Bigwilly
Flashlight Enthusiast
- Joined
- Jun 14, 2014
- Messages
- 1,111
Candela.
Ok, I looked up lux and candela and they seem to be analogous? I guess I won't get it.
Lux measures lumens per square meter at a given distance. The ANSI FL 1 distance rating for a flashlight, for instance, gives the distance at which peak beam intensity is 0.25 lux.
Candela gives number of lumens per square meter, i.e., the lux, at a distance of 1 meter. Measurements of candela are usually made by measuring lux at distances greater than 1 meter, and normalizing back to 1 meter. This is so that a flashlight beam can focus properly before the measurement is taken.
Note: Checking with Wikipedia, I see that candela has a more complex definition than the one given above. For flashlight usage, however, I think the one above will suffice.
Uh oh. Now I want a "moonlight" level flashlight which has a distance sensor. I point the light at some object some distance away, adjust the brightness, and then the sensor maintains that lux as I move the light around, pointing it at things different distances away.
So I can point it at a tree over there, and then point it at my map, and then the ground in front of me -- and my eyes experience a constant level of brightness.
So if I'm standing in the dark, illuminated by some far off light source and 0.25 lux is shining upon me -- what do I see? How functionally bright is that?
If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?
It already was established that this is wrong. There is no given distance. It is just the light intensity at a given spot."Lux measures lumens per square meter at a given distance."
The easy answer is: Go outside on a clear night with half a moon. There is probably about 0.25 lux around you.So if I'm standing in the dark, illuminated by some far off light source and 0.25 lux is shining upon me -- what do I see? How functionally bright is that?
The binoculars don't change how much light (energy in form of photons) reaches you - it just makes it visually bigger. There might be a biological effect, that if you have a bigger light source you will excite more light receptors in your eye and therefore make it 'brighter'.If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?
If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?
I think the answer here depends on the binocular. Those with wide lenses gather more light than those with narrow lenses.
The binoculars don't change how much light (energy in form of photons) reaches you - it just makes it visually bigger. There might be a biological effect, that if you have a bigger light source you will excite more light receptors in your eye and therefore make it 'brighter'.
Objective diameter: The diameter of the objective lens determines how much light can be gathered to form an image. This number directly affects performance. When magnification and quality is equal, the larger the second binocular number, the brighter the image as well as the sharper the image. An 8×40, then, will produce a brighter and sharper image than an 8×25, even though both enlarge the image an identical eight times.
Source: Wikipedia
Lumens is more like "all the photons," while lux is the concentration of them at a single point.
If you shined a light into a lux meter and panned the light side to side, you'd see different lux readings in the hotspot, spill, etc.
To get lumens, you must perform math and have a device called an "integrating sphere." The sphere must be "calibrated," but this doesn't really involve changing the sphere but coming up with the calibration math. It's kind of a bumpy road to get started.
It already was established that this is wrong. There is no given distance. It is just the light intensity at a given spot.
Or, for a much rougher calculation of lumens, you could try the "integrating bathroom" instead of an integrating sphere.
Eyeball, smartphone app, manual camera, photog light meter, lux meter, etc (I've used them all), but as many have mentioned above, they all require calibration from a known/trusted output.
Surefire tried that with their Intellibeam, but CPF reports that it's flaky and kind of a lemon at this time. Maybe SF will clean up the problems, maybe the NLA it. Who knows?Uh oh. Now I want a "moonlight" level flashlight which has a distance sensor. I point the light at some object some distance away, adjust the brightness, and then the sensor maintains that lux as I move the light around, pointing it at things different distances away.
So I can point it at a tree over there, and then point it at my map, and then the ground in front of me -- and my eyes experience a constant level of brightness.
http://www.candlepowerforums.com/vb/printthread.php?t=200334&pp=30&page=1What's the cheapest somewhat accurate way to measure lumens? I have a lux meter app on my phone that I have calibrated to be somewhat accurate.
What's the cheapest somewhat accurate way to measure lumens? I have a lux meter app on my phone that I have calibrated to be somewhat accurate.
I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.
I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.
If you can, add ~$30 for a BLF favorite lux meter (LX1330B). With 1.5" PVC piping, my conversion factor comes out to a nice even 0.1x . It pegs my HDS 325 at both max and min, and also closely matches all tested modes (moonlight through max) for my 2 matching lights with ti-force (again, only reviewer on CPF to claim true ANSI and use laboratory tested calibration lights... he's about a third lower than SB in the <500 lm range I care about).
Note that it is best to calibrate from lower modes since max tends to be much more dependent upon sample, and of course battery age and state of charge. Well except for HDS, which are individually calibrated and with stone flat output/runtime curves.
I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.
If you can, add ~$30 for a BLF favorite lux meter (LX1330B). With 1.5" PVC piping, my conversion factor comes out to a nice even 0.1x . It pegs my HDS 325 at both max and min, and also closely matches all tested modes (moonlight through max) for my 2 matching lights with ti-force (again, only reviewer on CPF to claim true ANSI and use laboratory tested calibration lights... he's about a third lower than SB in the <500 lm range I care about).
Note that it is best to calibrate from lower modes since max tends to be much more dependent upon sample, and of course battery age and state of charge. Well except for HDS, which are individually calibrated and with stone flat output/runtime curves.