Night Vision 101: Seeing in the Dark

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Most of us probably have seen, in the movies or on TV, Special Forces people looking like hybrids of human and machine with sophisticated night vision devices covering their faces, enabling them to see in the dark. Previously, these gadgets were reserved for special agencies and the military. Today, with the advancement of technology and lower costs of manufacturing, these devices have appeared on the consumer market. Even if you are not the type to storm buildings under cover of night, they may prove helpful and greatly enhance your hobbies or outdoor activities. For example, you can use night vision devices for:

  • Wildlife observation
  • Night fishing and boating
  • Night hunting and paintball
  • Camping, scouting, and exploring caves
  • Search and rescue
  • Hidden object detection
  • Performing nighttime repairs
  • Discovering who visits your backyard at night
  • Pulling pranks on your friends and family

When it comes to night vision, most of us naturally and correctly assume that these products enable us to see at night. However, there are different types of night vision technologies that have different uses and capabilities. Under the umbrella term “night vision,” experts usually differentiate between three main types: image intensifier night vision, digital night vision devices, and thermal imagers. Despite many differences, they all share common architecture: an optical tube that is customized for imaging infrared light and an integrated infrared sensor that converts invisible infrared light into visible light, which can be seen and analyzed by the human eye. 

Night Vision Image Intensifiers

"The infrared light that is generated by the stars reflects from the Moon and forms the ambient infrared illumination that is used by night vision devices at night."

We are familiar with the image produced by the intensifier tubes that we have seen on movies, news, or popular science publications: it is an optic that produces green and black images. Intensifier tubes use reflected ambient infrared radiation, invisible to the human eye, to generate images of the view. Just like the visible light, this infrared radiation is emitted by the Sun and the stars, and illuminates everything—including the Earth and the Moon. The infrared light that is generated by the stars reflects from the Moon and forms the ambient infrared illumination that is used by night vision devices at night. Intensifier-tube night vision devices convert the infrared light reflected from objects and convert it to visible images. At the heart of these devices are the intensifier tubes, which are constructed of tubes that have a photocathode at one end, an internal anode in the middle, and phosphor screen on the other end. High voltage is applied between the photocathode and the anode to create a strong electrostatic field. When infrared light strikes the photocathode, electrons are emitted and accelerated by the electric field toward the phosphor screen, which produces a visible image. Since the inception of these devices, their basic principle of operation has remained basically the same; however, resolution, clarity, and image brightness have improved significantly over the years.

Terminology

Before we dive into the technical discussion, it is prudent to familiarize ourselves with some common night vision terminology.

Sensitivity: defines the minimum amount of infrared light that can be detected

Gain: the ratio of visible output to the amount of infrared input; a measure of signal amplification

Noise: the output signal on the phosphor screen that is not related to the actual infrared image; noise distorts and blurs images

Photocathode: a negatively charged screen/electrode coated with photosensitive material; absorbs infrared light to produce electrons 

MCP: a micro-channel plate; used in amplification of photoelectrons 

Anode: a positively charge electrode; accelerates electrons toward the phosphor screen

Phosphor screen: this absorbs electrons generated by the photocathode and produces the visible-light image, which corresponds to the original infrared image 

ITAR: the “International Traffic in Arms Regulations” the regulates the export and sale of certain controlled technologies outside of the United States

Active devices: night vision devices that use infrared (IR) illuminators to cast additional or supplemental light on targets for imaging

Passive devices: night vision devices that use natural infrared illumination for imaging

The Generation Gap

Generation 0

Generation 0 is the oldest image intensifier technology, dating to its first military use during World War II, by the German army. The concept of operation was inspired by the RCA Corporation’s image-converter tubes, developed in the mid-1930s for use in televisions. 0 generation photocathodes, called S-1 cathodes (AgOCs), had very low efficiency, low gain, 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 a generation 0 to a generation 3, resulting in improved sensitivity, resolution, image clarity, brightness, and image color, but 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 a 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. Another drawback was that they produced images with a clear and bright center but distorted darker edges. Additionally, 1st-generation tubes exhibited image blooming, a momentary image washout due to an overexposed phosphor screen. Today, Generation 1 night vision devices have the same basic design but, thanks to improvement in manufacturing processes, produce images with resolution of up to 35 lp/mm. This technology is available to consumers and typically is not subject to ITAR export restrictions.

