Candelas to throw cheat sheet

I made a little Octave script to calculate the throw (m) of a flashlight from intensity (cd@1m) for various lux levels. The script produces the following graph:

If you're interested in the throw defined by the ANSI stantard, follow the red line (0.25 lux). Other levels are added for those interested in more higher level of illuminance.

You can find the scrip file here: throw.m. I don't have MatLab and I'm beginner with the Octave too so I cannot guarantee that the script will work in ML.

Confirms what I always thought. . . . Take the manufacturer's spec for throw, and reduce it by 50% to get a number for real (usable) illumination.

wjv said:

Confirms what I always thought. . . . Take the manufacturer's spec for throw, and reduce it by 50% to get a number for real (usable) illumination.

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Indeed. I checked the Wikipedia and it says full moon on a clear night is 0.27–1.0 lux. The ANSI FL1 Beam Distance (to 0.25lux) is wrong in that sense giving you much longer (but not usable) "throw".

And an "average moon lit night" ≠ "Full Moon".




My interpretation is that if the moonlight on an average night was adequate, what do I need a flashlight FOR?

I wonder at what lux the throw distance should be calculated so 99% of folks would not be disappointed or feel misled.
2 lux instead of 0.25 lux? 5? 10?
For me, I think 800 feet is the farthest I'll ever need to see. And I want at least 2 lux on target, so anything above 118k CD will be enough for me.
Going by 0.25 lux, the spec'ed throw would be 2,264 feet.

TEEJ said:

My interpretation is that if the moonlight on an average night was adequate, what do I need a flashlight FOR?

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Good point!

scs said:

I wonder at what lux the throw distance should be calculated so 99% of folks would not be disappointed or feel misled.
2 lux instead of 0.25 lux? 5? 10?
For me, I think 800 feet is the farthest I'll ever need to see. And I want at least 2 lux on target, so anything above 118k CD will be enough for me.
Going by 0.25 lux, the spec'ed throw would be 2,264 feet.

Click to expand...

Its somewhat distance and target contrast dependent.

For example, my guys can shoot a 3' paper target at 200 meters with 0.5 lux to 5 lux depending on their individual night vision, and, the quality of their scopes. If I use a rusty steel plate ~ 3' by 3' instead of a paper target, many can't even find it to aim at it without closer to 30 lux or more.

The rusty steel plate is low contrast, a white paper target is high contrast.

When closer, objects take up a larger proportion of your field of vision. As objects get progressively farther away, they take up a progressively smaller proportion of your field of vision.

As to see details, your central 2º cone of vision is required...objects that are smaller than your 2º field of vision are VERY hard to resolve at long distances. (Hence scopes and binoculars helping so much) Your vision within that 2º cone is your sharpest, best at tracking motion, and most sensitive to colors...but, the WORST in low light. So, if you are trying to see something small in your field of view, you need more light to do it than if it were proportionally larger...or closer, etc.

I have many examples of a light being able to shine on pages of a book as far as 500 meters away, so brightly that someone could read the book by that light.....and yet the guy SHINING that light can't see the book or the guy reading it by his light...because that amount of light is not enough to allow resolution at that range.

So the light was "reaching" the target...but, the 0.25 lux, that is absolutely adequate to follow a path to a latrine with, etc...is not adequate to see things far away.


So, 2 lux MIGHT be OK, for some things you are trying to see at night, or, it might be woefully inadequate...depending on how far away it is and how much contrast it has with its background.

20 lux might not be enough if you needed 30 lux, etc.

Thanks for the detailed explanation, TEEJ.
I guess bright is never bright enough and far is never far enough. That's why we're all still hanging around here, waiting for the next big thing.

scs said:

Thanks for the detailed explanation, TEEJ.
I guess bright is never bright enough and far is never far enough. That's why we're all still hanging around here, waiting the next big thing.

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LOL

Its just choosing the tool for the job.

Seriously, if a light says it has 3000 meters of throw, and people say "Why would anyone need THAT, you can't even SEE 3000 meters!" I try to point out that a light that can hit 0.25 lux at 3k meters can ALSO hit 25 lux at 300 meters...which might even be useful.