AilSnail
Flashlight Enthusiast
Could you clarify what you mean by focal spot? Do you mean the area of the die that is projected within a given angle, hitting a cd at 1m away for instance?
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Optic theory
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Could you clarify what you mean by focal spot? Do you mean the area of the die that is projected within a given angle, hitting a cd at 1m away for instance?
I think I am really dense here. :green:
From a distance, what object sees only a two dimensional surface? Is this object the source of light or an eyeball viewing the two dimensional surface being illuminated by the source of light?
From a distance, if I look into a flashlight, I agree I see a two dimensional disk of illumination. Obviously this disk will not appear to be the same brightness as my viewing location deviates from the Z axis of this disk.
I suspect I am not following your explaination well at all. I also can't buy into the statement:
THROW IS ABSOLUTELY NOT AFFECTED BY THE FOCAL LENGTH OF THE REFLECTOR OR LENS !!
In the case of a reflector held to a specific diameter (not a refractive lens):
By throw, I consider a measure taken at a consistant distance for both examples and from a position coinsident with the Z axis of the optic. Now this measure does involve collection of light over a finite surface and not at an infinitely small point. I assume that this measure will be maximum when a condition of focal length of parabolic reflector is best combined with the image (light source) and will be a function of the image size as well as its distribution pattern of light. As the focal length increases, the light managed by the reflector is better collimated but less overall lumens are managed by the reflector. As the focal is shortened (reflector getting deeper) more light is managed by the reflector but it is collimated to a lesser extent.
Let me try to explain with a specific example. Lets set a light meter at 10 meters from a Cree XR-E LED. THe light meter's sensor is centered on the Z axis of the Cree. We now place various focal length parabolic reflectors of 25 mm OD in front of the Cree LED and in such a focal adjustment that each registers maximum lux measurement on the light meter. I assume that if you were to graph lux measured against focal length that you would see some type of a bell curve where you would have a low lux reading for very short focal length reflectors as well as very long focal length reflectors and some optimal focal length identified by the top of the bell curve.
Am I false in this assumption?
AilSnail
Flashlight Enthusiast
This one again: Lux meters measures how many photons that fall upon them, just like my resistor does, right?
Aren't the photons coming from the arc light much denser (more photons per unit area) than those from the halogen?
Would this not mean that more photons are hitting the small measuring device (when it is smaller than the reflector) which is placed 1m away?
Look at the image in #36; If your eye is at the point where the yellow lines converge, you can't see the filament reflected near the rim of the deep reflector. Ergo the deep reflector is equivalent to a smaller reflector at this distance "downstream".
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Doug S
Flashlight Enthusiast
McGizmo said:
Let me answer a question entirely different from the one you asked (sound like anyone else we know :laughing: )
I am pretty sure your assumption is false if both your emitter and detector are infinitely small and the emitter is lambertian in its flux distribution. Note that is last qualifier belongs in much of the discussion in earlier posts.
Now in the case of your actual example where the apparent size of a Cree XR-E emitter is fairly large, it hurts my brain to try and reason it out. I'll leave that to others.
I think some of the general confusion you may be experiencing is that when Ra speaks of brightness he means photometric brightness (a.k.a., luminance) which in fact does not vary with the distance from source to viewer. It is measured in that wonderfully named SI unit, the nit.
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Doug S
Flashlight Enthusiast
AilSnail said:
Does this make them nitwits?
Sorry if this joke doesn't translate well for non-native English speakers.
Ra
Flashlight Enthusiast
McGizmo: You are getting there!!
The two-dimensional disk of illumination you see if you look into a flashlight from a distance is exactly what I mean (So, for a moment, you are the object that is lit by the flashlight!) !!
That disk always appears two dimensional.. So if you do the same with two flashlights: One with a deep reflector and one with a shallow reflector with the same diameter, YOU WON'T NOTICE THE DIFFERENCE !!
