Red or Green/white light for reading star charts?

[ColHut]

Dear All,
Perhaps like most of you I currently use a red, dimable, LED torch for viewing my star charts etc. Having read these two discussions, I am absolutely unsure which in fact would be better? I am not an expert and there seems to be genuine disagreement.

See particularly:

http://www.astromax.org/activities/members/kniffen.htm

and

http://stlplaces.com/night_vision_red_myth/

regards.

[Mariner]

Hi Colin,
I briefly skipped over the gist of the articles. They both sound a bit right. I do not know the science of how the eye works so I can't comment as too their factual details. I can say anecdotally as a seafarer who has had to do many watches (8-12, 12-4 & 4-8) over the years that red is my preferred colour - most ships use it for their night lighting within the bridge, in my experience it does not effect your night vision as badly as green - and certainly both are better than white light. I say this with the clarification that light intensity is probably the most important factor in maintaining night vision - more so than colour.

An example: when moving in from the navigation console on the bridge to plot positions at the chart table you must move from a position where it is pitch black (especially when you are in the middle of an ocean) to a position where there is enough light to see a chart. The brighter the light, or more correctly the greater the intensity, the greater the detrimental effect on night vision no matter what the colour.

I find that red led is the best for me, there seems to be a certain glare to green/blue that I find effects my night vision.

[garymck]

I prefer green, I find that to use red effectively I have to have it at a much higher intensity than green There is also the problem that I have great difficulty focusing red at night I often see double or a blur if looking at setting circles for example. Ever tried using setting circles when your not sure of which is the real mark? :) - aging eyes I guess. I find green much easier to focus, an I can have the light at a MUCH lower level....

just my experience, not sure of the science......

cheers

[mikerr]

Gary, what do you use as the green light source?

Michael

[ColHut]

I got the impression that red provided better non-detailed vision insufficient for detailed work at lower intensity, but that maybe green was better for detailed work. But they seem to disagree. Maybe consistent with watch keeping too.

regards

[Paduan]

i learnt a lesson without thinking. i wrote my evenings plan in red ink:screwy:, however it lead me to understand what i was missing in my star atlas.(all the galaxies are printed in red and really difficult to see as they absorb all the red light and disappear.) so as for observing i prefer a green light. i removed a red led from my torch and placed a green led in its place now i can switch between them

[mswhin63]

I think there is no doubt that green lights will work better but in the chart is says and show that the cone and rods are the most sensitive to green light. Yes it will allow you to see you charts well but it will also obviously saturate the night vision. So if you don't mind then go for it.
Photographers use Rubylith light as it is the least sensitive to exposing the film, which is the same system that is used for exposing the eye.
Red lights emit across the major amount of the white light spectrum as well an will also exposure your eyes to excess light. Rubylith lighting is a narrow band of red light and if any one tried to use it provides a good contrast on computer screen and given enough light power produces good visible light as well.

The spectrum doesn't provide levels but you would need to reduce the amount of green light quite substantially to reduce the effect of saturation.

[avandonk]

Just google photopic and scotopic vision. Photopic vision is your bright or day vision from the cones in your eye's retina. Scotopic vision is your night or dark vision from the rods.

Your night vision cannot see red! See diagram below. A very weak green light will not destroy your dark adapted eyes and hence your night vision.

I would try a red and green LED together as a torch and limit the brightness of the green LED so what it illuminates is not easily visible to your day vision in a dark room. That is you cannot see it clearly until you are dark adapted. The red LED can be very bright without affecting your dark adapted night vision. Then you are using both systems without saturating your night vision and thus losing it. This will give you more acuity as night vision is rather poor in the centre part of your retina as cones are far more numerous than rods.


When I worked at Kodak in the late sixties and early seventies we had very dim green lights even when handling Tri-X film! This Tri-X film was five foot wide and 1200 feet long. As film is sensitive to red unlike your eyes nightvision this was far better to minimise fogging of the film as your eyes are about twenty times more sensitive to green than red!

Red safelights are for paper as paper is not sensitive to red light.

The only drawback was it took two hours to get properly dark adapted so we had tea or lunch rooms illuminated by very dim green and red safelights. The red safelights were far brighter than the green.

So finally yes a green AND red LED torch is ideal for looking at starmaps or setting circles. It is just a matter of getting the intensity of the green LED down to a level where it does not ruin your dark adapted night vision.

Hope this helps. Bert

[ColHut]

Thanks Avandonk. Having read and re-read it seems that it's red for the rocks and moving around and dim green for the charts.

regards

[ZeroID]

Interesting. I know that green is the most restfull colour because it is where the eye is most relaxed at focus with. I stare at computer screens all day and at lunchtime will walk out into the garden around the building and 'saturate' my eyes with green trees, grass etc. Helps quite a bit.

I am about to start my Ob build and part of the plan was to use a second PC screen hung on the wall with a red desktop colour the idea being to hang my charts in front of it as a backlight. ( It could also then be used as an extended desktop to run Stellarium or other applications as well ). I might have to look into using a green desktop instead. I can dim it with additional layers of diffuser and by choosing an appropriate green.

Thanks, worth noting for future plans.

[Andrew C]

It seems to me that the overwhelming practical message in this is that colour of the light doesn't really matter, a dim red light or a dimmer green or white light that creates the equivalent response in our eye to the brighter red one will achieve pretty much the same result. I suspect that to some extent, the debate is being somewhat prompted by the fact that most off the shelf green or white lights are designed to be bright rather than dim, and off the shelf red lights just happen to appear duller. So intensity is the key, as many have said.

The proviso, as someone has also said, is that the actual colour of an object on the chart can also affect the result dramatically by selectively affecting its reflectivity to a coloured light source (red objects are hard to see under red light etc).

Another issue that might have a significant impact (which does not appear to be addressed) is if the eye is responding differentially to different colours in ways that we do not directly perceive e.g. even though the dark adapted eye is less sensitive to red light (on which both articles are agreed), the objective intensity of a brighter red light is actually causing our dark adaption rate to be slowed down relative to the duller green one, or some such effect.