. But what are NVDs? What color is the best for aviation night vision? In this article, we will answer your questions as we look deeper into Night Vision Devices.

How Does Night Vision Work

A night vision device (NVD) amplifies available light so you can see in dark or lowlight conditions. Although technology has evolved dramatically since its introduction in the 1930s, the basic premise remains the same.

An NVD functions by directing light to an objective lens. The lens then focuses on an image intensifier device. Then, a photocathode transforms light into energy and directs it onto a screen to produce an image.

Today, there are various NVDs, including night vision scopes, monoculars, binoculars, and goggles. Moreover, there are two types of night vision images: traditional monochrome green and digital color.

What Color Is The Best for Aviation Night Vision?

Why Is It Green?

What color is the best for aviation night vision?

There are two main technologies used in the development of night vision. The first type is active illumination technology, couples imaging intensification with an illumination source in the near-infrared band.

The other technology, image intensification, answers why night vision is green. Image intensification technology gives us that famous bright green light in night vision goggles.

If this sounds complicated and confusing, it’s time to dive into the essence of visualizing objects hidden by the night’s darkness. We are talking about darkness, as the device will become useless if you use it in a blizzard, fog, or even heavy rain. Science has various solutions for these conditions.

But what makes the synergy of sophisticated equipment in a night vision device? It boosts the amount of light received from natural sources such as moonlight and starlight and “amplifies” it in night vision devices to create a clear image. Regrettably, this means that night vision goggles with this technology can’t operate in complete darkness since it doesn’t amplify the light. Instead, it illuminates it to a level where the human eye can detect it.

Once photons hit the lens at the front of night vision goggles, they still carry the light of all colors. However, they lose that data once transformed into electrons, and the arriving color light transforms into grayscale. But why is night vision green, then?

The primary reason is that the image intensification screen inside the device comprises a phosphor. This substance is used due to its luminance effect, and once struck by electrons that do not carry color information, it glows bright green. During the time the electrons pass through the tube, they move through a microchannel plate, a disc that includes millions of microchannels.

Striking these microchannels with voltage bursts causes the motion to increase quickly, forming dense clouds of electrons that enhance the original image. These electrons then strike a screen coated with / phosphor at the end of the tube. The energy from these electrons creates a greenish image on the screen inside the device. Green phosphor is utilized since the human eye is most sensitive to the color green pallet and differentiates more shades of green than any other color.

How About White?

Some intensifier tubes also form black and white images

Most intensifier tubes produce green images because human vision can differentiate between many more shades of green than any other color. This enhances object or target recognition in tactical applications and security surveillance.

However, tubes with White Phosphor technology are also available for operators who prefer black-and-white images. Both 2nd- and 3rd-generation products are available with the white phosphor option.

4 Generations of Night Vision Technology

One of the most common questions about night vision technology is, “What’s the difference between night vision generations?”

While all NVDs function using similar technology, the quality of the image is determined by the acceleration of electrons. The key difference between night vision generations is the intensifier technology.

Generation 0

Generation 0 is the oldest image intensifier technology, dating to the German army’s first military use during World War II. The operation concept was inspired by the RCA Corporation’s image-converter tubes, developed in the mid-1930s for television use. 0 generation photocathodes, called S-1 cathodes (AgOCs), had very low efficiency, low gain, and short range, and produced very dim images on the phosphor screen. To be useful, 0-generation tubes needed powerful external infrared lamps to illuminate the scene.  ​

Since then, this type of night vision evolved from generation 0 to generation 3, improving sensitivity, resolution, image clarity, brightness, and color. However, the main concept of operation remains the same: conversion of reflected ambient infrared light into visible light. Generation 0 technology is considered obsolete and not in production nowadays. ​

Generation 1

To improve sensitivity, gain, image brightness, and to reduce reliance on large infrared lamps, a new 1st-generation multi-alkali photocathode design (employing a sodium-potassium-antimony-cesium “Na-K-Sb-Cs” formula, commonly referred to as an S-20), connecting three intensifier tubes in series, was introduced in the early 1960s. It proved successful in significantly improving sensitivity, gain, and image brightness but made night-vision devices larger and heavier.

Generation 2

The 2nd-generation night vision technology was born around the late 1960s with micro-channel plates (MCP) inside the intensifier tubes. MCPs amplify the number of electrons reaching the phosphor screen thousands of times, increasing the device’s gain.

Another significant improvement over 1st-generation tubes was a refinement to S-25 photocathodes. They also enhanced the sensitivity and spectral responses of the devices. The overall increase in sensitivity and gain was enough to obtain bright and clear images with only one intensifier tube.

This greatly reduced the size and weight of NVDs, allowing for headgear-mounted and weapon-mounted configurations. Because they only feature one intensifier tube, they exhibit superior edge-to-edge image clarity and less blooming.

Current 2nd-generation devices produce bright and clear images with a resolution of up to 54 lp/mm. They are available on the consumer market but are, more often than not, subject to ITAR export restrictions.

Generation 3

In the mid-1970s, the introduction of gallium arsenide (GaAs/AlGaAs) photocathodes was a major advancement in intensifier tube technology that marked the emergence of 3rd-generation devices. The new tubes had much greater sensitivity, resolution, and signal-to-noise ratios (SNR), which improved detection range and performance in lowlight conditions. However, due to the chemical interaction of gallium arsenide with the MCPs, these tubes degraded easily.

To solve this problem, the MCP was insulated by a thin film of metal oxide, an ion barrier, at the price of slightly higher electronic noise and lower SNR. Because of the noise, image detail also suffered. Despite these drawbacks, the overall performance was much better than that of 2nd-generation devices.

In today’s market, one can expect 3rd-generation devices with up to 75 lp/mm resolution and superior sensitivity, image quality, and resolution. These devices are under ITAR restrictions and are available only to the military and law enforcement.

Generation 4

4 generations of night vision

In a constant quest for better performance, manufacturers tried to overcome the limitations of 3rd-generation devices with an ion barrier film to reduce electronic noise by attempting to develop filmless intensifier tube technology.

They succeeded to some degree, and this technology was briefly called the 4th-generation night vision, but the manufacturing costs were excessive compared to performance improvements. This terminology was quickly retracted and called 3rd-generation filmless image intensifiers. Currently recognized classification of intensifier tube devices follows generations 0, 1, 2, and 3.

Limitations of Night Vision

Night vision is generally good for seeing large objects and close-ups

The light, range, and size of an object can affect the quality of the image. Night vision is generally good for seeing large objects and close-ups. If you’re looking at an object from a distance, you might not see it in full detail. In other words, it might be out of recognition range, a concept called range detection.

NVDs need light, meaning they cannot operate like a thermal imaging scope in absolute darkness. However, most NVDs include a built-in infrared illuminator (IR illuminator), which acts as a night vision flashlight and makes it possible to use night vision in almost complete darkness.

Additionally, a night vision device cannot operate during the day because there’s too much light. The device amplifies light, so viewing an object during the day could damage internal components sensitive to light.

An NVD’s range depends on the device’s quality and viewing conditions. Most available generation 1 devices can be effective between approximately 5 and 200 yards. The takeaway is that most night vision devices are designed to see in the dark rather than during the day or from a great distance.

Brighter Nights

The brighter scene NVGs provide—which allows pilots to see objects not otherwise visible—increases situational awareness, enhances safety, and improves flight capability. Learn more about our night vision solutions. Please reach out to us today!