chevrofreak
Member
If the mask moves it increases the chance of point-of-impact shift when reticles are changed.
Why "Red" Dots?: Just fun discussion...
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HankB
Member
Red LEDs are cheaper than other colors, so they're preferred for reticle illumination by the manufacturers.
Moreover, red light tends to preserve night vision - blue does not.
Blue is not the most visible color, and the human eye's performance isn't peaked at the blue end of the spectrum. Note that the "yellow" or "amber" shooting glasses used by some bullseye competitors block blue, which sharpens image contrast.
Moreover, red light tends to preserve night vision - blue does not.
Blue is not the most visible color, and the human eye's performance isn't peaked at the blue end of the spectrum. Note that the "yellow" or "amber" shooting glasses used by some bullseye competitors block blue, which sharpens image contrast.
Hank, are you sure about that?
In the 80's, early 90's my Army unit stopped using red lights at night because the red light was washing out the red and brown markings on our maps. We switched to dim blue lights, and I never noticed a degradation in our night vision retention.
LawDog
In the 80's, early 90's my Army unit stopped using red lights at night because the red light was washing out the red and brown markings on our maps. We switched to dim blue lights, and I never noticed a degradation in our night vision retention.
LawDog
WayneConrad
Member
I think Kor's got it.
Most things you might need to shoot (and most of the places they hide) aren't red, so red will show up well against them.
Most things you might need to shoot (and most of the places they hide) aren't red, so red will show up well against them.
HankB
Member
LawDog,
If you look at graphs of photopic vs. scotopic vision, you'll see why red light is preferred for dark adaptation. Photopic sensitivity is centered in the mid-550nm wavelength band, while peak spectral sensitivity for scotopic vision (which predominates for the dark-adapted eye) is shifted towards the blue, peaking at about 510nm. This "Purkinje Shift" comes from the differing spectral sensitivities of the rods and cones in the retina.
Blue light will still be activating the rods, which you need to see in the dark, so they won't "dark adapt" as well as they would in complete darkness. But the rods are MUCH less sensitive to light in the red part of the spectrum, so in red light, the rods react almost as if they were in complete darkness, and so they adapt better.
As for shifting from red light to blue to read maps - well, if all you've got is red light to look at color maps, then all you'll see are shades of red, so some markings will wash out. Shifting to dim blue light will restore some of the contrast, making red markings look blacker . . . and as long as the light is dim, it won't affect night vision too much.
On the other hand, visual acuity is affected by color as well. The eye has about 1.5 diopters of chromatic aberration. Normally, visual acuity is given for white light, but for monochromatic yellow and yellow-green light, it actually improves a bit. (Yellow shooting glasses, anyone?) Visual acuity is just slightly lower for red light, but in blue or FAR red light, visual acuity is down by 10%-20%.
Some of this is discussed in the book Modern Optical Engineering by Warren J. Smith.
If you look at graphs of photopic vs. scotopic vision, you'll see why red light is preferred for dark adaptation. Photopic sensitivity is centered in the mid-550nm wavelength band, while peak spectral sensitivity for scotopic vision (which predominates for the dark-adapted eye) is shifted towards the blue, peaking at about 510nm. This "Purkinje Shift" comes from the differing spectral sensitivities of the rods and cones in the retina.
Blue light will still be activating the rods, which you need to see in the dark, so they won't "dark adapt" as well as they would in complete darkness. But the rods are MUCH less sensitive to light in the red part of the spectrum, so in red light, the rods react almost as if they were in complete darkness, and so they adapt better.
As for shifting from red light to blue to read maps - well, if all you've got is red light to look at color maps, then all you'll see are shades of red, so some markings will wash out. Shifting to dim blue light will restore some of the contrast, making red markings look blacker . . . and as long as the light is dim, it won't affect night vision too much.
On the other hand, visual acuity is affected by color as well. The eye has about 1.5 diopters of chromatic aberration. Normally, visual acuity is given for white light, but for monochromatic yellow and yellow-green light, it actually improves a bit. (Yellow shooting glasses, anyone?) Visual acuity is just slightly lower for red light, but in blue or FAR red light, visual acuity is down by 10%-20%.