 


Firefield 1st generation IIT night vision handheld monocular with IR illuminator

 

Generation 2

 

2nd-generation in night vision technology was born around the late 1960s with the introduction of micro-channel plates (MCP) inside the intensifier tubes. MCPs amplify the number of electrons reaching the phosphor screen thousands of times, which greatly increases the device's gain. Another significant improvement over 1st-generation tubes was refinement to S-25 photocathodes. They also enhanced sensitivity, as well as 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 resulted in greatly reducing the size and weight of NVDs, which allowed 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 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.

 


Armasight 2nd generation IIT night vision riflescope clip-on

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 low-light 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 resolution of up to 75 lp/mm and superior sensitivity, image quality, and resolution. These devices are under ITAR restrictions and available only to military and law enforcement.

 


Night Optics 3rd generation IIT night vision riflescope

Common Features Available with 2nd- and 3rd-Generation Intensifier Tubes

White Phosphor

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


White Phosphor IIT night vision image

Green phosphor IIT night vision image

Automatic Brightness Control (ABC)

ABC is a feature that controls voltage across the micro-channel plate to regulate its gain according to the amount of external light that enters the tube. It helps to maintain constant image brightness, while the external illumination is varying.

Bright Source Protection (BSP)

If an intensifier tube is exposed to daylight or to a flash of bright light at night while it is on, it may become damaged or burn out. To prevent this, some night vision products incorporate Bright Source Protection (BSP), a feature that turns the photocathode voltage off when it is exposed to bright light. The BSP prevents tube degradation and extends its life.

Autogating

To allow the image normal performance under bright-light conditions and to reduce degradation, the power supply generates rapidly oscillating photocathode voltage. With this feature, the bright light does not overload the tube. Autogating maintains high visibility, image resolution, and extends tube life in excess of 15,000 hours without noticeable degradation.

Generation 4

In a constant quest for better performance, manufacturers tried to overcome limitations of 3rd-generation devices that have ion barrier film, namely 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 generation 0, 1, 2, and 3.

Digital Night Vision

The digital night vision is the least known type of all in the consumer market. As implied by the name, these devices use digital CCD (charge-coupled devices) or SMOS (complimentary metal-oxide semiconductor) sensors, similar to those in your digital camera. Because the CCD and CMOS sensors have sensitivity in the Near Infrared spectrum, up to 1.1 µm, they are used in Digital Night Vision devices. This type of night vision offers several advantages.

 


Konus Optics Digital night vision monocular with IR Illuminator, USB and Video-Out ports
  • Their digital sensor is resistant to damage from bright light
  • They do not burn out easily and have a virtually unlimited lifetime
  • They are less fragile and less expensive.

In addition to all of the above, digital night vision is inherently easier to integrate with digital media recording and storage. Of all the night vision products available on the market, these are the least expensive, easiest to use, and most reliable.

Infrared Illuminators

Because digital and intensifier tube night vision devices are passive devices and use natural ambient infrared light from the Moon and the stars to create an image, they will not work effectively on cloudy nights or in the total darkness of a basement or blacked-out building. To gain visibility, improve sensitivity and range in total darkness, many NVDs come with a built-in infrared illuminator or have a mounting point for an optional illuminator of your choice. Theoretically, any source of infrared light could serve as an infrared (IR) illuminator for your night vision device: infrared lamps, infrared LED flashlights, and infrared lasers. Because LED and laser technologies are more widely affordable on the consumer market, infrared lamps are less common today. The vast majority of commercially available dedicated night vision illuminators use eye-safe lasers or LED sources.

Thermal Imaging

The last and the most sophisticated technology in the category of night vision is thermal vision or thermal imaging.  Thermal imagers are unique in many aspects, but what sets them apart is that they do not detect reflected ambient near—and short-wave infrared light (SWIR), but rather detect heat (long-wave infrared light, or LWIR) emitted by objects. Any object with a temperature above absolute zero degrees Kelvin emits long-wave infrared light (heat). The warmer the object is, the more infrared it radiates and the more detectable it is with thermal imaging. To do this, thermal imagers use very sophisticated detectors—bolometers—that are also sometimes referred to as focal plane arrays (FPA). They read the difference in temperature between an object and its background to create a thermal profile of the scene, which is then shown on an electronic display. Thermal imagers usually use germanium optics, which are opaque to visible or near-infrared light and will not detect it. 