And now it comes: Only deviating from the Z-axis tells you which flashlight has a deep reflector: The disk of the shallow reflector will dim much sooner than the disk of the deeper reflector !!
At the Z-axis, the apparent brightness of the disk depends on only two things: The size, and the surface brightness: So a change in one of those two things (or both!) makes you receive less or more light (lux)
And Doug is right:
If you magnify a surface with a sertain surface brightness, the magnification of the brightness is exactly compensated by the.. (its always hard for me to find the right words in english..).. fact that you see a smaller part (or area) of the surface..
And AilSnail:
With focal-spot I mean the area at the focus of a lens or reflector that is nearly free of optical abberations. With a longer focal length that area is bigger than with a short focal length!
Thats why with a long focal length you are biggining to see the exact form of the emitter projected (square image of the Cree-junction on the wall..)
With a short focal length most of the led-junction around the focal-point is blurred by the abberations of the lens or reflector, so you'll only see a bright, fuzzy spot!!.
Next question please..
Regards,
Ra.
The two-dimensional disk of illumination you see if you look into a flashlight from a distance is exactly what I mean (So, for a moment, you are the object that is lit by the flashlight!) !!
That disk always appears two dimensional.. So if you do the same with two flashlights: One with a deep reflector and one with a shallow reflector with the same diameter, YOU WON'T NOTICE THE DIFFERENCE !!
And now it comes: Only deviating from the Z-axis tells you which flashlight has a deep reflector: The disk of the shallow reflector will dim much sooner than the disk of the deeper reflector !!
At the Z-axis, the apparent brightness of the disk depends on only two things: The size, and the surface brightness: So a change in one of those two things (or both!) makes you receive less or more light (lux)
And Doug is right:
If you magnify a surface with a sertain surface brightness, the magnification of the brightness is exactly compensated by the.. (its always hard for me to find the right words in english..).. fact that you see a smaller part (or area) of the surface..
And AilSnail:
With focal-spot I mean the area at the focus of a lens or reflector that is nearly free of optical abberations. With a longer focal length that area is bigger than with a short focal length!
Thats why with a long focal length you are biggining to see the exact form of the emitter projected (square image of the Cree-junction on the wall..)
With a short focal length most of the led-junction around the focal-point is blurred by the abberations of the lens or reflector, so you'll only see a bright, fuzzy spot!!.
Next question please..
Regards,
Ra.
Doug S,
I don't doubt my assumption is false if the emitter and measuring source are infinitely small but the reality is that they are anything but! :nana: Furthermore, when the term throw is used in regards to real flashights of real size illuminating items at a distance of real size and much larger in surface area than the surface aria of the two dimensional disk of illumination, I maintain that the deep reflector VS the shallow reflector does make a visible as well as measurable difference. Ailsnails images depict a projection of image that is not infinitely small in size. This is what we have to work with. A viable theory, in application or as a means to guide us, needs to account for this.
Hell, when one looks at the best reflector made or the cleanest and sharpest lens available and considers the surface at the scale of the photon that encounters it (forget infinitely small), these optics are anything but smooth and in compliance with the geometry they are to represent!
I realize this thread is about theory and it seems that Ailsnail is after a practical and realistic application of optic theory?!? I know I am but I am so limited in terms of realisim as well as practical that it's quite a challenge!
I think Ra has partially answered my question when he agrees that the disk of the shallow reflector will dim sooner but how is this effected by the relative size of the non infinitely small source of light compared to the focal length of the reflector?
My question about an optimal focal length based on optic diameter and image size has not been addressed to my knowledge beyond your pass on the question!
Instead of a light meter at 10 meters, I'll place a 36" diameter integrating sphere that has a 10" diameter open port alligned to the flashlight's Z axis. We will measure the lumens within the sphere. As I vary a 25 mm diameter reflector's focal length in front of the Cree LED, what happens to the reading of flux in the sphere? I consider a high reading within the sphere to equate with good throw.
