Quantifying urban throw (the "washout effect")
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asdalton
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
[ QUOTE ]
Steve C said:
Forgive me if I wasn't clear, but in the scenarios (real deal in a cluttered back yard, etc.; not a parking lot) I was in, the LED light was simply swallowed up and never got to the shadow area; regardless of how close or far away I was. When I said the light was useless outside the pool of ambient light, I was serious.
[/ QUOTE ]
I would have to know what you mean by "the LED light"--and what you were comparing it to--before I could evaluate your experience in light of these charts, formulas, etc.
[ QUOTE ]
Steve C said:
Forgive me if I wasn't clear, but in the scenarios (real deal in a cluttered back yard, etc.; not a parking lot) I was in, the LED light was simply swallowed up and never got to the shadow area; regardless of how close or far away I was. When I said the light was useless outside the pool of ambient light, I was serious.
[/ QUOTE ]
I would have to know what you mean by "the LED light"--and what you were comparing it to--before I could evaluate your experience in light of these charts, formulas, etc.
asdalton
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
Ginseng,
Yes, my original wording about tight vs. diffuse beams was a little imprecise. I was implicitly thinking about two flashlights with comparable lumen outputs, such as the Scorpion and the L4. A wide-angle beam can put a lot of light on the target if the total output is huge. Supposedly this is what the Surefire M6 does, although I've never seen one in action.
Human vision is sensitive to ratios of intensities, and I believe that contrast is defined in that way (see the second link in my earlier post). However, our vision also gets pegged to an absolute level by the amount of ambient illumination. Compare the experience of looking outside from a darkened room at night, versus being outside on the lighted street and trying to look in. The person inside sees everything, while the person outside sees nothing.
Ginseng,
Yes, my original wording about tight vs. diffuse beams was a little imprecise. I was implicitly thinking about two flashlights with comparable lumen outputs, such as the Scorpion and the L4. A wide-angle beam can put a lot of light on the target if the total output is huge. Supposedly this is what the Surefire M6 does, although I've never seen one in action.
Human vision is sensitive to ratios of intensities, and I believe that contrast is defined in that way (see the second link in my earlier post). However, our vision also gets pegged to an absolute level by the amount of ambient illumination. Compare the experience of looking outside from a darkened room at night, versus being outside on the lighted street and trying to look in. The person inside sees everything, while the person outside sees nothing.
Re: Quantifying urban throw (the \"washout effect\")
Steve C.,
If the ambient is really bright and being reflected off objects into your eyes, it will take one heck of a lot of light to illuminate in its contrast. /ubbthreads/images/graemlins/icon3.gif There are conditions which can be so harsh that it would take lightning to overcome shaddows. Backlit conditions can be very demanding as well.
It would be very informative to know what LED light was totally useless in the situation you describe as well as to know what incan light was used or needed to overcome the ambient "set".
I personally think LED lights are great within their range and yes they have limitations. Since the 5W is the brightest in flux but a ***** to manage in small geometries for tight concentration of beam, let me set that one aside (but note how many who first hear about LED's and come to CPF almost immediately gravitate towards the 5W simply because of its high flux). Now give me a Lux III that is capable of say 50 lumens. Now you show me an incandescent that is also putting out 50 lumens and I think I can show you a LED light that will do rather well in terms of throw with the incan.
Steve C.,
If the ambient is really bright and being reflected off objects into your eyes, it will take one heck of a lot of light to illuminate in its contrast. /ubbthreads/images/graemlins/icon3.gif There are conditions which can be so harsh that it would take lightning to overcome shaddows. Backlit conditions can be very demanding as well.
It would be very informative to know what LED light was totally useless in the situation you describe as well as to know what incan light was used or needed to overcome the ambient "set".
I personally think LED lights are great within their range and yes they have limitations. Since the 5W is the brightest in flux but a ***** to manage in small geometries for tight concentration of beam, let me set that one aside (but note how many who first hear about LED's and come to CPF almost immediately gravitate towards the 5W simply because of its high flux). Now give me a Lux III that is capable of say 50 lumens. Now you show me an incandescent that is also putting out 50 lumens and I think I can show you a LED light that will do rather well in terms of throw with the incan.
leukos
Flashlight Enthusiast
Re: What exactly is \"throw,\" who knows?
[ QUOTE ]
Ginseng said:
Suffice it to say, the parameters of distance, focus and collection efficiency, source geometry and measurement device linearity interact to powerfully affect the applicability of the ISL as assumed for uniformly radiating point sources.
