Quality images are a necessity for any security system or transport monitoring application. Not only does the performance of the system rely on the camera and lens, but also on the quantity, quality, and distribution of available light. Light determines whether a subject can be viewed at all, and at what distance. The quality and direction of the light also controls the appearance of the subject. However, there are lots of different types and wavelengths of light available, so which should you be considering for your project?

White-Light

White-light is one of the most widely used wavelengths and one of the main advantages of using white-light as part of a security system is its ability to provide colour images (providing it is used with a colour camera). Being able to positively identify the colour of someone’s clothes, hair, or other features, could provide crucial evidence for prosecution.

The defining characteristic of white-light illumination is that it is highly visible to the human eye, hence its use for general area illumination. For surveillance applications, this is also useful when using white-light as a deterrent to ward off potential intruders. On the contrary, if covert surveillance is the aim, white-light illumination is unlikely to be the answer.

Additionally, using constant white-light at night may not be suitable for all applications, due to the fact that the target area is lit up, and therefore, potentially assisting an intruder in undertaking a crime. When using white-light, consideration also needs to be given towards light pollution. While the use of LED technology means the light can be targeted accurately, some applications may be restricted in their ability to use white-light for environmental reasons such as protecting the night sky or wildlife.

Infrared (850nm)

Infrared 850nm wavelength is a semi-covert light and is generally the preferred choice for most CCTV systems. Security cameras are most receptive to this wavelength of IR and, therefore, it gives the best night-time images. Being semi-covert, the illuminator does give off a slight red glow, visible up close or when looking directly into the light.

However, for most applications this is not an issue and Raytec recommends the use of 850nm over other wavelengths of IR. According to Raytec, 850nm will provide the best night-time images and allow the camera to perform at its optimum.

Infrared (940nm)

940nm is a fully covert wavelength of IR light. A 940nm illuminator does not emit any red glow, making it an option for applications where the red glow from an 850nm light is deemed unacceptable.

However, the Raytec paper states that the use of 940nm will mean a significant drop in image quality and achievable distances when compared to an equivalent level of 850nm light. The performance sensitivity of the camera will drop by as much as 50% compared to 850nm.  As a result, where possible the company stresses that it would always recommend the use of 850nm over 940nm, and that when installers are using 940nm, that they should always ensure a suitable camera setup is being used.

Hybrid

Another option for consideration by specifiers is the use of Hybrid illuminators. Hybrid illuminators provide an all-in-one solution, combining both IR (850nm) and white-light into a single unit. This means one illuminator can be used for both covert surveillance, and as a white-light deterrent. This is commonly used for surveillance systems where the end user would like to ward off an intruder before they commit the crime.

Far-Red (730nm)

Looking beyond white-light and infrared, a wavelength of 730nm (known as ‘Far-Red’), is becoming an increasingly popular choice for transport applications where driver or passenger identification inside the vehicle is required.

Modern windscreens are designed to block out certain wavelengths of light. This is mainly to protect the occupants of the vehicle from ultraviolet (UV) rays but is also an attempt to keep the cabin cool by blocking a proportion of infrared (IR) light. 730nm is commonly used as less light is blocked by the windscreen. Raytec has conducted some tests in order to highlight the purpose of seeing through windscreens. The results showed that the 730nm light provides the clearest images to identify the individual within the vehicle (compared to the other wavelengths discussed above).

However, one downside is that a 730nm illuminator does give off an obvious red glow, which could become distracting for drivers in certain cases. In an ideal world, the quality of images produced using 730nm could be achieved using an illuminator which gives off no visible light (and, therefore, offers no distraction to the driver). However, in reality, the further down the spectrum one moves, the more light becomes visible to the driver.