A red light headlamp for biology field work in the rain

I read the excellent review by Bolster on things to consider when purchasing a headlamp, so I have been able to narrow down the search a bit. My daughter will be doing field work in Central America for nesting sea turtles. They nest at night and only red lights can be used and the season is typically rainy. She will have to ride a bike in the dark to the site, scan the beaches, but also do focused recording on notebooks, etc. So, need redlight flood, and spot?, waterproof and comfortable (shifts are 3 hours). I think the following may be ok, but not sure: Petzel Tikka, Black Diamond Spot, Zebralight and anyone know about the Silva Ninox? Suggestions would be most appreciated! Thank you.

I'm a little confused: must all of these activities be performed with red light?

The one I'd suggest strongly considering is the Petzl Tikka XP2, unless you actually mean all of these activities are to be performed in red light. The Tikka XP2 is extremely versatile with both flood and spot as well as a red LED for red beam output.

Maybe one of Zebralight's offerings would be a good choice.

The Zebralight H51R and H31R are bright (100 and 110 lumens)
They all have many modes, so it will easily run trough a shift. The H51R uses a common AA battery, the H31R a CR123 battery.

I guess they are quite floody and throwy, typical Zebralight.

I'd recommend the Princeton Tec Apex with the RED 5mm LEDS. This would give her two brightness levels of red light, plus the option of a bright white light for riding her bike (or any other situation where a red light isn't going to work well). Because the two colors of light have their own buttons, there's less of a chance of accidentally turning on the white light when she meant to turn on the red. And the 4xAA battery pack means longer runtimes between battery changes (very important when working at night!).

Also, I'd MUCH rather trust the waterproof Apex out in the rain than a Petzl or Black Diamond.

The Black Diamond Storm is waterproof but the red LED isn't all that bright. The red LED on the Petzl Tikka XP2 is brighter. The main issue with the Petzl might be that the white LED setting for low isn't very low and the high isn't very high compared to some other headlamps.

The new Zebralight red LED only model mentioned sounds like what she needs for the turtle studies. Any headlamp will work if it's bright enough for riding her bike. You could get her a relatively inexpensive PT EOS for that.

The XP2 isn't waterproof by the way. The EOS and Storm are.

So many choices

I've posted extensively on this topic, both here and in the general flashlights forum; I know a lot about this as I hold a PhD in perceptual psychology and am a professor of cognitive and physiological psychology. If you check my profile you'll be able to find my posts on this topic; it will be easier than trying to do a search.

If she's going to be doing things like taking notes, riding a bike, etc., she does NOT want a red light. On the contrary, she'll want what's called an "NV Green" light. Just as a prelude to the extensive discussion on this by others as well as myself, the short version of the story is that red is best only for preserving night vision. If you have to do any kind of activity requiring good depth perception and acuity while dark adapted (such as riding a bike, and taking notes) the NVG lights are superior in every way.

Lastly, I would recommend she NOT try riding a bike with a light that's so dim it will preserve dark adaptation. Rather, get her a good light that will allow her to see well ahead of her bike and advise her to arrive half an hour early and avoid all light sources for that time to become dark adapted. That will both safer (bike riding) and more effective (preserving night vision) than trying to ride a bike with a sub-lumen light.

Does it have to be red?
I remember from another thread, that amber is acceptable to prevent interaction with sea turtles
http://www.axiomled.com/AxiomLED/Sea_Turtles.html

Many thanks to all who have replied, this has certainly helped in sorting out what we need. A waterproof and durable light is important as the area is fairly remote and work will occur during rainy season. I will check with the organization to see if a red light is absolutely required. Good point about not bike riding with a red light. For field work I was thinking the red Zebra light would be a go, but if a red light is not required, I'm back to square one with which light to purchase. Is there is a durable, waterproof, green and red light available?

Do a google search for "Rigel Systems".