[/ QUOTE ]
Ginseng, you have my vote for CPF sentence of the week! Love the discussion! /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif
[ QUOTE ]
Ginseng said:
Suffice it to say, the parameters of distance, focus and collection efficiency, source geometry and measurement device linearity interact to powerfully affect the applicability of the ISL as assumed for uniformly radiating point sources.
[/ QUOTE ]
Ginseng, you have my vote for CPF sentence of the week! Love the discussion! /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif
Sway
Flashlight Enthusiast
Re: What exactly is \"throw,\" who knows?
[ QUOTE ]
Ginseng said:
Now that I've gotten all my term papers and finals out of the way, I promise I'll get back to my normal writing style. /ubbthreads/images/graemlins/wink.gif
Wilkey
[/ QUOTE ]
Thank you Incan Master maybe my head will stop hurting now /ubbthreads/images/graemlins/wink.gif
Eh' the only thing I have to add is if you can't see your target get a light brighter than the ambient lighting your trying to overcome that will throw through it, too much candle power is just about right /ubbthreads/images/graemlins/grin.gif
Later
Kelly
[ QUOTE ]
Ginseng said:
Now that I've gotten all my term papers and finals out of the way, I promise I'll get back to my normal writing style. /ubbthreads/images/graemlins/wink.gif
Wilkey
[/ QUOTE ]
Thank you Incan Master maybe my head will stop hurting now /ubbthreads/images/graemlins/wink.gif
Eh' the only thing I have to add is if you can't see your target get a light brighter than the ambient lighting your trying to overcome that will throw through it, too much candle power is just about right /ubbthreads/images/graemlins/grin.gif
Later
Kelly
TrueBlue
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
In the city a light is used differently than when it is used in no light situations.
When there is no light a flashlight beam is your eyes. 100% of the light beam is your only way to see in the dark. There is the light of your flashlight and inky black shadows. A single beam of light hampers your distance judgement. This is just like driving on a country road at night with one headlight broken. You cannot judge distance very well with only one beam because the brain processes light angles and two eyes to judge distance. Try throwing a ball at someone in the dark with only one flashlight. Most of the time you will not be able to judge the distance. In the dark you are truly impaired with Cyclops vision- a one angle beam of light.
Under ambient light situations a beam is used differently. Because of different light angles of ambient light and the flashlight you can now judge distance. The light now changes roles. You have the light around you but shadows are inky black. You eye's capability of seeing are on the threshold of identifying objects. You can just see enough to get around but not enough to identify details. Your color rendition is barely working. You can identify big objects but cannot identify any details in the darkly lit scene. And there is no light in the shadows to see anything. The lighting contrast ratio is too low.
A flashlight used in ambient light increases the visibility of an area that is illuminated by the flashlight and primarily to light up shadow areas. The beam increases the contrast ratio for your eyes to see by injection light in both light and dark shadow areas. The light will brighten both an area and the shadow equally to the point that you can see details.
Let's say for simplicity that the flashlight is twice as bright as the ambient light. The ambient light is one unit of light. Your light is twice as bright as the ambient light so it is equal to two units of light. One unit of ambient light plus one extra unit of light from a flashlight totals two units of light reflecting from a white object. In the shadows the light beam has also received light. There is no ambient light in the shadows but the flashlight is still lighting up the shadow area with one units of light. The unit of light on a white object in the shadow is also reflected back to you. Everything in the beam is brighter. The highlight area is brighter with two units of light and the shadow is now reflecting one unit of light. You can now see in the shadows as well as the ambient light area.
What the light beam has done is added an equal amount of light to both the bright and shadow areas. It becomes a 2:1 lighting ratio. Two units of light in the bright area and one unit of light in the shadow. Atmospheric obstructions can skew the color and distance the light travels. The lighting ratio would always remain the same but as the distance increases the light angle spreads out and dims the beam. . The lighting ratio would always remain the same but as the distance increases the light angle spreads out and dims the beam that hits the target and bounces back to your eyes.
In ambient light I don't really use a light to brighten the lit areas but more to brighten shadow areas. I have no problem with lighting in ambient light because my primary reason for using the light is not to light up brighter areas but to put light in the shadow areas.
Then again, I could be wrong. /ubbthreads/images/graemlins/smile.gif
In the city a light is used differently than when it is used in no light situations.
When there is no light a flashlight beam is your eyes. 100% of the light beam is your only way to see in the dark. There is the light of your flashlight and inky black shadows. A single beam of light hampers your distance judgement. This is just like driving on a country road at night with one headlight broken. You cannot judge distance very well with only one beam because the brain processes light angles and two eyes to judge distance. Try throwing a ball at someone in the dark with only one flashlight. Most of the time you will not be able to judge the distance. In the dark you are truly impaired with Cyclops vision- a one angle beam of light.