I don't doubt my assumption is false if the emitter and measuring source are infinitely small but the reality is that they are anything but! :nana: Furthermore, when the term throw is used in regards to real flashights of real size illuminating items at a distance of real size and much larger in surface area than the surface aria of the two dimensional disk of illumination, I maintain that the deep reflector VS the shallow reflector does make a visible as well as measurable difference. Ailsnails images depict a projection of image that is not infinitely small in size. This is what we have to work with. A viable theory, in application or as a means to guide us, needs to account for this.
Hell, when one looks at the best reflector made or the cleanest and sharpest lens available and considers the surface at the scale of the photon that encounters it (forget infinitely small), these optics are anything but smooth and in compliance with the geometry they are to represent!
I realize this thread is about theory and it seems that Ailsnail is after a practical and realistic application of optic theory?!? I know I am but I am so limited in terms of realisim as well as practical that it's quite a challenge!
I think Ra has partially answered my question when he agrees that the disk of the shallow reflector will dim sooner but how is this effected by the relative size of the non infinitely small source of light compared to the focal length of the reflector?
My question about an optimal focal length based on optic diameter and image size has not been addressed to my knowledge beyond your pass on the question!
Instead of a light meter at 10 meters, I'll place a 36" diameter integrating sphere that has a 10" diameter open port alligned to the flashlight's Z axis. We will measure the lumens within the sphere. As I vary a 25 mm diameter reflector's focal length in front of the Cree LED, what happens to the reading of flux in the sphere? I consider a high reading within the sphere to equate with good throw.
Ra
Flashlight Enthusiast
Ok.. yet another computercrash after quoting...
To give an answer to post #43 (by AilSlail):
Seeing this from foton's point of view does even make this more complicated than it already is !!
And: You should never go too close to a torch with a aspherical lens or parabolic reflector: They are designed to send rays from a focal-point to a point at infinnity !! Comming closer than that will decrease their optimal performance!
With small reflectors in combination with Cree emitters, you can come as close as about 0.7 meter, if you come closer, the reflector-rim dims !
An extreme example: My super-creation Maxablaster:
And The reflector:
The reflector has a diameter of 230mm and the source is only 0.11 square mm !! 3300 lumens comming from a surface of 0.11 mm2 gives a huge, guge surface brightness: capable of illuminating things more than 4 miles away:
Ohhh Welll, Forgot my point: With this torch (big reflector, ultra small source) I need to walk about 200yards away to get the apparent reflector-disk fully lit over its entire surface by the source..
Regards,
Ra.
To give an answer to post #43 (by AilSlail):
Seeing this from foton's point of view does even make this more complicated than it already is !!
And: You should never go too close to a torch with a aspherical lens or parabolic reflector: They are designed to send rays from a focal-point to a point at infinnity !! Comming closer than that will decrease their optimal performance!
With small reflectors in combination with Cree emitters, you can come as close as about 0.7 meter, if you come closer, the reflector-rim dims !
An extreme example: My super-creation Maxablaster:
And The reflector:
The reflector has a diameter of 230mm and the source is only 0.11 square mm !! 3300 lumens comming from a surface of 0.11 mm2 gives a huge, guge surface brightness: capable of illuminating things more than 4 miles away:
Ohhh Welll, Forgot my point: With this torch (big reflector, ultra small source) I need to walk about 200yards away to get the apparent reflector-disk fully lit over its entire surface by the source..
Regards,
Ra.
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Ra
Flashlight Enthusiast
McGizmo, Please read post #5 and further.
There you can find the answers about grabbing more lumens from a Cree-emitter with a short focal length optic !!
You don't need a integrating sphere, we already concluded that you are collecting more lumens with a lens or reflector with shorter focal length..
BUT: THROW AND LUMENS-OUTPUT ARE TWO TOTALLY DIFFERENT THINGS !!
Take a 5mW laser-pointer: BAD LUMENS OUTPUT.. SUPER THROW !!