Some of this is discussed in the book Modern Optical Engineering by Warren J. Smith.
gulogulo1970
Member
OK I'm going to take a shot at explaining the blue light being stronger than the others.
If you are in a black lightless plain and have flashlights of varying colors, the blue light would travel further and be seen by other people at a further distance.
I believe and could be wrong on this next one, that this is the reason the sky is blue and not red or yellow. The stray light that makes it the farthest through the atmosphere is blue so the sky is blue.
If you are in a black lightless plain and have flashlights of varying colors, the blue light would travel further and be seen by other people at a further distance.
I believe and could be wrong on this next one, that this is the reason the sky is blue and not red or yellow. The stray light that makes it the farthest through the atmosphere is blue so the sky is blue.
fletcher
Member
As mentioned by others, the reason is definitely technology. Effective diodes that emit colors such as green (real green, like in those stoplights) and blue light are relatively new, and may not be cheap to produce in relatively small quantities such as for dot sights.
Blue light is "stronger" because it is higher energy.
The sky is blue because blue light is scattered in the atmosphere.
Blue light is "stronger" because it is higher energy.
The sky is blue because blue light is scattered in the atmosphere.
The peak of color sensitivity is in the green area. As noted, red has the least effect on rods to preserve black/white (night) vision.
The green sensitivity was exploited for many years in darkroom filters for handling color material. It is possible to make a green light dim enough to see by but not intense enough to affect film (this also plays on the varying sensitivity of the film).
Green light plus red light is yellow. Two color LEDs have been around for a while now, and by adjusting the mix of on time for the LEDs you can produce a smooth transition from red through orange to yellow then into green (there are sickly green-yellow combinations I skipped since no one uses them).
Some of the bi-color LEDs had only two leads, so polarity is used to light the separate colors. Alternate them quickly (faster than about 25 Hz) and you see a single color. If you move your eyes while looking carefully at the LED you can sometime see the separate red and green.
There are tri-color (Red-Green-Blue) LEDs available now. You can make every color in the rainbow.
The makers of red dot sites are probably using a standard LED from some manufacturer. Custom parts demand a very large volume to be practical, millions of pieces for something as cheap as an LED.
The green sensitivity was exploited for many years in darkroom filters for handling color material. It is possible to make a green light dim enough to see by but not intense enough to affect film (this also plays on the varying sensitivity of the film).
Green light plus red light is yellow. Two color LEDs have been around for a while now, and by adjusting the mix of on time for the LEDs you can produce a smooth transition from red through orange to yellow then into green (there are sickly green-yellow combinations I skipped since no one uses them).
Some of the bi-color LEDs had only two leads, so polarity is used to light the separate colors. Alternate them quickly (faster than about 25 Hz) and you see a single color. If you move your eyes while looking carefully at the LED you can sometime see the separate red and green.
There are tri-color (Red-Green-Blue) LEDs available now. You can make every color in the rainbow.
The makers of red dot sites are probably using a standard LED from some manufacturer. Custom parts demand a very large volume to be practical, millions of pieces for something as cheap as an LED.
entropy
Member
Loose Grouper, the M16A2 uses a racheting pawl with three teeth for it's three round burst. 
Hank B is onto it here; more correctly, red light diminishes night vision less than blue. Oddly enough, the screens on NVD's are all green.
Hank B is onto it here; more correctly, red light diminishes night vision less than blue. Oddly enough, the screens on NVD's are all green.
GigaBuist
Member
Since I have nothing to add to the actual topic, as it seems folks know more about the eye than I do, I'll add to this:
Blood. Blood == Danger.
Its a primal thing that makes us label dangerous materials with red labels and such.
Now... back to the show.
As others stated, red does not occur in nature that often. Where do you see red in nature most often?
Blood. Blood == Danger.
Its a primal thing that makes us label dangerous materials with red labels and such.
Now... back to the show.
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