Seeing Red

How to Maintain that precious seaman’s commodity: night vision

By Chuck Husick

Accident statistics show that safe navigation, especially in conditions that restrict visibility, is challenging. What we see is our primary information resource. In fact, the electronic “aids to navigation” on the bridge, radar and instrument displays can actually hinder our effort to see what surrounds us. Fortunately, there are techniques that can significantly enhance the performance of the eye, and ways to set the electronic displays so that they don’t keep us from seeing what we must see for safe navigation. With a modest investment in additional gear it is also possible to use visual information whose intensity is below what can be sensed by the eye or that may be in forms that are invisible to the eye.

One cost effective and easy way to see better in low light conditions is to ensure that your eyes have been protected from exposure to even modestly bright light for a period before standing night watch. A fatal accident near the Isle of Wight in the English Channel was caused in part by the fact that the watchstander’s night vision was impaired by exposure to bright light just before he went on duty.
Clearly, it is worth doing what is necessary to protect and preserve the eye’s night vision. When trying to see an object in really low light level conditions it’s best to constantly move your eyes across the scene, rather than concentrating on what you believe may be the center of your field of vision. Achieving full dark-adaptation can take as much as two hours during which the eye is protected from exposure to normal intensity of light, however a significant degree of improvement can be achieved by protecting your eyes from bright white light for as little as half an hour. Setting cockpit displays and any lighting to a pure red pallet reduces the chance of loss of low light sensitivity. The difference in light sensitivity between a fully dark adapted eye and one that has been exposed to normal room level lights can be more than 10,000:1.
Other techniques employ electronic technology that will allow us to “see,” albeit through a viewing device. We can use optics, for example a regular 7×50 marine binocular, to increase the amount of light that reaches the eye’s retina. We can use electronic light amplification devices to provide even greater sensitivity. We can use an electronic light amplifier to see in close to total darkness. All light amplifiers operate on the same basis and light amplifier equipped monoculars and binoculars are widely available. Some models include image stabilization.
Although light amplifiers do a remarkable job in delivering useful images they cannot work when there is no light energy at the scene. Fortunately it is still possible to see in this circumstance by sensing and producing a visible image of a different form of energy; the virtually always present infrared energy (normally sensed as heat). Today’s IR sensing devices can create a very useful image even from these small temperature differences. It’s important to recognize that there are limits to what the vision enhancing hardware will show you, and to use extra caution when navigating in low light conditions.
Beyond light amplifiers, which can become overpowering if there is too much light, and the infrared sensitive viewing devices, it is best to think about preserving one’s night vision. A red flashlight or chart light can be used to illuminate paper charts and other objects without concern for compromising night vision. (However, anything printed in red ink will be virtually invisible.) An incandescent bulb coated with red paint doesn’t get the job done.
One of the most immediate detriments to night vision can be the instrument screens in the wheelhouse. Gone are the old CRT bright green radar screens that required a hood to keep the screen from lighting up the bridge. With the advent of LCD screens, and now superior LED screens, the bridge is a far friendlier place to humans’ night vision. Still, if untended they will reek havoc with your night vision.
Nauticomp and Simrad make glass bridge screens that display any signal that is needed on the bridge. At night Nauticomp screens can be easily dimmed to any level from 0 to 100% and, any information coming in on any inputs, including DVI, VGA, and NTSC, can be selectable as “red.” Even with all of the adjustability if you find the red too distracting the screen is dimmable down to 2 nits in black or red. Even the function buttons (non-touch screen) go to red when it is selected.