Put a CCFL-tube in a parabolic reflector: SUPER LUMENS OUTPUT... BAD THROW !!!
WHY?? Surface brightnessss : The laser-pointer beam comes from a 3mm lens and throws a mile !! A laser has the highest possible surface brightness..
The highest possible surface brightness with lamps: Mercury- short arc (Maxablaster)
Regards,
Ra.
There you can find the answers about grabbing more lumens from a Cree-emitter with a short focal length optic !!
You don't need a integrating sphere, we already concluded that you are collecting more lumens with a lens or reflector with shorter focal length..
BUT: THROW AND LUMENS-OUTPUT ARE TWO TOTALLY DIFFERENT THINGS !!
Take a 5mW laser-pointer: BAD LUMENS OUTPUT.. SUPER THROW !!
Put a CCFL-tube in a parabolic reflector: SUPER LUMENS OUTPUT... BAD THROW !!!
WHY?? Surface brightnessss : The laser-pointer beam comes from a 3mm lens and throws a mile !! A laser has the highest possible surface brightness..
The highest possible surface brightness with lamps: Mercury- short arc (Maxablaster)
Regards,
Ra.
AilSnail
Flashlight Enthusiast
double post
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AilSnail
Flashlight Enthusiast
I have done some more measurements, using up to three layers of the 50% film to make a somewhat fuzzy R/relative lux calibration curve for the photoresistor. There would be multiple error sources: transmission accuracy of the film, reflectivity of the film when in several layers, holding the lenses in front of the LED, battery level, heat, interpreting the splined graph with few data points, off hand. From that, it seems that the 38x55 is about 35% brightness of the 65x35.
I occluded the 38 and 65 to 14,5mm with a single piece of paper, the 27mm is too difficult to operate with this occlusion so I don't trust the readings I get with it.
65occ(14.5x45) - 0,95K
38occ(14.5x55) - 1.21K
This means that the shorter FL of same dia is 25% brighter (with an unknown error margin, probably huge) which may be accounted for by its grabbing more lumen due to the lower F/#?
I occluded the 38 and 65 to 14,5mm with a single piece of paper, the 27mm is too difficult to operate with this occlusion so I don't trust the readings I get with it.
65occ(14.5x45) - 0,95K
38occ(14.5x55) - 1.21K
This means that the shorter FL of same dia is 25% brighter (with an unknown error margin, probably huge) which may be accounted for by its grabbing more lumen due to the lower F/#?
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Doug S
Flashlight Enthusiast
Only the Dutch would illustrate their point with a windmill as a test target!Ra said:
Ra, the fact you felt the need to communicate this to me makes it clear that we are not communicating very well. My bad. Sorry for the interuption to this thread.
I would suggest though that lumens measured as collected by an integrating sphere at some distance from the source are somewhat akin to "throw" or at least my interpretation of the term. The integrating sphere can also measure lux based on port size and of interest would be the relative change in any of these measures as a result of alteration of focal length, ceteris paribus. In other words, in regards to throw, I am interested in the surface brightness of the target as it is illuminated by the distant source with optic applied. :shrug:
Doug S
Flashlight Enthusiast
If you define the problem as above, i.e., lumens falling within 10" (25.4cm for our SI friends) at a distance of 10m, then I believe that the problem is reasonably solvable with a flat emitting surface of defined area and lambertian distribution. I am also confident that others are better qualified than I to attempt it. See earlier comment about brain hurting. What throws a huge monkey wrench (or spanner for our Brit friends) into the analytical approach to this is that very non-lambertian distribution of the Cree XR-E. Pretend for a moment that the Cree's flux distribution is all within 35 degrees of central axis. In this case you can see that there is a large range of reflector focal lengths that will do absolutely nothing. You can also see that in this example that reflectors and lenses with the same diameter and focal length will give very different results. Perhaps for you, the very best approach is the empirical one which is also what you do the very best!McGizmo said:Doug S,
My question about an optimal focal length based on optic diameter and image size has not been addressed to my knowledge beyond your pass on the question!