Under ambient light situations a beam is used differently. Because of different light angles of ambient light and the flashlight you can now judge distance. The light now changes roles. You have the light around you but shadows are inky black. You eye's capability of seeing are on the threshold of identifying objects. You can just see enough to get around but not enough to identify details. Your color rendition is barely working. You can identify big objects but cannot identify any details in the darkly lit scene. And there is no light in the shadows to see anything. The lighting contrast ratio is too low.
A flashlight used in ambient light increases the visibility of an area that is illuminated by the flashlight and primarily to light up shadow areas. The beam increases the contrast ratio for your eyes to see by injection light in both light and dark shadow areas. The light will brighten both an area and the shadow equally to the point that you can see details.
Let's say for simplicity that the flashlight is twice as bright as the ambient light. The ambient light is one unit of light. Your light is twice as bright as the ambient light so it is equal to two units of light. One unit of ambient light plus one extra unit of light from a flashlight totals two units of light reflecting from a white object. In the shadows the light beam has also received light. There is no ambient light in the shadows but the flashlight is still lighting up the shadow area with one units of light. The unit of light on a white object in the shadow is also reflected back to you. Everything in the beam is brighter. The highlight area is brighter with two units of light and the shadow is now reflecting one unit of light. You can now see in the shadows as well as the ambient light area.
What the light beam has done is added an equal amount of light to both the bright and shadow areas. It becomes a 2:1 lighting ratio. Two units of light in the bright area and one unit of light in the shadow. Atmospheric obstructions can skew the color and distance the light travels. The lighting ratio would always remain the same but as the distance increases the light angle spreads out and dims the beam. . The lighting ratio would always remain the same but as the distance increases the light angle spreads out and dims the beam that hits the target and bounces back to your eyes.
In ambient light I don't really use a light to brighten the lit areas but more to brighten shadow areas. I have no problem with lighting in ambient light because my primary reason for using the light is not to light up brighter areas but to put light in the shadow areas.
Then again, I could be wrong. /ubbthreads/images/graemlins/smile.gif
Re: What exactly is \"throw,\" who knows?
It was my understanding that the whole point about LED washout in urban setting was entirely due to the different light wavelength distribution between LEDs and Incandescents.
Regardless of if one color penetrates fog and mists better than another, what about the varying surface reflectivities and absorbtions of differing light wavelengths?
Throwing photons out there means nothing if all are absorbed and none are returned to the eye. It seems to me that a narrow wavelength light source and a matching absorbing material could make something very difficult to see as opposed to a broad spectrum source.
I think Don had us going in the right direction.
It was my understanding that the whole point about LED washout in urban setting was entirely due to the different light wavelength distribution between LEDs and Incandescents.
Regardless of if one color penetrates fog and mists better than another, what about the varying surface reflectivities and absorbtions of differing light wavelengths?
Throwing photons out there means nothing if all are absorbed and none are returned to the eye. It seems to me that a narrow wavelength light source and a matching absorbing material could make something very difficult to see as opposed to a broad spectrum source.
I think Don had us going in the right direction.
SilverFox
Flashaholic
Re: What exactly is \"throw,\" who knows?
This happens to be one of my favorite subjects... Although, I am still trying to understand it.
In reading through the references Andrew has indicated, I find it interesting that the section on visibility mentions that short wavelengths are absorbed more than long wavelengths. Perhaps this might give our study a direction to explore. If LED's are lacking in long wavelength light, they just might scatter more than incandescent light.
I believe we use the light falling on an object (lux) as a measure because normal lighting standards refer to it. When I measure a certain light value, I can assume that I will be able to see a certain amount of detail.
The problem may come from "the camouflage effect" of nighttime viewing. It is my humble opinion that a lot of natural scenes are lacking detail. In the daylight, there is sufficient light to observe very small differences in detail. At night, everything seems to "gray out."
If incandescent lights offer more contrast because of the light spectrum they operate in, they are perceived as being brighter and better. The higher spectrum of LED lights may reflect less contrast because the subject matter absorbs the higher frequency light. It also could be that the dust in the air has more effect on higher frequency colors.
If I am close on this, it could be that regardless of how many lumens we throw at this, the wavelength absorbing characteristic of the setting may be the controlling factor of how well we can differentiate detail.
