Night Vision - Red Light Myth

[whooshbang]

Whilst poking around looking for a suitable red plastic film to cover my laptop and camera displays and anything else that emits white light, i stumbled across this article.

Apparently all this red light stuff is a myth

Night Vision - The Red Myth

In any case, i'm still looking for some proper red film for my kit so if anyone has some suggestions/shops/online sources i'd love to hear about them, cheers

[iamjulian]

Interesting, but is it fact or fiction? I haven't a clue. I went to a National Trust stargazing event last year where there were a couple of experienced astronomers (most of us were complete amateurs) who were both wearing stupidly bright red head torches. Fine for them, but they were blinding everyone else. They said it didn't matter because the light was red. After being dazzled I wasn't convinced.

[ollypenrice]

Good link and probably true. I remember BrianB discussing this.

However, a red filter is an easy way to dim lights such as the garden solar things I have to help people survive a night's astronomy! It seems to work for me. Another good trick is to have sunglasses handy for when you want to nip into the house where the rest of humanity is behaving normally.

Clearly a bright red light is still a bright light. No one is going to suggest that being squirted in the eye with a red laser is going to help you find Stephan's Quintet in the ZS66...

Olly

[Capricorn]

I would tend to agree that Red is no great use, again from the experience of having a red light shone at me because it was OK. Found that I had to wait to be able to see again with any sort of clarity.

When using a white light I get no worse a wait then using a red.

Makes some sense that green is better, the eye has evolved to be most sensitive to that so a lower intensity should be usable.

[banner001]

well the article is horrendously wrong in many aspects of basic human biology...

basically what happens with human dark adaptation has nothing to do with the rods and cones, its to do with the breakdown of rhodopsin in the eye.

for a given quantity of rhodopsin, and several light intensities, rhodopsin breaks down slowest where long-wavenelgth light (i.e. red) is used.

rod cells give us information about light intensity, whilst the cones provide colour information. the fovea (the area with cones in the middle of your eye that senses colour) is unable to work in dim conditions simply due to there being fewer rod cells there.

so the red light is not a myth, but as stated above that is only for a given lux intensity of light, if it is too bright it will still limit the dark adaptation of your eyes.

in conclusion, you should use the darkest colour of red and the lowest light intensity in order to preserve your dark vision best

[banner001]

and his thoughts on photographic paper are also slightly off, i work in a £200-million pound molecular biology lab, i use the dark room frequently and we have very dark red, low intensity bench lights in there for you to work with, its due to them having the lowest energy transmittance of visible light.

yes you do have a slightly heightened 'Red' channel...but its only a few percent, its a lot better than if you had a higher intensity light in there like a green or a blue...

[anthony]

I have always viewed low level red as the "least destructive" to night vision. Not a requirement at home but just enough to stop you wrecking the place at a star party. I do remember groaning when a bright red head torch was being shone directly into my imaging scope at a star party!

[Moonshane]

well the article is horrendously wrong in many aspects of basic human biology...

basically what happens with human dark adaptation has nothing to do with the rods and cones, its to do with the breakdown of rhodopsin in the eye.

for a given quantity of rhodopsin, and several light intensities, rhodopsin breaks down slowest where long-wavenelgth light (i.e. red) is used.

rod cells give us information about light intensity, whilst the cones provide colour information. the fovea (the area with cones in the middle of your eye that senses colour) is unable to work in dim conditions simply due to there being fewer rod cells there.

so the red light is not a myth, but as stated above that is only for a given lux intensity of light, if it is too bright it will still limit the dark adaptation of your eyes.

in conclusion, you should use the darkest colour of red and the lowest light intensity in order to preserve your dark vision best

I don't know the science as well as you but this matches my experience. I also think, anecdotally at least, that a brighter red light will affect your eyes for a shorter time than say a white or other coloured light will.

[TheThing]

The RN have been using red light to preserve night vision for years, especialally on submarines.

If it's good enough for them...

[jabberwocky]

trucks have a red 'night driving light' in the cab for use when driving at night. it doesnt affect my night vision but then its only just bright enough for me to see where my flask is when i need to pour myself a coffee;)

red is better than white but unfortunately people think that means they dont have to be careful where they shine it.

[ollypenrice]

well the article is horrendously wrong in many aspects of basic human biology...

basically what happens with human dark adaptation has nothing to do with the rods and cones, its to do with the breakdown of rhodopsin in the eye.

for a given quantity of rhodopsin, and several light intensities, rhodopsin breaks down slowest where long-wavenelgth light (i.e. red) is used.

rod cells give us information about light intensity, whilst the cones provide colour information. the fovea (the area with cones in the middle of your eye that senses colour) is unable to work in dim conditions simply due to there being fewer rod cells there.

so the red light is not a myth, but as stated above that is only for a given lux intensity of light, if it is too bright it will still limit the dark adaptation of your eyes.

in conclusion, you should use the darkest colour of red and the lowest light intensity in order to preserve your dark vision best

Excellent post.

Olly

[Earl]

The RN have been using red light to preserve night vision for years, especialally on submarines.

If it's good enough for them...

I have never got that for an underwater by the charts vessel, why need night vision, unless your at the periscope....

Saying that they are a very special breed those Submariners.

[TheThing]

In case they have to surface.

TheThing.

