Purpose of blue light?

[2xTrinity]

Right and wrong:

Retaining Night Vision
To retain your night vision, a red light has been the traditional choice since before WWII when
the military settled on red as the best choice. Recently, there has been a move to green and
blue-green light, precipitated in large part by the military's change to green, which itself has been primarily motivated by the increased use of night vision equipment. Which is really better? As it turns out, green light offers some advantages over red as a means to retain night vision capability. However, it isn't cut and dried.
Total brightness, or illumination level, of the light has a potentially more significant effect on night vision retention than does the choice of red or green. Because your eyes are more receptive to green light, we gain better visual acuity at lower light levels than when using red light. Green also allows for differentiation between colors that red does not and the magenta used on aviation charts, for example, is readily readable under green light, not always the case with red.
Both reasons contribute to the fact that pilots and many others generally seem to prefer green
over red, it simply makes it easier to see and read in the dark cockpit. The potential problem is with the actual illumination levels we use, not the color of the light. The brighter the light, the more negative impact on night vision, both in our capacity to see and in how long it takes to gain back optimum night vision. This is true regardless of whether it is red or green.
Ideally, you want to use only as bright a light, red or green, as is necessary to perform your chores and no more. However, if you have a brighter light than you actually need, a brighter green light will generally have a more negative effect than an equally bright red light. Green or
blue-green has a greater capacity to adversely affect night vision because the eyes are about 100 times more sensitive to these colors, so even moderately too bight light can have a serious deleterious effect.
Another complication is that an individual's visual acuity at low light levels varies quite a bit, so what would be perfect for one, might be too bright or too dim for another. In other words, without some means to vary intensity, odds are no light will be perfect. Bottom line is that red or green will both perform adequately, but what you really should be more concerned about is to avoid very high illumination levels, of either color, if retaining night vision acuity is your goal.


http://www.kriana.com/pages/nightvision.html

They were essentially saything the same thing my post did.

One nitpick:

Saying that green allows "better differentiatin of color" is misleading. With a single color light source, one can't differentiate colors at all. For that matter, if the light is bright enough that what you are shining it on actually looks green, it's too bright.

Green light provides better contrast since it is in the middle of the spectrum -- many things reflect it to differing degrees, few things absorb it completely. So you'll see things in lots of shades of gray. Hoewver, with red light, there are tons of things that absorb it completely (such as leaves), and others that reflect it completely (eg the magenta ink in their example). So useful contrast is less. In this case, green is definitely better, for that matter, an extremely dim white light is an even better choice still, in case someone happened to use a light green ink... that is, provided that the light is kept so dim that there's no "color differentiation" even though the light is white.

However, red light CAN be used at much higher illuminances than green. For example, I can flip on a red \lamp inside an observatory to read a star chart, then get back to looking at stars with no difficulty. And star charts aren't printed in magenta ink, so no problem there. On the other hand using a very very dim white or green light, with enough brightness to read the chart at all is enough have a detrimental effect on night vision.

I agree with this article that there must still be a practical limit to the red brightness -- if the light is bright enough to create after-images, those will still interfere with my vision even though my rhodopsin may still be there.

On the other hand using a very very dim white or green light, with enough brightness to read the chart at all is enough have a detrimental effect on night vision.

2xTrinity: Okay: How do you know?

Hee hee!

My liteflux LF2x on its lowest setting on NiMH produces 0.2 lumens. It is currently hosting a 5A neutral white emitter. I have taken it camping and used it for night-hiking successfully. As long as I'm in the dark for about ~15 minutes first, and am careful not to shine the light on anything too reflective or too close to me, it is enough to see clearly where I am going.

If 0.2 lumens isn't quite enough (eg, if some genius thinks its funny to shine his half-dead 3D maglite directly in my dark-adapted eyes) I go to my "fall-back" light kept discretely in my jacket pocket -- a 2C Mag '61 w/ SMO reflector (1000 lumens in a very concentrated beam which nobody ever sees coming...) Then, after nuking everyones night vision, I can ramp my LF2x up to more like ~50 lumens so we can still see where we are going on the way back...

 

[ruriimasu]

it is interesting that while i was looking at this thread, there is a news article on the calming effects of blue lights 😕

 

[darknessemitter]

As it turns out, green light offers some advantages over red as a means to retain night vision capability.

I understand what you're saying later in the post about possible value in sacrificing some of your rhodopsin to see with sharper detail by using green light, but sacrificing rhodipsin is the opposite of "retaining nightvision capability". The rest of your post is clearer, but that first sentence may confuse people.

EDIT: I guess I should've clicked the link first, I didn't realize that the whole text was excerpt from the article. But regardless of who wrote it, the first sentence is misleading.

 

[Dead_Nuts]

I believe there is a model of the Tomahawk that has res and green emitters around the primary reflector. That would give you both colors. (Mine is red/blue)

 

[defloyd77]

it is interesting that while i was looking at this thread, there is a news article on the calming effects of blue lights 😕

Wow that is very interesting. Oh no, I can now see light makers selling blue led lights as a self defense tool that makes bad guys not wish to harm you.

Kind of makes sense, I think I've read about blue lights helping people with seasonal affective disorder, so I'm sure it works for a pretty similar reason. http://www.news.harvard.edu/gazette/2006/02.09/01-blue.html

 

[N/Apower]

Wow that is very interesting. Oh no, I can now see light makers selling blue led lights as a self defense tool that makes bad guys not wish to harm you.

Kind of makes sense, I think I've read about blue lights helping people with seasonal affective disorder, so I'm sure it works for a pretty similar reason. http://www.news.harvard.edu/gazette/2006/02.09/01-blue.html

No lie? I really dislike holidays. Breaking up last christmas morning did not help. Perhapse I will look into some blue lighting for my bedroom or something.