I know that it is often necessary to doge and burn a landscape photograph in order to bring out the highlights that you hoped to capture on film. A straight print just seems to lack the snappy detail that made you shoot the picture in the first place.
On a side note, I was reading where Petzl has determined that the lower limit for useful illumination is 0.25 lux at 2 meters. This is supposed to be close to what moonlight is. I personally believe their idea of "useful light" is a bit optimistic, but if there is no ambient light, perhaps it is OK.
The inverse square law is interesting. I have an Aleph 3 that gives me different readings when I take them at 1 meter, or take them at 3 meters and calculate back to what they should be at 1 meter. I believe the readings at 3 meters are more accurate, but may have to get a better handle on the "extinction coefficient" before I know for sure. This behavior has also been noticed on many other more powerful lights.
If the inverse square law is true, I should be able to mount the light on a stand and measure out to where it drops to 1 lux. Comparing that distance with the calculated throw distances from measurements taken at 1 and 3 meters should help me determine which measurements are more accurate.
On the other hand, it may just open up a bunch of new questions…
Tom
This happens to be one of my favorite subjects... Although, I am still trying to understand it.
In reading through the references Andrew has indicated, I find it interesting that the section on visibility mentions that short wavelengths are absorbed more than long wavelengths. Perhaps this might give our study a direction to explore. If LED's are lacking in long wavelength light, they just might scatter more than incandescent light.
I believe we use the light falling on an object (lux) as a measure because normal lighting standards refer to it. When I measure a certain light value, I can assume that I will be able to see a certain amount of detail.
The problem may come from "the camouflage effect" of nighttime viewing. It is my humble opinion that a lot of natural scenes are lacking detail. In the daylight, there is sufficient light to observe very small differences in detail. At night, everything seems to "gray out."
If incandescent lights offer more contrast because of the light spectrum they operate in, they are perceived as being brighter and better. The higher spectrum of LED lights may reflect less contrast because the subject matter absorbs the higher frequency light. It also could be that the dust in the air has more effect on higher frequency colors.
If I am close on this, it could be that regardless of how many lumens we throw at this, the wavelength absorbing characteristic of the setting may be the controlling factor of how well we can differentiate detail.
I know that it is often necessary to doge and burn a landscape photograph in order to bring out the highlights that you hoped to capture on film. A straight print just seems to lack the snappy detail that made you shoot the picture in the first place.
On a side note, I was reading where Petzl has determined that the lower limit for useful illumination is 0.25 lux at 2 meters. This is supposed to be close to what moonlight is. I personally believe their idea of "useful light" is a bit optimistic, but if there is no ambient light, perhaps it is OK.
The inverse square law is interesting. I have an Aleph 3 that gives me different readings when I take them at 1 meter, or take them at 3 meters and calculate back to what they should be at 1 meter. I believe the readings at 3 meters are more accurate, but may have to get a better handle on the "extinction coefficient" before I know for sure. This behavior has also been noticed on many other more powerful lights.
If the inverse square law is true, I should be able to mount the light on a stand and measure out to where it drops to 1 lux. Comparing that distance with the calculated throw distances from measurements taken at 1 and 3 meters should help me determine which measurements are more accurate.
On the other hand, it may just open up a bunch of new questions…
Tom
Re: What exactly is \"throw,\" who knows?
This is interesting reading to be sure! /ubbthreads/images/graemlins/grin.gif I think Ginseng has hit on some key considerations in his discussion of perception because that's what it all boils down to and I think there is a strong case to be made that in some cases, we have more information than we suspect and in others we have actually less but "like" what we see. It is highly likely that a mono-chromatic light source selected for the best contrast in reflected as well as absorbed light in the target area of illumination would yield the greatest amount of information and yet we might prefer a broader spectrum providing color differences even at the expense of edge detection and acuity or sharpness in detail. /ubbthreads/images/graemlins/icon3.gif
For various reasons, it does seem that blue light is wayward and red likes to get absorbed leaving green and yellow to be sent out on recon and counted on for a return of information. /ubbthreads/images/graemlins/smile.gif Cyan is the best swimmer in the ocean and green does well in water with more sediment. We want them all to tell their stories but alas...........