Sent from my iPhone using Tapatalk

[whooshbang]

well the article is horrendously wrong in many aspects of basic human biology...

basically what happens with human dark adaptation has nothing to do with the rods and cones, its to do with the breakdown of rhodopsin in the eye.

for a given quantity of rhodopsin, and several light intensities, rhodopsin breaks down slowest where long-wavenelgth light (i.e. red) is used.

rod cells give us information about light intensity, whilst the cones provide colour information. the fovea (the area with cones in the middle of your eye that senses colour) is unable to work in dim conditions simply due to there being fewer rod cells there.

so the red light is not a myth, but as stated above that is only for a given lux intensity of light, if it is too bright it will still limit the dark adaptation of your eyes.

in conclusion, you should use the darkest colour of red and the lowest light intensity in order to preserve your dark vision best

Excellent post.

Olly

Agreed, that sums it up nicely!

[DaveS]

As an aside, traditionally back-stage lighting in theatres is Blue (Stage Blues). I'm not sure why, I'm still trying to work it out from first principles of visual physiology.

Dave

[skybadger]

I thought this had been laid to rest years ago;Clarkes Visual astronomy of the Night sky had a long tract on this which I can;t be bothered to get out of bed to go and refer to but I am sure it went along the lines of..

Use any light you like so long as the intensity of the source is low compared to the scotopic sensitivity of the eye. Hence you can use any colour if you want, just bear in mind that the brightness should be low to maintain eye sensitivity.

I've not heard of Rhodopsin being destroyed more by one colour light than another. I have seen that rhodopsin is most sensitive to light at 496nm though. (Spectral Sensitivity of the Eye).

So my takeaways would be - no bright lights of any colour. other than that - take your pick. Mine is red, for no real reason. I have two maglights withe their red filters installed and that is quite dim

cheers

Mike

[skybadger]

I just thought I would add this - (Rhodopsin and the eye)

Find the bit that shows where Rhodopsin comes from, and then wonder how many carrots you need to eat to see in the dark like Superman

Mike

[DaveS]

Ah, worked it out.

The audience will be seeing a (Usually*) brightly lit stage, so will be using photopic vision, relatively insensitive to blue, but the crew, working in dimly lit conditions will be using scotopic vision, where peak sensitivity moves to the blue, therefore will be able to see well in a lighting state that the audience won't be able to see.

* though I've plotted my fair share of dim and mysterious (And often blue!) lighting states in my time.

Sorry this has gone a bit OT, apologies for inadvertent threadjacking

Dave

[whooshbang]

Mine is red, for no real reason. I have two maglights withe their red filters installed and that is quite dim

cheers

Mike

Red seems to be the accepted choice so on the strength of that i have found and ordered this from Astro Developments.

Job done and thanks for everyone's comments and opinions on the red myth!

[umadog]

Actually, in bright conditions, cones transmit colour information AND brightness (B&W). It's not true that cones are the providers of colour and rods the providers of B&W. We know this must be the case because foveal vision is needed for reading small B&W text and the fovea contains no rods. Furthermore, rod responses readily saturate in bright conditions, whereas cones do not (http://www.yorku.ca/eye/sensit.htm).

Dark adaptation isn't just the accumulation of more photopigment. The first change which happens is that cones increase their integration times, to average light over longer time periods. This is why "dim light stops play" in cricket. As light levels drop, eventually the lower sensitivity of cones causes them to no longer be able to respond. It is at around this point that colour vision appears to vanish. Rods de-saturate. The retina actually starts to re-wire: cone information partially de-couples and rod information increasingly connects up. Rhodopsin levels build up in cones over half an hour or so. Many processes are taking place at the same time.

The article is right that dim red light is needed, not just red light. I'm pretty sure the stuff about eating vitamin A is a myth, however.

[jamespels]

FWIW, we have two cars - one with a fully dimmable entirely red-lit dash and one with various colours, also dimmable. The one with the red dash is a dream to drive at night but the other is a pain - I find it takes a significant amount of time (up to a second or so) to adjust to looking outside after glancing at the dash, even with the intensity as low as I can get it while still being able to read speed, etc. in a glance.

Far from scientific, but good enough for me.

Incidentally, I have a head torch with a stupidly bright pair of red LEDs; it is OK with just one one but I inadvertently shone it at my face while taking it off and lost dark adaptation for quite a while.

Whatever else anybody thinks, PSP2011 will be red light only from dusk 'til dawn.

J.

[Moonshane]

yes, but James is that DIM red lights? :)

[great_bear]

With regard to this:

For Best night vision:

• Be sure you are getting enough vitamin A or its precursor beta-carotene in your diet (needed for the visual purple).
  
• Green leafy stuff is best followed by vegetables that have an orange color. Yes that includes carrots but spinach or dark leaf lettuce are better.
  

- it's apparently untrue as well, as described here <click>

In summary, extra vitamin A does not assist the night vision of ordinary, healthy people.

[umadog]

I think the vitamin A stuff came from the carrot myth spread by the RAF to distract the Germans from radar.

snopes.com: Carrots and Improved Vision

So the article just propagates other myths. Awesome.

[jamespels]

yes, but James is that DIM red lights?

No more that 2kW, except the laster pointers which we allow up to 10w

Anybody taking this seriously, please don't!!!