Qucik question: Which protect night vision best: Red or Blue light in torches , errr flashlights. There seems to be a cross Atlantic diference here, not just in what we call them but in what colour they should be. UK Books talk about red, I've noticed Americans talk about blue.<br><br>Justin<br><br>ps in another thread there's talk of Fanny packs, over here that could get you in a bit of bother since we call them Bum Bags, the word fanny is reserved for a rather different anatomical feature belonging to women.

Red light protects night vision. Blue is used by the military to not infterfere witht he use of night vision goggles that are less sensitive to blue light.<br>Blue does not protect night vision.

You could also use blue (and yellow) for places where there is a lot of smoke.

Thanks Beachdoc<br><br>You've saved me a few pounds! Sometimes a red filtered torch comes in handy when out badger watching at night.<br><br>Justin

Justin,<br><br>...and don't forget green, as it enters the debate now. Personally, I'm a "red light" afficiondo, which makes me an antidiluvian these days, I think.<br><br>I'd like to read a authoritative contemporary research paper on the topic. Much of the recent "info" that I have read does not seem to directly address the visual purple washout problem (which is why red light was first favored). Instead, the articles I have seen talk about "dazzle" (intensity), which is a whole 'nother topic - that's a mechanical (iris) aspect. Too bright a light of any visible color will cause the pupil to contract, of course. IMHO, the major mis-direction comes from our current fascination with monochromatic LEDs that can be rather intense if the LED proper is viewed.<br><br>My pupils re-dialate very rapidly; visual purple takes quite some time (average 20 minutes for most folks) to recover. I experimented with a red photon II in January this year and found it easy to dazzle myself with it BUT my night vision was not affected - when I stopped shining the light in my eyes, I could see in low ambient light within a few seconds. A filter-equipped mini-mag flashlight did not dazzle me as badly as the LED. A better test will be to have an observer note my pupil size, but I didn't think of that at the time.<br><br>I have been skeptical of the efficacy of blue for preserving night vision. My experiences with blue vs red came late in my Army career. I found that blue washed me out a little - not as bad (totally) as "white" light, but noticible to me. Red does not adversly affect my night vision. At that time, the lamps were incandescent and the color was established by a filter. Where I was, I am certain who advocated the blue vs red and am certain why they did - it had a lot to do with distinguishing certain colors and little to do with preserving night vision - sort of a sop, at the time, to not using white light. However, there may be some merit to the blue - surely it is better than white light. My observations were hardly scientific. And monchromatic blue light from LED sources may have less adverse effect than the multi-spectral light from filtered incandescents. As I wrote, I'd like to read a good research paper on the topic - one that deals with both night vision (visual purple) and dazzle (iris).<br><br>I think Chris K. may be an advocate of blue light - Chris, will you chime in here with your experiences, please?<br><br>Regards,<br><br>Tom

Makes sense - NVGs are very sensitive at the red end of the spectrum - which is why the built-in invisible illuminator is an IR LED. Thanks; I hadn't thought of that.

Well... Blue interferes the least, but enough of it will still white-out NVDs. Voice of experince, but with genII commie-ware.<br><br>I was told that the other reason for blue is, how many of us have seen a blue muzle flash. Red, white and amber could look like gunfire, while all but the most trigger happy, paranoid person would not make that mistake. In theory. It may also have to do with blue light traveling less than others, so it's not as noticable from the air. <br><br>That's just what I've been told.

incandescent filter vs. monochromatic LEDs <br><br>I saw Beach Doc's reply, which give a simple explanation on red vs. blue. But your reply made me wonder if there's any significant difference between the light source for either color. My guess would be that red or blue from any source would have to have similar wave lengths, otherwise they'd be different colors altogether, and that the sole difference would be intensity. This may explain the difference in the dazzle effect as the filter will reduce the intensity of the light source as photons from the non-red spectrum are blocked, where as the LED generates the photons at the red spectrum wavelength and all are emitted. At least that's my layman's guess (which could be very wrong ).<br><br>Also, isn't the reason red results in better nightvission is that the rods in the eye are more sensitive to photons from those wavelengths?

My experience is anecdotal. Blue light supposedly washes out under moonlight if remaining unobserved is an issue. I have also been told a flashing or strobe effect with blue may induce an epileptic seisure. Doug's article is still timely on the subject. The Watkin's Aviation website lists a splendid unit with mutliple filters ( no assembly required!) much like a small maglight. I go for redundancy in lights ( and color) much like firestarting. The caveat ( especially for those with ageing eyes) to go slow at night, or if possible just stay put is wise advice, under any color 8O)

HI Justin,<br><br>A couple of thing to consider with colored lights is the effect on things you are looking at. If you are using a red light, red objects become invisible. Try this get out a deck of cards, turn off the lights, turn on your red light and try to play cards. You will be able to see you spade and club cards but your heart and diamond cards will look as if they are blank. Just something to remember. <br><br>Also red LEDs are the most energy efficient. Batteries in a red LED flash light can last days longer than white or blue. While colored lenses are no more efficient than clear lenses. <br><br>David Koelzer<br>