Genzod
Banned
- Joined
- Apr 25, 2017
- Messages
- 392
What is the minimum amount of lux required to marginally identify a 2x6" Appalachian Trail white blaze marker at 100 meters?
SOLVED: This post poses a question that is ultimately answered in an experiment documented at this post. Not only that, the amount of intensity required at any distance is resolved.
A useful interactive plot is derived there and is used as a tool to solve some problems with light and naked eye target identification here and here.
A forum member brings up the need for scopes for small targets (which isn't necessarily always true as I later proved). Others attempted to use unsound arguments, based mostly in a failure to understand the context of my question, to dismiss any and all hope for ever finding a practical answer to this question.
The math for the scope problem was demystified at this post and several scoping examples are provided here. The triumph of this effort discovers a general formulaic solution adaptable for almost anyone's eyes here.
But it's fun to first read the question, watch a small gaggle of obvious reading comprehension failures and irrational attempts determined to "block that kick" and talk me out of finding a practically useful solution. So pay attention, try to get the context, resist the urge to become narcissistically dismissive and intellectually condescending, and try to have some fun. But not too much fun because that would be X-rated!
Purpose:
I'm a fastpacker who enjoys running at night on the Appalachian Trail. I'm replacing my defective headlamp, and I'd like to choose one with enough throw to identify navigational white blaze tree markers at a distance, preferably with a 100 meter constraint for marginally identifying such a marker under ideal nighttime conditions and still have enough foreground spill light for running under technical trail conditions. (Later, I would realize the need for lamp redundancy, so I decided to separate tasks--headlamp for running and a more powerful handheld for marker identification).
But carrying a lot of weight is not expedient for a fastpacker running up mountain inclines, and lamps increase with weight as their performance improves. Therefore, I need to know the minimum amount of light I can get away with so as to keep weight at a minimum. I'm on a budget here, and I can't just buy several $80 lamps and try them out to see what works best. If you aren't on a budget and own Fort Knox, lucky you.
Question:
What is the minimum RECEIVED lux at target (as opposed to REFLECTED lux) required to discern the white blaze target on the tree in photo above? I'm assuming 0.25 lux throw is just a standard used for calculating flashlight range for comparison's sake, not for what most people actually need to recognize a target at a specified distance.
(Did you stop reading here, go to the photo and answer the question? What's the matter with you? Don't you like to be entertained?)
If you need to qualify your answer as a range of distances (for example: "4-8 lux instead of something like "about 10 lux") that's fine, just help me understand why you chose those bounds as an answer. Aw shucks, explain why you chose your answer anyway so I can research it and get a gist for exactly how much fertilizer is in your shed.
Yes, that kind of fertilizer.
Actually, I like smart people. I like to check their answers, so I can know who to like.
Everyone else...
NO BOOZE FOR YOU! :drunk:
What, you don't drink? Okay...
NO FISH STICKS FOR YOU!
Given/Assumptions: (PAY ATTENTION!)
Target is as appears in photo above, a 2" x 6" painted white blaze marker placed about 2 meters high on a highly contrasted tree. Assume this is a magic tree and all the trees with white blazes look like this. I like simple things.
Target is 100 meters from searcher in direct line of sight and is anticipated to be on a tree next to a well worn path. (109.4 yards for you Americans who think the metric system is a communist plot designed to confuse the world).
Searcher is old, American and speaks in two measurement systems, but has healthy night vision, which is corrected with glasses but due for a prescription renewal (later learned this was the legal limit for driving of 20/40 at the time I collected my data).
Atmosphere is clear--no precipitation, humidity, fog or Skittles. (Taste the rainbow).
There is no ambient light (edit: or foreground spill) whatsoever. This is not a university graduate level question. Stop making it complicated!
I'm the only person on earth with a flashlight (a magic flashlight) , and no, you can't borrow it.
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