I'm reminded that manufacturers' numbers as to throw distance are wildly biased in favor of yielding artifically inflated distance claims. Recall that manufacturers' standard throw calculation is based on delivering 0.25 lumens on target. At any meaningful distance, unaided human vision is not capable of detecting minimal candela and lumens on the target, mostly because of the effects of the inverse square law of electromagnetic energy propagation (the light intensity diminishes as the invesrse square of the distance the light travels). The limited intensity of light illuminating a traget at "X" distance will be ridiculously less after said the reflected light makes the return journey to your eyeballs.
The basic formula is Intensity of Light = 1 / Distance². [I'm writing this next part after midnoght and from memory, so I invide anyone who wants to correct my math to do so; gently of course, and without flaming me, if you would be so kind.]
For example a 1000 lumen light at 10,000 candela, measured at one meter will put 1000 lumens on target at 10,000 candela. (Ignore the various losses from absorbtion and reflection for the moment, and assume the light delivers 10,000 OTF candela.) Assuming the thing you want to illuminate is non-reflective (a coyote or some other non-reflective critter) you'll need a minimum of at least 0.1 candela of difference in illumination between the target and the background to come back to your eyeball in order to differentiate the target from the background. (At that low level of differentiation you won't be able to identify any detail, only distinguish a thing from the background...you still worn't know if it's a coyote, a dog or a racoon, but you'll at least know it's not a bear.) A 10,000 candela light source hitting a surface (e.g.- coyote fur) at 100 meters will put roughly 10 candela on target. The non-reflective fur of your target animal will therefore start it's return to your eyeball at 10 candela, and fall off from as the inverse square of the distance from our coyote back to your eyes, where you'll be treated to light with the blazing intensity of 0.0001 candela.
Pop Quiz: Just how well do you think you're going to see that target?
I've found that as a general rule of thumb, a manufacturer's claimed throw distance as measured in meters can be used to estimate how well you'll be able to see the thing being illuminated if you substitute "feet" for meters. So a claimed throw of 365 meters translates as a distance of about 365 feet as the distance at which I'll be able to see the thing being illuminated (at best), and likely somewhat less if the target is a dark, non-reflective surface.
So, does your real world experience mirror mine? If you live in an urban area, do hard surfaced urban environments (sidewalks, buildings, etc.) allow greater surface reflectivity, thereby enabling greater visibility distances? I feel this might be a worthwhile discussion.
Finally, and in clarification, I'm writing about the distance I can see things illuminated by my light, and not the distance at which someone else can see my light (an example of which would be the distance at which a search and rescue pilot could see the SOS signal from my torch).
Comments?
