Different led color advantages

i plan on buying a surefire a2 aviator sometime soon and am wondering about the advantages and disadvantages to led colors so i dont pick a bad led color for what i will be using this light for. can someone tell me one of the most common led colors for this light. and could someone recommend a color for me.{i will be using it for backpacking, outdoor illumination, and a bit of military type tasks. i also need to preserve my adapted night vision.} please excuse me if this has been posted before and i should not have posted it again, but please give me some space seeing as i am very new to CPF. i am looking forward to being a part of CPF and the art of flashlights. also about the A2, when you activate the main incandescent light do the leds come on at the same time. and when you twist the tail cap for constant on can you chose between incandescent and leds?

For Night adapted vision Red is very good. I know many astronomers use Red for this very reason. (as long as it is not too bright ) You can read star maps and still keep your night adapted vision for looking through your binoculars or telescope. The rest of your quesions I cannot answer since I have never considered the A2 a light for any of my applications. It is a well regarded light though.

Bill

Bump

Take a look at this page:
http://www.pentagonlight.com/products.cfm?id=1&fig=12&search=starled
They mention what each color is best for.

p1fiend said:

Take a look at this page:
http://www.pentagonlight.com/products.cfm?id=1&fig=12&search=starled
They mention what each color is best for.

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I just love how they call the red light a low signature light that preserves night vision and yet it's rated at 28 lumens. I brought a red photon II to an (astronomical) observatory and was told by several people to "turn off that bright light!". Red light does help with night vision as the human eye is not really receptive to that color but like any color it still has to be dim. Most of the astronomers there used dim white light and the rest used dim red light. The key here being DIM. If you want to preserve dark adapted eyes just dim whatever color you're using and you'll be far better off than using a bright light of any color. FWIW, I discovered (as VT has been telling us for awhile ) that a medium yellow light is an ideal compromise between the red that we're all told we should use at night (and that I find nearly useless) and the white that we all really want to use. It doesn't disrupt NV much more than red but renders objects much more clearly IMO. Just my 2c but for night vision just keep it DIM!

Actually a dim yellow light will disrupt night vision much more than a dim red light. The rhodopsin in your rods (responsible for night vision) respond optimally to yellow-green photons (500-520 nm). The rods are 500-1000 times less sensitive to red photons (600+ nm). With a dim red light, you can still drive your red cones, but minimally effect your rods. So when the lights go off, it's easier to dark-adapt since the rods haven't been affected significantly. Even with a dim yellow light (a level at which you can actually do stuff...like read), I think you would probably be saturating your rods therefore requiring more time for them to recover at lights off. Remember night vision is just that...vision during very, very low light situations (e.g., overcast skies at night with no exterior illumination).

SilentK said:

...about the A2, when you activate the main incandescent light do the leds come on at the same time. and when you twist the tail cap for constant on can you chose between incandescent and leds?

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Yes, yes and yes.

Push the switch in part way, get LED's only.
Push the switch in all the way, get Incan and LED's on.
Twist the tailcap part way, get LED's only.
Twist the tailcap all the way, get Incan and LED's.

Yes, the LED's are always on when the Incan beam is on.

Favorite light of mine (well, that and modded old school L-1's). It really is a truly useful light, although the LED's will be too bright if you are trying to completely preserve your night vision. I would get white LED's.

I don't know if the Chicken has been around lately or if he still makes the Aviatrix rings, but those would turn the A2 into the cat's meow.

SilentK, welcome to CPF!

Questions about the A2 are usually raised in the Incandescent Flashlight section, but I will leave this one here as the A2 is a hybrid light and your question is specifically about the LED color options.

You may however wish to take a look there, as you will find many more threads and discussions about the A2.

Pharbor said:

Actually a dim yellow light will disrupt night vision much more than a dim red light. The rhodopsin in your rods (responsible for night vision) respond optimally to yellow-green photons (500-520 nm).

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500-520nm is blue-green, not yellow-green.



The black line is photopic vision.
The green line is scoptopic vision.

Photopic vision (the cones) responds optimally to yellow-green (555nm).
Scoptopic vision (the rods) responds optimally to blue-green (500nm)

True red light (650nm or longer) has 0 rod sensitivity, but less than 10% cone sensitivity. It also doesn't focus very sharply in the eye, which means I find that I need a lot of red light in order for it to be any good at all -- so much that it will be more likely to disturb others, and bright enough that it may still produce after-images, which can ruin eyesight for astronomy as much as bleached out rods.

