NIGHT VISION LIGHTING LAND PLATFORM OPERATIONAL CONSIDERATIONS
By Brian J. Thomson, Oxley Developments Ltd.
This presentation is intended to provoke consideration of some aspects of LAND platform lighting.
The lighting requirements, as for every other technical requirement, derive from the Operational Requirements of the Mission or the Theatre of Operations.
There will be certain physical inputs to the detailed requirement, such as type of terrain, ambient light levels and day or night operation; or both. The enemy capability is a critical input, in terms of night vision, thermal, amplifying optics and weapon sights.
The command requirements for use of NVGs, visual stealth, IR stealth, driving speed or convoy will all affect the lighting requirements.
“What is the place of RED light on LAND platforms?” is a question to consider. The widespread use of red light is traditional; it has always been red! The sensitivity graph for the photopic eye in daylight is well known. This sensitivity is due to colour receptors called cones, which are located on the retina of the eye. At low light levels, other receptors called rods begin to work as we become dark adapted. The rods are much more sensitive than the cones. There is also a spectral shift. Cones and Rods both have sensitivity to red light; the false assumption is that rods are not sensitive to Red.
Our scotopic vision only works at very low light levels, when we are fully dark adapted.
We can perceive green light at lower illumination levels.
To maximise your visual perception, use very low level green light. It is the low intensity that is important for dark adaption. The rods don’t see colour; so if you can see a red light is RED, then you are not dark adapted. On the other hand, if you are fully dark adapted, then you can’t read a map! –There is no colour and resolution is very poor. To operate at night, you need to be somewhere between scotopic and photopic – known as mesopic. Of course, if you are using NVGs, then you will naturally have mesopic sight, due to the intensity of the phosphor image.
“How can we reduce the probability of light detection by enemy image intensifiers?” is a second question for consideration.
There is no standard or specification for IR stealth in the UK. In the mid 1880s, the US Army CECOM at Fort Monmouth released a paper that they called a statement of work. This document describes the requirement to reduce the IR signature of all combat items at Corps level. At the time the aim was reducing the detectability by threat Gen 2 NVGs. The same principles apply to threat Gen 2 NVGs today.
Three objectives were set for “NVG Secure Lighting”. Priority 1 was wavelength restriction. In other words, minimise the Near IR content of the light. The second priority was to reduce the luminance to 0.05 ftL maximum. i.e. minimise brightness. The third priority was to restrict the viewing angle to less than ±10°. So, point the illumination at the operator and nowhere else. These are principles that remain valid today.
IR Secure Lighting is described in the CECOM document as a subset of the NVG Secure Lighting objectives, requiring only the priority 1 objective of wavelength restriction between 700nm and 930nm, maintaining the luminance at 0.5% in this region. This is generally in line with NVG compatibility objectives defined in Mil-L-85762A, so specifying NVG Compatibility will result in IR Secure lighting.
This is an argument for NVG Compatible green light on LAND platforms, avoiding red as being too close to the boundary with Near IR light and detectable in particular with Gen 3 NVGs. These principles can be applied to vehicle dash panels, rear cabins, containers, shelters and tents. It is particularly relevant during troop egress from a vehicle, when light may be emitted.
Covert IR Lights
IR driving lights, that can effectively only be seen using NVGs, m