 

[electrothump]

I've had little use for the blue leds. The blood I saw was nothing more than black spots, and you really had to know where they were in order to see them at all. So, no,,, the blue leds on a ROV Xtreme headlight do not show blood any better than the moon. Absolutely no help. One thing I did notice about the blue though is that it doesn't make the reflectors on the back of the car reflect. The red and white do a fine job, but no reflections from the blue. I thought that to be kinda odd. Plus, the blue and red leds will still light the way after the battery gets to weak to power the white led. All that being said, I really like the little headlight. I now have three of them. Car Quest autoparts stills sells them for about 14 bucks.

DN

 

[defloyd77]

Red doesn't reflect with blue, because there isn't blue in red. Have any of you tried blue and red with blood yet?

 

[bsharke]

In my experience red light preserves night vision fairly well, and the dimmer it is the better.

As far as tracking blood goes, last year I tried this out in the pitch dark on some fresh gore from a deer kill with both a blue LED and blue incan with a filter. Neither light had any significant effect on the blood that I could see.

It appears to me that the blood tracking ability of blue light is a hyped-up feature intended to sell more lights to pessimistic hunters. Their best bet would be to stop shooting earlier in the day and take care of business while the sun is up.

Cliff....you are right on with this thread. A true blood tracking light must have a combination of red and white (red 2-1/2 times white is ideal i.e. 10 red to 4 white) led to really make the blood glow bright red. A UV LED blacklight will actually make the blood appear a lighter shade of brown.

 

[ConfederateScott]

I've said it before and I'll say it again, people who claim that blood "stands out" under blue light have never tried it themselves. More than likely they are repeating something they've heard or read and think it's true. But it's not true. It's a modern day wives tale. In fact (yes, from personal experience), blue light makes blood look black. If blood were on white paper or snow it would make it stand out simply from contrast. But on the leaves, grass, soil, etc. having black blood isn't an advantage over red. It's a disadvantage. A good 'ol incandescent light like a 6P is the best blood tracking light I've tried. The best use I've found for my Inova with blue LED's is to follow a trail of flourescent orange flagging tape to my deer stand early in the morning before daylight. The orange tape lights up under the blue light.

 

[Guy's Dropper]

I have a small keychain light with a blue led that I've had for a number of years. It is probably just this particular light, but it seems to make the most shades red, orange or green colors really stand out. If I didn't know any better, I'd sat they were fluorescing. I have a larger UV light that has a similar effect on dust and the same colors as the blue light.

 

[darknessemitter]

I have a small keychain light with a blue led that I've had for a number of years. It is probably just this particular light, but it seems to make the most shades red, orange or green colors really stand out. If I didn't know any better, I'd sat they were fluorescing. I have a larger UV light that has a similar effect on dust and the same colors as the blue light.

A lot of things do fluoresce under blue light, including a lot of commonly used inks and pigments.

 

[chiphead]

Blue light = special
Red light = Roxanne
Dashboard light = Paradise

etc. :nana:

Yea!

 

[Hitthespot]

I have a couple of blue lights, the poor things got that way from not using them too much. :nana:

Bill

 

[LightScene]

These color threads always wander into the night-vision realm. Astronomers find that low level white light works best for being able to see what you are doing and still retain night vision. 2xTrinity has already pointed this out, and I just wanted to back him up.

You really need a variable intensity light to get to the perfect setting for your own eyes, depending on how much ambient light there is.

 

[applevision]

Not to be a pain in the neck, but I'm really interested in this question in general. My sense is that we can summarize what the purpose of blue light is:

1. May be helpful for maintaining night vision (I'm still not totally clear on this and I wish there were a really definitive way to put this to rest)

2. Good for Seasonal Affective Disorder: although we know that this must be used with the proper brightness, in the peripheral vision, at specific times of day for this to actually matter in this regard; there is very good science to back that up.

3. May have a "calming effect"

What am I missing?

Things that it seems it is NOT good for:

1. NOT good for finding blood (I think the folks who argued against this in this post were very convincing, esp. those with first-hand experience and testing).

What else?

It will be nice to have a summary for future reference so we can refer to it! Let's make a CPF Consensus Statement! :naughty:

 

[defloyd77]

My 2 cent summary: bad for night vision (compared to red at a given level), bad for blood by itself, good for blood along with red light, good for dusting, good for finding things that fluoresce, good for waking you up and possible treatment for SAD and bad attitudes.

 

[darknessemitter]

Not to be a pain in the neck, but I'm really interested in this question in general. My sense is that we can summarize what the purpose of blue light is:

1. May be helpful for maintaining night vision (I'm still not totally clear on this and I wish there were a really definitive way to put this to rest)

Wait, what? Where was that in the thread? Blue does not have any special properties for maintaining scotoscopic nightvision, that's what red is for, because the rod cells aren't bleached out by it, I thought we've already been over this in this thread? :shrug:

 

[petersmith6]

i have a Blue led for night Diving,blue is the last colour to be absorbed by water.As for night night work i prefer blue as its closer to moon light but have been playing with Green LEDs ,Verey low powerd green leds can iluminate a hell of a lot.

 

[iapyx]

I have a question for which I don't want to start a new thread, so I try this existing thread. It's in the same area:

Can anybody tell me why Surefire doesn't make (as far as I know) yellow filters? The idea is that yellow light cuts through fog easily. At gas stations one can buy yellow sunglasses for when it's foggy outside. Incans cut through fog better too. (light frequency)
The question is: if I had a yellow filter for my U2A, would that improve my sight at foggy areas. Or maybe not?

Do blue or red filters give better results than yellow filters?

thanks and sorry if this question has already been discussed (couldn't find it).