Amber light (590nm) is a good tradeoff as rod sensitivity is only a couple percent, but cone sensitivity is about 75%. That wavelength also focuses much more clearly, so I find I can actually see far better with amber light than red light at the same apparent brightness. I've done astronomy on college campuses with copious amounts of stray light from low-pressure sodium lamps (589nm) and surprisingly found my night vision still became adapted fine.

Even with a dim yellow light (a level at which you can actually do stuff...like read), I think you would probably be saturating your rods therefore requiring more time for them to recover at lights off.

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With enough lux to read, even the low rod sensitivity of amber would probably be enough to cause disruption, but that's not the only potential use for flashlights. For example, I may want to look through a bag to find a particular lens, or light up a walkway enough to keep from stumbling with MUCH lower levels of illumination than is necessary for reading. And in those situations, I find amber is a lot more useful in general (for one it reflects off of more stuff than red light does, providing more useful contrast).

Yes, you are correct. 500-520 is more blue-green than green-yellow...I suppose I am still stuck with a physiology mindset (i.e., referring to blue cones as "blue-sensitive cones" instead of "indigo-sensitive cones"). Thanks for correcting that, but the main point was that red light is better at preserving night/scotopic vision. At equal amounts of photons green or red, the green will bleach more rhodopsin than the red.

Pharbor said:

Yes, you are correct. 500-520 is more blue-green than green-yellow...I suppose I am still stuck with a physiology mindset (i.e., referring to blue cones as "blue-sensitive cones" instead of "indigo-sensitive cones"). Thanks for correcting that, but the main point was that red light is better at preserving night/scotopic vision. At equal amounts of photons green or red, the green will bleach more rhodopsin than the red.

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Med student?

I've never heard of rhodopsin but I DO know that I can see much better with my yellow photon than my red and it doesn't hurt my NV too much more. YMMV

You might find this article interesting: http://www.flashlightreviews.com/qa/monochrome.htm

cv3po said:

Med student?

I've never heard of rhodopsin but I DO know that I can see much better with my yellow photon than my red and it doesn't hurt my NV too much more. YMMV

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Rhodopsin is the visual pigment in the rods...the actual molecule that absorbs a photon during the visual process. At the level that we're discussing (trying to determine what color light best preserves night vision) it's probably too subjective. There's really no way of calibrating how much yellow versus red light you're using, or how quickly you dark-adapt after either exposure when the light is turned off. But from a purely biological standpoint, a yellow light will bleach more of the rhodopsin in your rods than the same amount of red light. Once the rhodopsin in your rods (or cone pigment in cones) is bleached, it has to be regenerated through a biochemical process. Only a small percentage of the rod's visual pigment needs to be bleached for the cell's response to saturate, rendering the rod useless until it recovers. Since the same amount of red light bleaches far fewer rhodopsins, it would take the rods a shorter amount of time to recover. That's the reason why people suggest red light to preserve night/rod vision.

That being said...everyone should pick whatever color light he/she thinks works best for them.

Good article btw JNewell!

Pharbor said:

Rhodopsin is the visual pigment in the rods...the actual molecule that absorbs a photon during the visual process. At the level that we're discussing (trying to determine what color light best preserves night vision) it's probably too subjective. There's really no way of calibrating how much yellow versus red light you're using, or how quickly you dark-adapt after either exposure when the light is turned off. But from a purely biological standpoint, a yellow light will bleach more of the rhodopsin in your rods than the same amount of red light. Once the rhodopsin in your rods (or cone pigment in cones) is bleached, it has to be regenerated through a biochemical process. Only a small percentage of the rod's visual pigment needs to be bleached for the cell's response to saturate, rendering the rod useless until it recovers. Since the same amount of red light bleaches far fewer rhodopsins, it would take the rods a shorter amount of time to recover. That's the reason why people suggest red light to preserve night/rod vision.

That being said...everyone should pick whatever color light he/she thinks works best for them.

Good article btw JNewell!

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wow i would like to say that i realy appreciate you guys in helping me with my search for a geat led color. i have decided to go with white just because of the fact that i have played around with my friends different led colored lights {cheap things} yesterday and found out that my eyes and i dont like that i cant tell one color from another with anything but white. and with hearing that it is how dim the light is that plays an important role with night vision. besides i plan on sticking to the CPF spirit by owning more than one A2 Aviator!:twothumbs so i can get another color. i want to thank you guys for your help!

