LIGHT UP DARKNESS WITH INFRARED ILLUMINATORS
A lot of today’s night vision devices usually come with built-in infrared (IR) illuminators. As these illuminators can drastically increase the performance of night vision systems, they are really worth investigating further.
MAKING LIGHT WORK
Before we get to grips with IR illuminators themselves, let’s first take a deep dive into what light actually is and how it is related to the functionality of night vision devices. The light spectrum is made up of different wavelengths, measured in nanometers (nm). For the human eye the visible portion of this spectrum is in the 400nm to 700nm range. Our eyes are not capable of seeing radiation with wavelengths outside this visible spectrum. The colors we see from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Infrared radiation has a longer wavelength than visible red light and is invisible to our eyes. Night vision devices meanwhile are specifically designed to register a wider spectrum than the human eye can see. Which is exactly why they perform better with the assistance of IR illuminators. In case there is very low ambient illumination, or even none at all, an IR illuminator functions as a spotlight for these devices. All this while their beams remain invisible to the unaided human eye.
GENERATING IR RADIATION
There are various ways of creating an infrared light source. One way is to take a high power lamp with a light output visible to the human eye and cover the beam with an infrared filter. This allows the infrared radiation to pass while the visible component of the beam is blocked. This technique is not only cumbersome but more importantly the range of the generated IR beam is rather limited. Enter dedicated IR illuminators. When taking into consideration the IR illuminators for night vision devices on the market today, two general types emerge, LED and laser. In LED illuminators, a semiconductor diode is used to generate radiation at a certain wavelength of the infrared range. Most often you will find LED illuminators with wavelengths of 805nm, 850nm and 940nm. Laser illuminators meanwhile are constructed with laser diodes. The latter type has many advantages compared to the former. One of which is that, having equal power, a laser IR illuminator has a longer range than a LED IR illuminator. This is because the radiation of a laser is more concentrated and coherent than that of a LED. What’s more, lasers consume significantly less power than LED’s to generate the same performance. A disadvantage of laser illuminators compared to LED illuminators is that they can pose possible risks for the human eye when their radiation exceeds Class 1 of laser safety regulations according to the IEC standard 60825-2007. Many countries have specific regulations regarding lasers for civilian use so do not forget to check your local rules before getting involved with infrared laser illuminators.
VISIBLE OR NOT?
There is quite a debate going on in the night vision world about the visibility of infrared radiation. Earlier we concluded infrared radiation is not visible for the unaided human eye. Some claim however that certain game species can still see radiation at wavelengths not visible anymore for us human beings. What’s more, with certain wavelengths, 805nm for example, the radiation emitting source, be it a LED or a laser, still glows up faintly when you look directly into it. Therefore many swear by IR illuminators with a wavelength above 900nm so as to be completely invisible. Others however have experienced trouble free use of shorter IR wavelengths for years. When considering the wavelength of infrared illumination, take into consideration that digital night vision devices can make optimal use of wavelengths both above (completely invisible) and below (faintly visible) 900nm. This rings true for digital devices but is not so for all tube-based devices. Most tube-based night vision devices can only make use of IR-illuminators with a wavelength below 900nm. There are exceptions however so check the small print. What’s more, whereas wavelengths above 900nm will have the advantage of being completely invisible for game animals, their range is shorter than illuminators with a comparable radiation power and a wavelength below 900nm. Whatever the wavelength, take into consideration that other night vision devices can easily pick up your IR-beam, so you are never completely invisible. Which is why professional operators use devices that do not make use of illuminators at all, not to risk giving away their position.
This is one of the defining factors to know how far a specific IR illuminator will take you. Although the detection range of any given IR illuminator also depends on the IR source, LED or laser, the optics scheme, lens quality and anti-reflection coating, radiation power, measured in milliwatts (mW) is a key factor in illuminator performance. In general, built-in illuminators are less powerful than external devices. What’s more, laser illuminators have considerably less power in mW than LED devices for the same performance. As a rule of thumb, the higher the mW value of a given device, the greater its range. Some illuminators have a fixed radiation output while others have a more versatile, adjustable power output.
CREATING THE IDEAL SETUP
When choosing an IR illuminator to create the ideal night vision system, you will get maximal effectiveness when selecting an illuminator with a wavelength at which the night vision device has the highest sensitivity. An illuminator with a wavelength of 940nm for example simply will not work well with a digital device of which the sensor sensitivity is higher at a wavelength around 800nm.
Last but not least, make sure the angle of the illuminator beam corresponds with the field of view of the night vision device. It simply makes no sense having an illuminator beam with a 20° angle when your night vision device only has a 10° field of view. Special mounts providing vertical and horizontal adjustment also help to perfectly align an IR illuminator to create the ideal setup.