For sake of delving further into the problem of the LED and ambient lighting, I still want specific examples of those that could and those that couldn't! As Andrew has stated, I still think the big difference will be found in flux and beam pattern and not so much of spectral origin. /ubbthreads/images/graemlins/icon3.gif
This is interesting reading to be sure! /ubbthreads/images/graemlins/grin.gif I think Ginseng has hit on some key considerations in his discussion of perception because that's what it all boils down to and I think there is a strong case to be made that in some cases, we have more information than we suspect and in others we have actually less but "like" what we see. It is highly likely that a mono-chromatic light source selected for the best contrast in reflected as well as absorbed light in the target area of illumination would yield the greatest amount of information and yet we might prefer a broader spectrum providing color differences even at the expense of edge detection and acuity or sharpness in detail. /ubbthreads/images/graemlins/icon3.gif
For various reasons, it does seem that blue light is wayward and red likes to get absorbed leaving green and yellow to be sent out on recon and counted on for a return of information. /ubbthreads/images/graemlins/smile.gif Cyan is the best swimmer in the ocean and green does well in water with more sediment. We want them all to tell their stories but alas...........
For sake of delving further into the problem of the LED and ambient lighting, I still want specific examples of those that could and those that couldn't! As Andrew has stated, I still think the big difference will be found in flux and beam pattern and not so much of spectral origin. /ubbthreads/images/graemlins/icon3.gif
NewBie
*Retired*
Re: What exactly is \"throw,\" who knows?
Contrast is important. In designing Avionics type displays, a person tries to increase the contrast. This can be done by putting out more light, or making the blacks blacker, or doing both. This gives you more contrast between white and black and makes the display much easier to read in direct sunlight. Also, a person can reduce reflections off a display surface, to reduce the reflected ambient light (or reflection of the sun), which mainly affects how black, blacks look in relation to the whites. You can also scatter the direct reflected light with a etched or rough surface. Index matching various parts within the display and also matching the display surface to the surrounding air, helps alot. Typically Magnesium Fluoride and Silicon Dioxide are used in multi-layer applications, and is commonly known as Anti-Reflection coatings, such are found on the nice flashlight lenses you buy from flashlightlens.com. This also increases transmitance, and can amount up to 8% gain in transmittance, and a easy 5x to 10x reduction in reflections.
One trick that was used with EL panels was to put a circular polarizer in front of the display. This prevents metallic parts from being seen from the outside, in bright light, since the polarization is opposite and doesn't make it's way back out.
Now, mentioning this, I've been surprised to not have seen any mention of circular polarizers or linear polarizers over a flashlight, and also the same in a set of vision glasses. This would help a fella to enhance or reduce glare off certain objects, and enhance the apparent contrast to the human eye.
You can go a bit further and start thinking about contrast between colors, and the peak wavelengths the human eye can see, or attack it by using shorter wavelength blue and longer red wavelengths. As soon as you start seeing light from true tri-band sources, say R, G, B bands, it's amazing how alot of things almost reach out and touch you.
You can get a little deeper, looking at the population of cones in the eye, and the distribution of R, G, B, as it changes, and is reflected in the CIE curves for a 2 degree and 10 degree observer. The target size actually makes a difference for seeing color.
There are lots of little neat tricks a fella can utilize to pull certain types of things out of a scene, that are within the grasp of the hobbyist....
Contrast is important. In designing Avionics type displays, a person tries to increase the contrast. This can be done by putting out more light, or making the blacks blacker, or doing both. This gives you more contrast between white and black and makes the display much easier to read in direct sunlight. Also, a person can reduce reflections off a display surface, to reduce the reflected ambient light (or reflection of the sun), which mainly affects how black, blacks look in relation to the whites. You can also scatter the direct reflected light with a etched or rough surface. Index matching various parts within the display and also matching the display surface to the surrounding air, helps alot. Typically Magnesium Fluoride and Silicon Dioxide are used in multi-layer applications, and is commonly known as Anti-Reflection coatings, such are found on the nice flashlight lenses you buy from flashlightlens.com. This also increases transmitance, and can amount up to 8% gain in transmittance, and a easy 5x to 10x reduction in reflections.
One trick that was used with EL panels was to put a circular polarizer in front of the display. This prevents metallic parts from being seen from the outside, in bright light, since the polarization is opposite and doesn't make it's way back out.
Now, mentioning this, I've been surprised to not have seen any mention of circular polarizers or linear polarizers over a flashlight, and also the same in a set of vision glasses. This would help a fella to enhance or reduce glare off certain objects, and enhance the apparent contrast to the human eye.
You can go a bit further and start thinking about contrast between colors, and the peak wavelengths the human eye can see, or attack it by using shorter wavelength blue and longer red wavelengths. As soon as you start seeing light from true tri-band sources, say R, G, B bands, it's amazing how alot of things almost reach out and touch you.
You can get a little deeper, looking at the population of cones in the eye, and the distribution of R, G, B, as it changes, and is reflected in the CIE curves for a 2 degree and 10 degree observer. The target size actually makes a difference for seeing color.