Unless you're doing a special job. I think a white LED is the most accurate "real light" as you can get.

Meaning you see the real colors of the objects under the LED light.

Photon Freedom Micro Keychain Microlight - Many Colors Available!
http://batteryjunction.com/phfrmipesafl.html

Beam color characteristics:

Red.

Red is favored by pilots, sailors, fishermen, and astronomers for the excellent ability to preserve night vision and also for uses of safety, signaling, and map reading. Red is an internationally recognized attention color. 630 nm.

Yellow.

Yellow is a traditional flashlight beam color, with good projection - up to 20 to 30 feet. Because the red, yellow, & orange Photons use a single CR2032 battery rather than the pair of smaller CR2016 cells used in the other colors, they will provide a significantly longer battery life at the expense of some brightness. This makes these colors excellent for use in emergency kits or other situations where battery life is a primary concern over absolute brightness. 592 nm.

Orange.

The orange beam combines some of the aspects of both the red and the yellow. It doesn't disturb night vision as much as the yellow, yet will illuminate a path better than the red. 605 nm.

Green.

The green light is nearly as bright as the blue, turquoise, and white lights while offering a slightly longer battery life. Because the green LED bulb tends to be a bit more efficient than the other colors, it can run for up to 20 hours with one set of batteries. 525 nm.

Blue.

The blue beam is tremendously bright and makes an excellent all-around flashlight. The wide-angle bulb illuminates everything to the side as well as forward. 470 nm.

Turquoise ("Night-Vision NV Green").

Because of it's lighter shade of color, the turquoise beam is arguably slightly brighter than the blue. The wide-angle bulb can light up an entire room. At reduced brightness levels (try swapping a single CR2032 for the included pair of CR2016 batteries), the blue-green color of the turquoise is an excellent alternative to red for night vision preservation. 495 nm.

White.

Now with the Nichia DS LED! 2-4X the brightness of similar LED's! (white Freedom Micro only), the white is now hands-down the brightest of beam colors, a full 2-4X brighter than just about every other single-LED keychain-sized flashlight on the market! White is great for all around use as everything is viewed in full color. The narrow-angle bulb produces an incredibly bright -- and practical -- flashlight-style beam. 6500 K.

Purple.

The purple light produces a black-light effect, making lighter colors (whites, fluorescents, etc.) appear to glow. Purple bulbs do emit some UV light, which can be harmful if viewed directly. 405 nm.

I've had, at one time or another, A2's with every color. For my eyes, the single best color is YG. It preserves colors to a much greater extent than the other colors. There's a post somewhere that has pictures of a map that demonstrate this well. But for absolute low-level, and total preservation of night vision, red is better. It's just not as functional in most situations. Even though the YG is rated at the same or lower lumens, it appears much brighter than the red.

davidra said:

Even though the YG is rated at the same or lower lumens, it appears much brighter than the red.

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The lumen scale is based on center of field-of-vision, at high levels of illumination. At high levels of illumination (lux) both should appear the same. However, as very low levels of intensity, sensitivity of your eyes "shifts" toward the blue end of the spectrum. It's not a binary switch from photopic vision , to night vision, but more of a gradual transition. This "hybrid" mode so to speak is called mesopic vision, and is the mode that your eyes operate in in relatively dim, but not "pitch black" conditions, such as full moon, or twilight conditions. The "strategic" use of flashlights at real dim levels takes advantage of this mesopic vision, and while it doesn't preserve night vision at levels sufficient for astronomy, for general purpose outdoor use it does take advantage of your night vision without completely wiping it out.

For example, I have taken red, green, and blue LEDs that appeared to be the same intensity viewed side-by-side in a lit room, and used them for ceiling bounce. In that situation, the red was nearly invisible, the green was the most useful (gave the best contrast) and the blue appearaed the brightest, but provided poorer contrast than the green.

Other reasons why the YG might "appear brighter" is that many more things will reflect yellow-green light than red light, for example grass will reflect YG almost 100%, and absorb red almost 100%. Finally, the focal length of the eye is optimized for YG light, so it should focus on the retina most clearly (~555nm is dead center in the visual spectrum), meaning less light will be needed to say read fine print, or peform other tasks requirign black/white contrast.