B0wz3r said:

I've posted extensively on this topic, both here and in the general flashlights forum; I know a lot about this as I hold a PhD in perceptual psychology and am a professor of cognitive and physiological psychology. If you check my profile you'll be able to find my posts on this topic; it will be easier than trying to do a search.

If she's going to be doing things like taking notes, riding a bike, etc., she does NOT want a red light. On the contrary, she'll want what's called an "NV Green" light. Just as a prelude to the extensive discussion on this by others as well as myself, the short version of the story is that red is best only for preserving night vision. If you have to do any kind of activity requiring good depth perception and acuity while dark adapted (such as riding a bike, and taking notes) the NVG lights are superior in every way.

Lastly, I would recommend she NOT try riding a bike with a light that's so dim it will preserve dark adaptation. Rather, get her a good light that will allow her to see well ahead of her bike and advise her to arrive half an hour early and avoid all light sources for that time to become dark adapted. That will both safer (bike riding) and more effective (preserving night vision) than trying to ride a bike with a sub-lumen light.

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I agree it would be a bad idea to use only red light for the bike ride, but why would red light be a problem for taking notes unless you were using red ink or red-lined paper?

Also, I suspect the main reason for the red light might be to avoid disturbing the turtles too much. Some animals have low sensitivity to red light, though I'm not sure if these sea turtles fall into that category.

darknessemitter said:

I agree it would be a bad idea to use only red light for the bike ride, but why would red light be a problem for taking notes unless you were using red ink or red-lined paper?

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If the light is one of the common red lights that's used for night vision purposes, she will be able to use it adequately for things like note taking. The problem with this is that those kinds of lights have their output in the 620 nm range of wavelengths, which is still in the range of the cone receptors, and if they are active, dark adaptation cannot take place. A true night vision red light should be what's called a 'deep' red, in the range of 670 nm or so. This is far enough up the visible spectrum that the cone receptors, specifically the long wavelength or red receptors, will only be activated a very little at this wavelength, and allow true dark adaptation to take place.

When true dark adaptation occurs, the cones are shut down, they don't send any signals to the brain because there isn't enough light to activate them. However, the rods are still sensitive at these much lower levels of light. This is what's known as scotopic vision, based only on the rod receptors. All high acuity vision, which is what's necessary to be able to read or see small details occurs only in the cone system, and only in the fovea, the center of the retina. It's the spot in the retina that directly corresponds to what is right in front of our eyes, what we're looking directly at. So, when truly dark adapted, high acuity vision is impossible, so she wouldn't be able to take notes, read, etc. because she has no acuity in her visual input.

An NVG light on the other hand, is at a wavelength around 500 nm, which is in the green/cyan range. This is the frequency at which the rods respond best. The green cones also respond here, so keeping an NVG light at a low level is crucial to maintain scotopic vision. When using an NVG light, it can be set at a level where the observer is at the cusp between the photopic/scotopic break point. The cones can be activated very slightly and high acuity vision is possible, while still maintaining true dark adaptation.

In either case, there is a simple rule to know if your light is too bright or the wrong wavelength for true dark adaptation. If you can see the color of the light, it's too bright; you are activating the cones and cannot go into full dark adaptation. This is true for either red or green lights because the rod system, which provides scotopic vision, is color blind, it does not send any signals to the part of the brain where color is processed. All light looks the same to rods, the only difference is its intensity. Light that is out of their range of response wavelengths isn't seen anyway.

That's why I say that for true dark adaptation, using a red light prohibits you from doing things like reading and/or taking notes.

I'll second the recommendation for Princeton-tec.

There is a version of the EOS that has a flip up red filter. I have the "bike"version of the EOS and it was bright enough to get me home when my primary bar-mounted light failed. using the lower mode with the red filter should work well for what she is doing. The simple design of the EOS (no external battery packs) seems to appeal to most women I know.

B0wz3r said:

A true night vision red light should be what's called a 'deep' red, in the range of 670 nm or so. This is far enough up the visible spectrum that the cone receptors, specifically the long wavelength or red receptors, will only be activated a very little at this wavelength, and allow true dark adaptation to take place.