 


Torrey Pines Logic T10-S Thermal Imaging System

To make thermal images visible to us, these devices utilize specialized electronics that process data from the imaging sensor and relays it to a built-in or external display. The display can be one of the following types: LCD (Liquid Crystal Display), OLED (Organic Light Emitting Diode), or AMOLED (Active-Matrix OLED). Contrary to intensifier tubes and digital night vision, they can operate in total darkness without IR illuminators or during daytime and allow you to see the thermal signature emanating from humans, animals, jet or combustion engines, or hot wires. Because the infrared spectral band they use has slightly different properties than visible or near-infrared light, they also allow you to see clearly through fog, smoke, foliage, and dust—but not through windows or windshield glass.

Thermal imagers are also frequently used by law enforcement to investigate crime scenes because they allow differentiating between cars that were recently driven and those that have been parked for a long time. Thermal imaging also enables detection of objects that were recently touched or held by people and still retain body-heat and those that were not touched. One significant disadvantage of thermal vision, compared to night vision, is its lower image resolution, which makes it difficult to recognize faces.  For many years, thermal imagers used very bulky, heavy, and expensive cooled bolometer sensors that were impractical for consumer use. Even with the introduction of non-cooled microbolometers, which are much more compact, lightweight, and consume less power, the technology was very expensive and only accessible to the military, law enforcement, scientific research, and companies that could afford it. In recent years, when manufacturing cost dropped, thermal imagers became available for the consumer market.

Hybrid Thermal/Night Vision

To combine the advantages of both night vision devices and thermal vision, manufacturers are developing hybrid thermal/night vision imaging systems that incorporate both the image intensifier technology and thermal imaging in a single device. With this hybrid technology an operator has the option of viewing thermal-signature, high-resolution night vision imagery, separately or in combination, on the same display. This allows superposition of high-resolution night vision images with thermal profile and the ability to see through heavy smoke, as well as glass. Another trend is underway that aims to go beyond known 3rd-generation night vision by directly integrating a CMOS sensor into the intensifier tube instead of a phosphor screen. This approach offers direct video output for viewing and transmission to command centers for monitoring and gathering data for intelligence. Most of these technologies are still in the early development stages, and some are only available to military and law enforcement.

While some of the newest night devices and thermal imagers are out of reach for most people because of price or restrictions, there are plenty of cool, good-quality digital, 1st-, and 2nd-generation night vision devices, as well as some thermal imaging products that can greatly enhance your hobbies and professional and outdoor activities. When choosing your favorite, keep in mind that most consumer versions are available in a variety of configurations, depending your hobby or use: monocular, binoculars, bi-oculars, head- or helmet-mounted designs, riflescopes, sights, or riflescope clip-ons.

Don'ts of Night Vision and Thermal Imaging

  1. Do not expose intensifier-tube devices to bright light or the day.
  2. Do not leave the device on when not in use.
  3. Do not drop or shake.
  4. Do not touch the optical elements with fingertips.
  5. Do not leave batteries inside during storage or transport.
  6. Avoid exposure to moisture unless the device is waterproof or water resistant.

Dos of Night Vision and Thermal Imaging

  1. Consult manufacturer's instructions before use.
  2. Keep devices clean, especially lenses.
  3. Use recommended or included case for storage and transport.
  4. Use lens caps, when possible, to protect optics and tubes.
  5. Store in cool and dry places.

8 Comments

Hi, would you recommend any digital night vision scope below $1,000?

I would recommend the SiOnyx Aurora Black Full-Color Night Vision Camera. The SiOnyx Aurora Black Full-Color Night Vision Camera is a tactical night vision solution for those who need full-color night vision capability at an affordable cost. It is sensitive to wavelengths from 400 to 1100nm, and it provides a full-color image with light levels as low as 2 millilux. This enables you to record color images under near-moonless starlight.

https://bhpho.to/2VJWoc4

i use a chapstick lid as a lens cap for my torrey pines t12(pictured above) since one is not supplied. works great, but if you wish to do the same, BE SURE to heat up an allen key, screwdriver, etc and flatten down the plastic 'knub'  inside so as to not scratch the glass with what you're trying to protect it with. very cool little unit. enjoy life, none of us has quite as much time as we might suppose.

Thanks for the advice, glusniffer! And, thanks for reading!

Excellent and absorbing dissertation.  Thanks!

Wow! These thermal imagers are cool! I mean, hot! Well medium maybe.