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There has been some discussion in various newsgroups (aviation, rec, astro) regarding what color is best for night vision.  In particular, the assertion has been made that the Air Force is switching to blue-green, and that red is passe.  Here is  what the applicable military specification has to say.

MIL-1472D General Requirements  Display illumination and light distribution.  Display illumination. Normal. When maximum dark adaptation is not required, low brightness white light (preferably integral and adjustable as appropriate) shall be used; however, when complete dark adaptation is required, low luminance [0.07 - 0.35 cd/m(2) (0.02 - 0.01 fL)] red light (greater than 620 nm) shall be provided.
Condition of UseLighting Technique (*)Brightness of Markings cd/m2 (Ft-L) Brightness Adjustment
Indicator reading, dark adaptation necessaryRed flood, indirect or both, with operator choice0.07-0.35 (0.02-0.1) Continuous throught range
Panel monitoring, dark adaptation necessaryRed edge lighting, red or white flood or both, with operator choice0.07-3.5 (0.02-1.0) Continuous throughout range
Chart reading, dark adaptation necessaryRed or white flood with operator choice0.35-3.5 (0.1-1.0) Continuous throughout range

(*) Where detection of ground vehicles or other protected assets by image intensifier night vision devices must be minimized, blue-green light (incandescent filament through a filter which passes only wavelengths shorter than 600 mm) should be used in lieu of red light.

The answer is red is best for night vision.  Use of blue-green is to protect night vision goggles, not unaided night vision!  Most red filtered incandescent bulbs emit red and a lot of infra-red and therefore are easily visible in night vision goggles and would overload night vision goggles in the cockpit.  Night vision goggles are not very sensitive in the blue-green part of the spectrum because they use blue-green cutoff filters.  That's why blue-green is used in the cockpit.  The military has split the spectrum giving blue-green to the unaided vision and yellow through infra-red to night vision goggles.  MIL-STD 1472 makes another point -- adjustability -- one should be able to adjust the brightness to match the need.Mr. Brian Skiff (We are crediting Mr. Skiff for the information, we in no way  imply that Mr. Skiff endorses our products) posted some additional background to sci.astro.amateur in April 1997;
 "... it's been well-tested under laboratory conditions.  See the following papers, all of which were published 40 years ago in the "Journal of the Optical Society of America":Hulburt, 1951, "Time of Dark Adaptation After Stimulation by Various Brightnesses and Colors, "  Journ. Optical Soc. America (JOSA), 41, 402.
Smith et al., 1955, "Effects of Exposure to Various Red Lights upon Dark Adaptation Measured by the Method of Constant Stimuli," JOSA 45, 5.

Kinney 1955, "Sensitivity of the Eye to Spectral Radiation at Scotopic and Mesopic intensity Levels," JOSA, 45, 507.

Sweeney et al. 1960, "Season Changes in Scotopic Sensitivity," JOSA 50, 237.The first two papers show quite clearly that the
redder the better for getting re-dark adapted after exposure to light.  The bottom line of these papers is that red lights are best, but if you can see that itís red on the paper you look at, then it's too bright.  You see people at star parties with blazing bright flashlights and light boxes for reading charts, thinking that since they're red itís okay.  But if the red light you're using shows any more colorfully than funny brown-grey, then it's too bright."
And this last point is a key point -- regardless of color, if its bright enough to dazzle your eyes, it will affect your night vision -- hence adjustability as per MIL-STD 1472. So for most of us, the answer is red and adjustable brightness  for preserving night vision.Preserving night vision is distinct  from visual acquity.  If all one is doing is picking up an eyepiece, checking some equipment, walking around,  glancing at a control, any task that doesnít require high visual acquity, then adjustable brightness red light is best for preserving night vision.If one wishes to read fine details that requires visual acquity, that requires using oneís foveas which are packed with cones (color sensitive retinal cells),.  Then adjustable brightness white is a is a perfect choice for sharper vision and shows colored markings on charts correctly.
For civilian users:
Starlite with 2 red LEDs is the perfect flashlight for astronomy.
Skylite switchable between 2 red and 2 white LEDs is the perfect for civil aviation.
Moonlite with 2 white LEDS is the perfect a general purpose outdoors flashlight.

For military night vision goggle compatibility

Mil-Skylite switchable between 2 green and 2 white LEDs
Mil-Infralite switchable between 2 green and 2 infra-red LEDs.

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