There are lots of little neat tricks a fella can utilize to pull certain types of things out of a scene, that are within the grasp of the hobbyist....
Icebreak
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
[ QUOTE ]
McGizmo said:
For sake of delving further into the problem of the LED and ambient lighting, I still want specific examples of those that could and those that couldn't! As Andrew has stated, I still think the big difference will be found in flux and beam pattern and not so much of spectral origin. /ubbthreads/images/graemlins/icon3.gif
[/ QUOTE ]
I mentioned earlier that the VIP with Otokoyama's BBH can. It can just about keep up with a WA1274 in a Mag. Totally blows a PM6 out of the water. It's odd to see that bluish round spot under a streetlight.
The beam has a visible hole in it to about 5.5'. It doesn't really get good convergence until about 7-8'.
However, in ambient light competing with a similarly throwing incandescent, I noticed this: Shine it at a black vehicle and it gets absorbed. The incandescent doesn't get absorbed nearly as much. So, I think wavelength is a player in the equation. How much of a player I'm not sure.
-------
- Jeff
[ QUOTE ]
McGizmo said:
For sake of delving further into the problem of the LED and ambient lighting, I still want specific examples of those that could and those that couldn't! As Andrew has stated, I still think the big difference will be found in flux and beam pattern and not so much of spectral origin. /ubbthreads/images/graemlins/icon3.gif
[/ QUOTE ]
I mentioned earlier that the VIP with Otokoyama's BBH can. It can just about keep up with a WA1274 in a Mag. Totally blows a PM6 out of the water. It's odd to see that bluish round spot under a streetlight.
The beam has a visible hole in it to about 5.5'. It doesn't really get good convergence until about 7-8'.
However, in ambient light competing with a similarly throwing incandescent, I noticed this: Shine it at a black vehicle and it gets absorbed. The incandescent doesn't get absorbed nearly as much. So, I think wavelength is a player in the equation. How much of a player I'm not sure.
-------
- Jeff
asdalton
Flashlight Enthusiast
Re: What exactly is \"throw,\" who knows?
SilverFox,
Keep in mind that "extinction coefficient" is relevant only to the loss due to absorption or scattering. The 1/r^2 law is a broadening effect and does not represent any loss of light from the total beam.
I was arguing that for a flashlight beam in clear air, the extinction coefficient is too small to have a detectable effect. The reciprocal of the extinction coefficient is the attenuation length, and it enters the loss factor as exp(-x/L), where x is the distance traveled by the beam and L is the attentuation length. If the attenuation length is 30 km--which is what that page gives for Rayleigh scattering of violet light--then over a path of 50 meters, about 99.8% of the emitted light will make it to the target. And that's in the worst-case wavelength.
Also remember that if short wavelengths were being preferentially scattered from a flashlight beam, then a bluish LED beam would cast a spot that appears not only weaker but also *yellower* with increasing distance. I have not seen any evidence of this happening.
The idea that a bluish flashlight beam scatters away in clear air reminds me of the urban legend regarding which direction toilets flush on the northern versus southern hemispheres. That is, it appeals to a sound physical principle, but when you look at the actual numbers it can't be significant.
SilverFox,
Keep in mind that "extinction coefficient" is relevant only to the loss due to absorption or scattering. The 1/r^2 law is a broadening effect and does not represent any loss of light from the total beam.
I was arguing that for a flashlight beam in clear air, the extinction coefficient is too small to have a detectable effect. The reciprocal of the extinction coefficient is the attenuation length, and it enters the loss factor as exp(-x/L), where x is the distance traveled by the beam and L is the attentuation length. If the attenuation length is 30 km--which is what that page gives for Rayleigh scattering of violet light--then over a path of 50 meters, about 99.8% of the emitted light will make it to the target. And that's in the worst-case wavelength.
Also remember that if short wavelengths were being preferentially scattered from a flashlight beam, then a bluish LED beam would cast a spot that appears not only weaker but also *yellower* with increasing distance. I have not seen any evidence of this happening.
The idea that a bluish flashlight beam scatters away in clear air reminds me of the urban legend regarding which direction toilets flush on the northern versus southern hemispheres. That is, it appeals to a sound physical principle, but when you look at the actual numbers it can't be significant.
Re: What exactly is \"throw,\" who knows?
What a fascinating read. This is good stuff indeed.