Instead of a light meter at 10 meters, I'll place a 36" diameter integrating sphere that has a 10" diameter open port alligned to the flashlight's Z axis. We will measure the lumens within the sphere. As I vary a 25 mm diameter reflector's focal length in front of the Cree LED, what happens to the reading of flux in the sphere? I consider a high reading within the sphere to equate with good throw.
I just tried comparing 47mm with 60 mm FL AGAINST 52mmX37mm FL
lux reading (only for comparison purposes) @ ~3m
McR 27 reflector 50 lux
60mm FL ~1750 lux
37mm FL ~1930 lux
the 52mmX37mm has bigger hotspot and brighter too. So it is obvious which one will go to my light
lux reading (only for comparison purposes) @ ~3m
McR 27 reflector 50 lux
60mm FL ~1750 lux
37mm FL ~1930 lux
the 52mmX37mm has bigger hotspot and brighter too. So it is obvious which one will go to my light
AilSnail
Flashlight Enthusiast
Yep, some understanding (or creating a mental model) of how it works, and how to apply the understanding with calculations.
AilSnail
Flashlight Enthusiast
thanks for posting shiftD
Ra
Flashlight Enthusiast
Sorry McGizmo,
It is absolutely not my intention to offend you in any way. And you are very welcome in this discussion !!
Going this deep into things is dificult. As an optical engineer I have light and torchlights as a hobbie sinds I was eight years old... Did many tests to learn what is important with flashlights: How to increase throw for example..
And don't get me wrong: For throw, lumens indeed is an important factor: Without lumens, NO THROW !!
I thought I could convince you guyzz with the "what you see is what you get" approach: If a torch looks brighter from a sertain distance, that means that you are receiving more lux from that torch.
I also tried to explain that if you look at a diffuse surface with a magnifying-glass, surface brightness is not affected: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)
But the step from that to a lightsource seems to be dificult, but in a sence, its all the same: The piece of paper you are magnifying is a lightsource !
And AilSnail: If you want to measure the lux-output with your photo-resistor, it has to have a surface as small as possible !! You don't need filters if you are using the same lightsource. If you think you have too much light on the resistor, increase the distance, that is always better: if it is possible, at least 2 or 3 meter. Remember, in theory,, this theory only works at infinnity, so the more distance the better !!
EDIT: Ohh, I have a calibrated lux-meter, so I'm going to put my own theory to the test !!
Regards,
Ra.
It is absolutely not my intention to offend you in any way. And you are very welcome in this discussion !!
Going this deep into things is dificult. As an optical engineer I have light and torchlights as a hobbie sinds I was eight years old... Did many tests to learn what is important with flashlights: How to increase throw for example..
And don't get me wrong: For throw, lumens indeed is an important factor: Without lumens, NO THROW !!
I thought I could convince you guyzz with the "what you see is what you get" approach: If a torch looks brighter from a sertain distance, that means that you are receiving more lux from that torch.
I also tried to explain that if you look at a diffuse surface with a magnifying-glass, surface brightness is not affected: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)
But the step from that to a lightsource seems to be dificult, but in a sence, its all the same: The piece of paper you are magnifying is a lightsource !
And AilSnail: If you want to measure the lux-output with your photo-resistor, it has to have a surface as small as possible !! You don't need filters if you are using the same lightsource. If you think you have too much light on the resistor, increase the distance, that is always better: if it is possible, at least 2 or 3 meter. Remember, in theory,, this theory only works at infinnity, so the more distance the better !!
EDIT: Ohh, I have a calibrated lux-meter, so I'm going to put my own theory to the test !!
Regards,
Ra.
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AilSnail
Flashlight Enthusiast
Let us not give up on him yet!
pee break everyone!
AilSnail
Flashlight Enthusiast
true!