When true dark adaptation occurs, the cones are shut down, they don't send any signals to the brain because there isn't enough light to activate them.

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But I thought the point of the the 660-670nm astronomy style lights is that they ARE bright enough, even at that longer wavelength, to keep the red cone cells functioning?

darknessemitter said:

But I thought the point of the the 660-670nm astronomy style lights is that they ARE bright enough, even at that longer wavelength, to keep the red cone cells functioning?

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No, at that wavelength the red cones are activated only very slightly. The point of the deep red is to preserve night vision only, you can't really do much else with it. I think that's the primary reason that so-called 'night vision' lights in the 625 nm range are popular, but they don't really preserve night vision; not so much because of the wavelength, but because they're all too damn bright. Any light, no matter what its wavelength (as long as it's in the visible spectrum), will undo dark adaptation if bright enough. That's why I said the rule is, if you can see the color, it's too bright.



This is a graph that shows the response curves of each kind of receptor; wavelength is on the x-axis, and percentage of maximum possible activation/response is on the y-axis.

That's why I said for tasks that require acuity, and keeping you 'sort-of' dark adapted, the NVG lights are better.

B0wz3r said:

No, at that wavelength the red cones are activated only very slightly. The point of the deep red is to preserve night vision only, you can't really do much else with it. I think that's the primary reason that so-called 'night vision' lights in the 625 nm range are popular, but they don't really preserve night vision; not so much because of the wavelength, but because they're all too damn bright. Any light, no matter what its wavelength (as long as it's in the visible spectrum), will undo dark adaptation if bright enough. That's why I said the rule is, if you can see the color, it's too bright.

That's why I said for tasks that require acuity, and keeping you 'sort-of' dark adapted, the NVG lights are better.

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How will using bluish-green preserve your scotoscopic vision at all? It will bleach the rod cells faster than any other wavelength. At that point you're probably better off using an equally dim white light. The point of using longer wavelengths is to use the cone cells without bleaching the rod cells too quickly. If 660nm is too difficult to work with, then the next logical step would be to try 630nm. Will it start to bleach the rod cells? Yes, but much more slowly than blue-green.

People started refering to bluish-green as "night-vision green" because of uses with military night-vision equipment, not because it has any advantage over other colors for natural human nightvision. Why not just use a dim white light?

darknessemitter said:

People started refering to bluish-green as "night-vision green" because of uses with military night-vision equipment, not because it has any advantage over other colors for natural human nightvision. Why not just use a dim white light?

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I'm aware of why the military started using green; red is too close to IR and anyone who uses red glows like a Christmas tree on an IR sensitive scanner.

The reason to use green instead of white, is because it is so close to the wavelengths that the rods are sensitive to, you need that much less light to be able to have scotopic vision. A dim white light, unless it is truly low enough, which most people don't know about or have lights that are able to provide such a light (even the .2 lumen moon mode on my Quarks is too bright for that, I can still see color when using it).

A white light will activate all the sets of cone receptors, and the brain encodes brightness by the total number of action potentials sent by the retina. So, if you're activating all three sets of cones with a white light, it will appear brighter than a green light. In other words, of two objectively equal intensity lights, one white and one green, the white one will appear brighter because more receptors are being stimulated.

This is also true for red vs. green; about 60% of all cones are red ones, while about 25% are green. As a result, like with green vs. white, of two equal intensity lights, one green and one red, the red one will always appear brighter. So the point is that by using a green light, you can still get better dark adaptation than with even a dim white light.

B0wz3r said:

A white light will activate all the sets of cone receptors, and the brain encodes brightness by the total number of action potentials sent by the retina. So, if you're activating all three sets of cones with a white light, it will appear brighter than a green light. In other words, of two objectively equal intensity lights, one white and one green, the white one will appear brighter because more receptors are being stimulated.