What a coincidence. Last night as I sat on the throne reading my B&H PhotoVideo catalog, I lingered on the section on camera lens filters (Hoyo, Tiffen, etc.) I even though about making some sort of thread mount (55mm for a Mag for example) for heads but the $40-90 price for a circular polarizer instantly put me off. It's a great idea though. I mean there are filters for color conversion (tungsten to daylight) and all sorts of other spectral management. Seems like a natural for flashlights.
I'm really enjoying the mix of reports of practical experience and theoretical noodling.
Wilkey
What a fascinating read. This is good stuff indeed.
What a coincidence. Last night as I sat on the throne reading my B&H PhotoVideo catalog, I lingered on the section on camera lens filters (Hoyo, Tiffen, etc.) I even though about making some sort of thread mount (55mm for a Mag for example) for heads but the $40-90 price for a circular polarizer instantly put me off. It's a great idea though. I mean there are filters for color conversion (tungsten to daylight) and all sorts of other spectral management. Seems like a natural for flashlights.
I'm really enjoying the mix of reports of practical experience and theoretical noodling.
Wilkey
asdalton
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
I did some quick & rough tests last night to see how well some different flashlights could illuminate the contents of a dark terrarium across two lighted rooms. The only incan that I had on hand was a Surefire E1e, but if we're looking for a mysterious "LED effect" then its modest brightness shouldn't matter.
Here are the comparisons, with Quickbeam's throw number in parentheses:
The Surefire E1e (25.22) beats
- Arc LSH-P (18.06)
- Nuwai 2xAAA (12.12)
- Surefire L4 (22.64)
- UK 4AA eLED (14.26)
It is beaten by
- Streamlight ProPolymer Luxeon (54.77)
- BugOutGearUSA LuxIII module (40.00)
- Surefire KL1 on 2 cells (40.00)
It's too bad that I don't have an MNO3 lamp, or else I would be able to construct an E2e to test out. But so far I'm not seeing any practical difference that the lux measurements aren't seeing.
I did some quick & rough tests last night to see how well some different flashlights could illuminate the contents of a dark terrarium across two lighted rooms. The only incan that I had on hand was a Surefire E1e, but if we're looking for a mysterious "LED effect" then its modest brightness shouldn't matter.
Here are the comparisons, with Quickbeam's throw number in parentheses:
The Surefire E1e (25.22) beats
- Arc LSH-P (18.06)
- Nuwai 2xAAA (12.12)
- Surefire L4 (22.64)
- UK 4AA eLED (14.26)
It is beaten by
- Streamlight ProPolymer Luxeon (54.77)
- BugOutGearUSA LuxIII module (40.00)
- Surefire KL1 on 2 cells (40.00)
It's too bad that I don't have an MNO3 lamp, or else I would be able to construct an E2e to test out. But so far I'm not seeing any practical difference that the lux measurements aren't seeing.
Re: Quantifying urban throw (the \"washout effect\")
[ QUOTE ]
asdalton said:
This may come as a surprise: "The nature of the multiple scattering also shows that no color penetrates fog better than any other." So much for those goofy yellow headlights. /ubbthreads/images/graemlins/smile.gif
[/ QUOTE ]
I do not think it is penetration but how our eye percieves light and what frequencies we are sensitive too. At the edge of our light sensitivity (with or without ambient light), I think THERE is where the light frequency comes into play. I would also refer to this read on Quickbeam's site LIGHT where, to sum it up, [ QUOTE ]
quoted from flashlight reviews.com: Our eyes are more sensitive to greenish-yellow than bluish-green. So it is better to be closer to greenish-yellow with our monochromatic color than it is to be closer to bluish-green.
[/ QUOTE ]
[ QUOTE ]
asdalton said:
This may come as a surprise: "The nature of the multiple scattering also shows that no color penetrates fog better than any other." So much for those goofy yellow headlights. /ubbthreads/images/graemlins/smile.gif
[/ QUOTE ]
I do not think it is penetration but how our eye percieves light and what frequencies we are sensitive too. At the edge of our light sensitivity (with or without ambient light), I think THERE is where the light frequency comes into play. I would also refer to this read on Quickbeam's site LIGHT where, to sum it up, [ QUOTE ]
quoted from flashlight reviews.com: Our eyes are more sensitive to greenish-yellow than bluish-green. So it is better to be closer to greenish-yellow with our monochromatic color than it is to be closer to bluish-green.
[/ QUOTE ]
asdalton
Flashlight Enthusiast
Re: Quantifying urban throw (the \"washout effect\")
The definition of illuminance (measured in lux) already accounts for differences in sensitivity to wavelength. So we do not have to apply any corrections if we are measuring lux directly.
