Dag Pike considers the age-old adage that using red light preserves your night vision
My guess is that if you step onboard any sailboat at night you’ll find the facility to have a red light at the navigation table.
‘Red light at night’ has been the mantra for every wheelhouse, bridge, helm station and cockpit as far back as I can remember – and I went to sea in 1950.
It is suggested this use of a red light at the helm station followed research undertaken during the Second World War when it became vital to have the best possible vision at night.
It was submariners that set the pace as they needed to be able to adapt to the outside world as soon as possible when they put the periscope up.
That research has set the pattern and now we all use a red light without question, but is it the best solution?
Red light downsides
Helms have changed dramatically since those days with lots of electronic displays and indicator lights, both in the cockpit and at the chart table.
Some of us are old enough to remember that paper charts were once all monochrome, almost all just black and white.
So red lighting worked well, allowing a sharp definition of the monochromatic image.
Additionally, there was not much other lighting at the helm, except perhaps the compass light and, as the compass card was in black and white too, everything worked with a red light which was dim enough to allow a view of the outside world when you switched your vision.
Now we find ourselves in a very different scenario at the helm or the navigation station below.
Electronic displays are lit internally, primarily with a white light source.
So even with a red light at the helm they can intrude on your night vision.
Of course they should all have a dimming switch to put them into night mode but even then can still be a distraction from what you might see in the outside world.
Rods and cones
On a sailing boat you are likely to have just the one display in an otherwise darkened cockpit.
But you may also have sailing instruments that need a light of some sort, so lights in the cockpit could be a distraction.
Problems can arise when someone below opens the companionway doors at night when there is a bright white light on.
That can destroy your night vision for quite a time and even if the light below is red, it may not be the best solution.
Certainly a red light at the chart table will reduce the impact on night vision when the cockpit doors are opened and should improve things when you go below to study the chart or use the radio.
But the electronic screens can still affect your vision and you will take time to adapt.
An expert from the US Coast Guard told me that the use of red lighting to improve night vision is not valid.
Instead it is all a matter of rods and cones.
Without turning this into an anatomy lesson, your eye has rods and cones, which are photo-receptors found in the retina that convert light into electrical signals.
These electrical signals travel to the brain through the optic nerve and are used by your visual system to form a representation of the world.
In other words, this is your sight.
The cone photo-receptors are active in higher light-levels but are non-functional in low-light, and it is these that create our colour vision.
The rod photo-receptors are responsible for your vision in low-light and are more sensitive to light but much less so to colour.
The complicated bit
Now we come to the complicated bit.
The rhodopsin, a chemical found within the rods (night vision) in your eyes is less sensitive to the colour red, which is what led to the use of red lighting at helm stations.
However, now the thinking is to use green or a greeny blue light which allows for better differentiation between colours at low-light levels.
And is, of course, better for picking up definition in today’s multi-coloured charts.
Crucially, this light must be kept at low intensity because both red and green light at higher strength will kill your night vision.
So it seems it is not so much the colour that counts, but the strength of the light you have in the cockpit or at the chart table.
This can be a challenge because, whilst you may be able to dim the electronic displays, you also need to consider indicator lights.
Every switch and control has its own light and to me, it is these lights that affect your night vision.
Many of the controls that have lights do not have to be at the helm and could be located elsewhere.
Otherwise the best solution is to arm yourself with a load of sticky tape that you can put over those irritating lights when on a night passage.
There is another possible solution for us yachties.
You have two eyes, so why not keep one for night vision in low light and the other for looking at charts and displays?
In this way you should be able to get the best of both worlds and it can be achieved by wearing an eye patch!
You simply keep your ‘distance’ eye covered when looking at charts and displays.
This can be achieved by having a patch over your ‘distance’ eye when not looking at the horizon.
Apparently this is why so many pirates are portrayed with eye patches!
However, when looking out of just one eye, your distance perception can be poor and this could put you in more danger when moving about in the cockpit.
After having an eye operation and having to keep one eye covered for a while I found myself bumping into things all the time because I could not judge distance.
It’s probably best to just stick to low-level lighting, but is that possible on modern yachts?
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A delicate balance
Perhaps your navigation lights might intrude enough to make you miss dim lights in the distance.
Deck lighting would be a big no-no but then you might compromise safety.
It can be a delicate balance to have the right level of lighting to be able to move around the deck safely when changing or adjusting sails at night against retaining your night vision.
Ships and boats with wheelhouses seem to have given up on maintaining night vision judging by the displays of lights in wheelhouses.
Under sail you have a better chance and it is best to use the dimmest lights that do the job.
Night vision is a precious safety resource and you need to guard it carefully in the interests of safe navigation.
Installing very dim lighting appears to be the best solution but next time I am going to sea at night I might just dress up as a pirate!
1 Not all about colour
Although red is the accepted colour for keeping night vision intact when going below, other colours such as green and green/blue allow you to better differentiate between colours on a chart.
Red works for monochrome charts but is less effective with the shades of blue and green you find on today’s charts.
2 Intensity matters
It seems an obvious point but the intensity of the light, whatever the colour, is the key concern in terms of maintaining your night vision.
Although most back-lit electronics will have a dimming function for night use it can be surprising how many unnecessary lights there can be onboard.
Cover up any that are not absolutely vital.
4 Time to change
Your eyes can take anywhere from 20-40 minutes to adapt to the change from bright to dim light.
So it is well worth protecting your night vision as much as possible unless you want to be impaired for a decent stretch of time.
Tools to help
At a basic level a torch is useful for pinpointing distant objects when sailing at night.
A lot of marine-specific torches have a dimmer colour setting too for helping you find your way around on deck.
Image intensifiers work by taking an incoming low-light image and magnifying the brightness via an image-intensifier tube.
They do require a certain amount of light, either starlight or moonlight, and will not work in fog, or the complete darkness of overcast conditions.
There are plenty of options on the market for around the £100-300.
All objects emit thermal or infrared radiation, which a thermal imaging unit is able to pick up.
The human eye can pick up thermal radiation at very high temperatures (red-hot or white-hot).
But a thermal imager’s sensor screen detects it at lower temperatures and can identify differences as low as 0.1°C.
A thermal imager converts this information onto an eye-piece screen allowing the user to effectively see in the dark.
Prices start at around £2,000 to some pretty wallet-bashing figures, though a number of cheaper phone add-ons work surprisingly well.