This is also true for red vs. green; about 60% of all cones are red ones, while about 25% are green. As a result, like with green vs. white, of two equal intensity lights, one green and one red, the red one will always appear brighter. So the point is that by using a green light, you can still get better dark adaptation than with even a dim white light.

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But that's the opposite of what you need if you're trying to conserve the rhodopsin in the rod cells. You need light that will stimulate the rod cells the LEAST while still allowing you to utilize the cone cells to see detail in the center of the retina. That way when you switch the light off, the rod cells will recover much faster and allow you to see the very limited ambient light at night (unless of course you're indoors in a room with no windows).

Going back to the original example of reading or taking notes at night, any green or white light that is bright enough to allow the cone cells to see the details of the words on the page is already far too bright for preserving scotoscopic vision. If you try to keep it dim enough to avoid totally depleting the rod cells, it's already too dim to allow the cone cells to see details on the page. There are no rod cells in the center of the retina, and their resolution is too low for reading anyway.

There are certainly many situations where it's better to use dim white (or maybe green), but the original topic involved taking notes at night, where using red light is the best option for simply being able to read and write without harming scotoscopic more than necessary. Ideally the red light should be dimmable, but it will still deplete the rod cells more slowly than a white or green light of comparable output.

darknessemitter said:

But that's the opposite of what you need if you're trying to conserve the rhodopsin in the rod cells. You need light that will stimulate the rod cells the LEAST while still allowing you to utilize the cone cells to see detail in the center of the retina. That way when you switch the light off, the rod cells will recover much faster and allow you to see the very limited ambient light at night (unless of course you're indoors in a room with no windows).

Going back to the original example of reading or taking notes at night, any green or white light that is bright enough to allow the cone cells to see the details of the words on the page is already far too bright for preserving scotoscopic vision. If you try to keep it dim enough to avoid totally depleting the rod cells, it's already too dim to allow the cone cells to see details on the page. There are no rod cells in the center of the retina, and their resolution is too low for reading anyway.

There are certainly many situations where it's better to use dim white (or maybe green), but the original topic involved taking notes at night, where using red light is the best option for simply being able to read and write without harming scotoscopic more than necessary. Ideally the red light should be dimmable, but it will still deplete the rod cells more slowly than a white or green light of comparable output.

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When you activate the cones, the light level must be at least 6x as high as for the rods. At that level, even a low amount of stimulation of the cones is enough to blow out the rods, even if they are responding only very weakly, because they're so much more sensitive than cones are.

As I said, if you can see the color, it's too bright; if you're using a red light and you can see that it's red, you've already blown out your rods. The key is to find the level of light that is just at the photopic/scotopic break point. And for that, a green light can be dimmer than a red light, because of the sensitivity of the rods, and have less effect on the cones as a result.

ANY light that is bright enough to stimulate the cones will saturate the rods; it's that simple.

Sorry about random asterisks, mobile browser thing...

B0wz3r said:

When you activate the cones, the light level must be at least 6x as high as for the rods. At that level, even a low amount of stimulation of the cones is enough to blow out the rods, even if they are responding only very weakly, because they're so much more sensitive than cones are.

As I said, if you can see the color, it's too bright; if you're using a red light and you can see that it's red, you've already blown out your rods. The key is to find the level of light that is just at the photopic/scotopic break point. And for that, a green light can be dimmer than a red light, because of the sensitivity of the rods, and have less effect on the cones as a result.

ANY light that is bright enough to stimulate the cones will saturate the rods; it's that simple.

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But you're missing a couple points. You need the cones in order to read or take notes effectively. Picking green or blue green, colors that the rods are most sensitive to, makes it more difficult to minimize recovery time for the rod cells after turning the light up high enough for the cone cells to function. If you keep blue-green dim enough to preserve scotoscopic vision, you will have a lot of difficulty performing tasks that rely on the cone cells (like reading and note taking).

Thats why red is useful. The rods are less sensitive to it, so you can use a moderately dim red light to utilize the cone cells with less effect on the rod cells than if you used a blue-green light at a bright enough level for the cones to function.