We would need the corrections if we were measuring photon flux or energy flux. By those measures, the incandescent beam would look fantastic due to all of that infrared. But the infrared range is of course weighted to zero when the human eye is the standard.
The definition of illuminance (measured in lux) already accounts for differences in sensitivity to wavelength. So we do not have to apply any corrections if we are measuring lux directly.
We would need the corrections if we were measuring photon flux or energy flux. By those measures, the incandescent beam would look fantastic due to all of that infrared. But the infrared range is of course weighted to zero when the human eye is the standard.
Re: Quantifying urban throw (the \"washout effect\")
What I am thinking though that at the edge of human light sensitivity, Incadescents (with more yellow) will be more visible (of what light is reflected back) than LED lights (with more blue).
What I am thinking though that at the edge of human light sensitivity, Incadescents (with more yellow) will be more visible (of what light is reflected back) than LED lights (with more blue).
Re: Quantifying urban throw (the \"washout effect\")
These scenarios were detailed in some earlier (months back) threads, but they bear repeating here due to the inquiries. Let us hope that dano and a few other LEOs who have had similar experiences jump in with theirs.
Basically, I was in a rural, cluttered back yard that was illuminated by a rather weak sodium-vapor street light that the redneck had installed back there. I was using my brand-new L4 with one of Don's two-speed tail caps that I was SO proud of...
Anyway, we were searching back there looking for whatever. No immediate threat, but you never know... standing within the area lighted by the street light, the L4's beam would not light up the shadows. If you got right up to the edge of the ambient light spill, you could see a little ways into the shadows, but less than two or three meters.
The Stinger my partner was carrying lit those shadows up quite nicely; we could see easily into the tops of the trees and 25-30 meters into the underbrush. Needless to say, I went back to the unit and got my Stinger.
I was in a near-duplicate scenario behind a bar about a week later. This time I had my 6P, but I knew that one of the guys with us had a new L2. I borrowed it and went back there again; same deal, although the L2 did really light up the area- but it simply did not reach out past the ambient lighted area.
Again, I have no clue as to the cause of this phenomenon. I only know what I see. And again, while there may be some custom LED lights that will "punch through", that's not an option for me right now.
I have also conducted some "armchair enthusiast" experiments on my nightly walks. These are done in a well-lighted subdivision with sidewalks, etc. The A2's incan, and especially the 6P, will reach into shadow ares nicely. The L4 wouldn't, nor would a KL3 on a 6P body, nor would the X200 gun light I borrowed from a friend to check out; unless I was pretty close. From across the street? Forget it. I found that significant indeed.
So, while all these theories and discussions are interesting, I'll be keeping a strong incan as my primary light source when out and about at night... /ubbthreads/images/graemlins/grinser2.gif
These scenarios were detailed in some earlier (months back) threads, but they bear repeating here due to the inquiries. Let us hope that dano and a few other LEOs who have had similar experiences jump in with theirs.
Basically, I was in a rural, cluttered back yard that was illuminated by a rather weak sodium-vapor street light that the redneck had installed back there. I was using my brand-new L4 with one of Don's two-speed tail caps that I was SO proud of...
Anyway, we were searching back there looking for whatever. No immediate threat, but you never know... standing within the area lighted by the street light, the L4's beam would not light up the shadows. If you got right up to the edge of the ambient light spill, you could see a little ways into the shadows, but less than two or three meters.
The Stinger my partner was carrying lit those shadows up quite nicely; we could see easily into the tops of the trees and 25-30 meters into the underbrush. Needless to say, I went back to the unit and got my Stinger.
I was in a near-duplicate scenario behind a bar about a week later. This time I had my 6P, but I knew that one of the guys with us had a new L2. I borrowed it and went back there again; same deal, although the L2 did really light up the area- but it simply did not reach out past the ambient lighted area.
Again, I have no clue as to the cause of this phenomenon. I only know what I see. And again, while there may be some custom LED lights that will "punch through", that's not an option for me right now.
I have also conducted some "armchair enthusiast" experiments on my nightly walks. These are done in a well-lighted subdivision with sidewalks, etc. The A2's incan, and especially the 6P, will reach into shadow ares nicely. The L4 wouldn't, nor would a KL3 on a 6P body, nor would the X200 gun light I borrowed from a friend to check out; unless I was pretty close. From across the street? Forget it. I found that significant indeed.
So, while all these theories and discussions are interesting, I'll be keeping a strong incan as my primary light source when out and about at night... /ubbthreads/images/graemlins/grinser2.gif
