Where does throw measurement stop?

[TwinBlade]

Is there a defining point to say "this flashlight has 122' of throw" or "my flashlight has 312 yards of throw"? At what point do lumens or lux cease to be a valid condition?

I mean, there are a LOT of folks in here that use 0.2 lumens at night for various tasks.

It just seems to be a gross generalization to me to say a flashlight will go out to a specified distance...according to what?

:shrug:

 

[RyanA]

I think lux is actually a better measurement than yardage. Yardage is subjective since there isn't also some specification as to how intense the light is at that range.

 

[red02]

Its up to the individual to determine how much lux they need on something to say that the light reaches that far. I think that 1lm/sq meter is not really helpful. My DBS is about 20k lux at 1m, which for my purposes is only good to 120-130m where its supposed to be good to 200m.

It seems that box measurements are rather arbitrary. I can't begin to guess how they arrive at the numbers they do.

Lux is the standard measurement for throw. However, while taking numbers like 20,000 lux and saying that the light will reach 200m is technically correct. It makes little difference since at that point its about a lumen spread across 1 sq meter. You also need to factor in beam divergence when talking about lux, as that, along with where you measure lux (ie 1m, 2m, so forth) will have a factor in how well the measurement can be used. Simply put, its complicated.

 

[TwinBlade]

I guess that is what I am asking. When they say "usable" light at 200 meters, or whatever the value, what do they consider usable? Some companies seem to under rate, some over rate. Just wondering if anyone knows of a standard or general rule that companies follow.:thumbsup:

 

[RyanA]

Yes, but a person is not a light meter. To a person one light might appear to throw father than another because it seems brighter at a given distance, when in reality the impression is false.

 

[RyanA]

I guess that is what I am asking. When they say "usable" light at 200 meters, or whatever the value, what do they consider usable? Some companies seem to under rate, some over rate. Just wondering if anyone knows of a standard or general rule that companies follow.:thumbsup:

Exactly, It's vague enough that it could really mean anything. Personally I'd prefer lux at a meter.

http://www.light-reviews.com/
This sight is neat in that they measure lux on each light they review. From that you can kind of guess at what a light with a similar optic, emitter and drive level would do.

 

[red02]

When dealing with lux, its helpful to remember the inverse square law. Such that lux/distance^2 will give you the lumens falling on 1 sq meter. Since we already know how much lumens translates into what relative brightness we can figure out if that light will give the needed amount of light at the desired distance.

 

[Flying Turtle]

Perhaps we need to develop something like an eye chart to gauge usable throw. Maybe a sign with one foot tall letters that read CPF.

Geoff