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Modern flashlights have brightness up to several thousand lumens which is great. However it's not clear how bright a flashlight I might realistically need.

Suppose I want to go on a search party such as for example when a person is lost in the terrain and police and volunteers move through the terrain and try to find that person.

How bright of a flashlight would be reasonable for such scenario?

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I just asked all the search-and-rescue people I know and they all said that night searches are rare, because they are dangerous. They also said they don't have standard equipment. Mostly, people just grab some 200-lumen head lamps and hope for the best. – theJollySin Sep 5 '13 at 16:27
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@theJollySin - I asked my SAR mates and they said the same. They do have huge lights on the vehicles/helicopters though, and they all rate the LED Lenser torches. – Rory Alsop Sep 5 '13 at 17:08
    
I've been on enough night searches to warrant having really bright flashlights. That being said, most of them we were on track for someone very recently missing, so deploying at night was justified. I'd rather be called in to search at night than called days later when tracks are obliterated and chances of a rescue are less likely than a recovery. Safety isn't usually an issue as we train and equip for both night and day searches. – Nathan Paul Simons Apr 5 at 23:15

For search party purposes, bigger is almost always better, both from the perspective of the lost individual - he/she may be able to see the light from a distance and make themselves more visible or move towards the light, and from the searcher trying to see their target, perhaps an unconscious individual - spotting clothing or non-natural material is much easier with a very bright light.

For this reason pretty much all search teams carry high intensity floodlights. This is a portable, high intensity torch rated at 1100 lumens:

enter image description here

But that may be impractical for a light team already out in the field, so SAR teams recommend head torches like these. Only 170 lumens, but very portable:

enter image description here

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Okay, so will brightness around one thousand lumens be enough for most cases? – sharptooth Sep 6 '13 at 12:59
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I would imagine so, yes. – Rory Alsop Sep 6 '13 at 13:44
    
Equally (if not more) important as lumens is output regulation. A regulated output will put out (approximately) the same brightness for the duration of the battery life. An unregulated light will quickly drop in output until it's hardly useful. Always get a regulated light if you can. – nhinkle Aug 14 '14 at 20:56

I'd think that it will depend very much on what you search for:

  • do you expect the person to respond, e.g. put up whatever scrap of reflective material they have with them when they see your search-light?
    In that case, and open landscape a highly brilliant lamp would be good: you could sweep a large space slowly with such a light and look for reflections.
    E.g. I can see the reflective background in the eyes of the neighbour's horses across the valley (ca. 800 m, 1100 lumen light IIRC) without problem. You could similarly detect reflective material.

  • Do you have to seach in bushes where you anyways cannot see far?
    In that case, less brilliant but wide angle is probably better (but I'd guess that chances are pretty small to accomplish much before the next morning). Brilliant and tightly focused light in such a situation will possibly be more of a hindrance than a help: it can easily blind you enough to see nothing at all outside the narrow illuminated space, and even in the direction of the search light nothing but the bushes in the foreground.
    I guess the most sensible thing would be to try covering easily accessible and sensible places rather than going right through the bushes during the night: along roads/trails where the lost person is likely to be and where your light can actually help. If you can expect the person to be responsive, then acoustics may be your friend - better if organized: shout / whistle in a concerted fashion, then stop to listen.

  • Are you looking for someone who is hiding or unable to respond and cannot be expected to have anything reflective on him? You really need to search through the bushes?
    Then, maybe night vision gear would be better than search lights. Or search dogs. If you have to do with lamps, you'll need a massive group helping with the search to cover a decent area in one night.

I think that headlamps, torches and rescue lights (e.g. head lights of fire fighter trucks) are optimized towards a very different purpose: they are optimized to brightly illuminate a restricted space. Head lamps e.g. are useful to enable you to work, e.g. repair something or care about an injured person. But even though mounted on your head, I find them illuminating an uncomfortably small angle for e.g. hiking or in a cave. The torch I mentioned above is also good if you want to repair something, but it is useless if you want to search in bush terrain.

I find that head lamps are often a pain for a group: most people are polite enough to look into your face when speaking or being spoken to. Which will blind away your dark adaption over and over again...

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With regards to searching or SAR, I think @Rory Alsop, hit the nail on the head. You really want a brighter and wider field of light when searching for someone. However, as an avid backpacker, you don't need that many lumens. So... if you are searching for a path or night hiking, I use a 70 lumen headlamp that has worked fantastically well and when I need to 'search' a bit further, I use a 100 lumen flash light. With that amount of light, you are able to see the reflections of the trail markers on the tree. Hope this helps!

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Unfortunately the regions where I trek, there are no trail markers :D – Unsung Sep 27 '13 at 6:26

If you decide on something really bright, check out scuba diving lights. They are made extra tough, extra bright and are waterproof. And, you want to carry two: One bright one for searching and a smaller one for reading something, examining a person for injuries, etc. You also want the smaller one as a backup just in case something happens to the larger one.

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Scuba lights may not be a good choice because they're designed to be used underwater and thus be water cooled... so the light may overheat if used at max output with only air cooling. – nhinkle Apr 6 at 1:09

For serious organised search and rescue there is an argument that you want as much light over as wide an area as you can possibly get as this maximises your field of vision and reduces the area of ground you need to cover on foot.

there is also the consideration that a bright light is more likely to pick up a flash of reflective tape etc on a casualty's gear.

However there is a counter argument that unidirectional artificial light will never realistically give you the same visual acuity as daylight and at night a bright torch can produce tunnel vision where you only concentrate on the illuminated cone and can ignore more subtle clues from your peripheral vision or other senses.

Similarly if you are searching for a casualty who is using a small torch or chemical light to signal then a very bright light may actually impede your ability to spot them.

Clearly there are different situations, for example between a small group searching a hillside for a lost hiker vs a long line of people combing a wood for a lost child.

There is also the consideration that for a serious search at night on open ground an aircraft with thermal imaging equipment will have the large area/long range aspect covered far better than any search on foot so a foot search may be more concerned with short range vision in dense cover (woods, buildings etc) where light output is less important.

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It depends on what exactly you're talking about:

  • Searching, not tracking, you will probably want the brightest thing you can get. Of course, there are still factors that go into this (are you on foot having to carry the weight, can you run it off a vehicle power supply, etc). That being said, I've been on a search at night in the Mt. Whitney region (off trail, very rough class 3/4 brush choked terrain) where my Fenix PD35 UE (1800 lumens) was adequate, but it was also nice that another teammate had a Fenix TK75 (4000 lumens), but that one is also much heavier and bulkier. The PD35 is also my favorite for bouldering past sunset - you can really see the details on the rock.
  • Tracking, you might not want the brightest, or at least you want to be able to turn down the intensity. Again, it depends on more factors (night versus day tracking). I recently upgraded from a Fenix P1D (180 lumens) to a PD35 TAC (1000 lumens) for two reasons: use during daytime tracking, and it's much easier to click a button than twist the head when it's attached to the bottom of my trekking pole. The medium level (200 lumens) is still good for night time tracking, but on overcast days you want all the power you can get to really bring out the edges in tracks.
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