For sure in one of the flashlights the original emitter position was not optimal, because when I shimmed the reflector the hotspot and corona become bright and tight, then I tried to add another washer to see any difference and the beam was bad again with fuzzy hotspot.
On other flashlights maybe it's more a matter of preferences... instead of a big hotspot with thin corona, sometimes I get a smaller concentrated hotspot but with a bigger corona... Some compromise has to be accepted I think.
I respectfully disagree with this comment.
If you take a reflector of good proportions for throw (i would say ideal ) most, if not all the surface of the reflector would direct the light hitting it towards a ‘small’ hotspot.
If you then stretch this reflector to a bigger depth, then the curvature of the reflector would not be able to direct light to the center but rather close to it.
The actual reflector area that sends light to the center in smaller in the deep reflector.
The curvature of the parabola that redirects from point to point (like throw with led) is determined by a mathematical equation, is it not?
I'm a layman, so I can't get into the theory, but I can tell you an example of two reflectors where the shallow one gives a tighter hot spot, than the deeper one.
The first one is 29.5mm deep and the second one is 40mm deep. The shorter one is better at throwing a small center spot, with less side spill. The deeper one is better at flooding an area, with a much less defined hot spot and a lot of spill. Both tested with the same light (Maglite) and emitter (XM-L T6).
It's just an example that depth does not make the difference.
Ok, for fun and because my life is busy I took paper and scissors and did the quick experiment (how is the light coming from deeper part of the reflector different from the outer part). The flashlight is a budget 57mm xml-thrower on 5%low, 3 meter from wall:
Three times the same flashlight, without masking, with outside masked and with inside masked (first flashlight picture looks smaller, but was taken a bit further away, the beamshots were taken from exact the same distance, exposure was on automatic because what was relevant was spatial distribution, not brightness.
Bit roughly performed, but this shows nicely what you explained, drJ
I understand where you’re coming from with your argument, although your argument that increasing the depth of an ideal reflector reduces throw does not necessarily agree with the logic that let you conceive your ideal reflector [see (1) below]. But I believe you’re onto something.
However unreasonable it would be in real life, consider a reflector with a fixed diameter and infinitely adjustable depth. Assume it’s made from shape-shifting metal like the T1000 from Terminator 2 :cowboy_hat_face: .
Ignore the Inverse Square Law for a minute, and consider the ramifications of significantly increasing the reflector’s depth. This is not the same as changing the equation of the parabola; you are rendering the equation so the vertex [focal point] remains on the x-axis as you ‘stretch’ the ‘wide end’ of the reflector toward +∞ [see (2)]. The resulting beam from this reflector becomes closer to perfectly collimated as you approach the point when Depth/Diameter ≈ Depth/1. A white-wall shot would reveal the beam has uniform intensity, with no hotspot, corona, or spill.
(1) Our flashlights have reflectors small enough with emitters bright enough that we can essentially ignore the Inverse Square Law for our purposes [if reflectors have equal diameters, slightly different depths, and identical LEDs]. The ISL describes the relationship between light intensity and distance [Lux decreases exponentially with distance]. Thus, it’s imperative for any difference in distance that light has to travel [differences between reflectors of various depths and identical diameter] is kept “reasonably small” when drawing conclusions.
We can make these assumptions because the differences in depth between our various flashlight reflectors is tiny, or reasonably small compared to the distances our lights typically throw. There are other reasons, but that is probably the most pertinent and encompassing. These logical assumptions let you conclude that under most circumstances involving flashlights, a deeper reflector shouldn’t directly influence peak hotspot intensity compared to a shallower one. Unless the shallow reflector is too shallow too begin with…but that’s a special case.
(2) Analogous to plotting y(x)= x2 on a graphing calculator, and then zooming out so far that you can see x=∞ and y=∞ (obviously, not realistic but you can ascertain the significance in theory)
I’m just musing here, I’m no expert. So feel free to bash and put a dunce cap on me if I’m wrong :party:
The bottom line with throw is diameter and emitter (surface brightness).
If you want more corona, which won’t increase throw but may be useful (depending on your purposes) then go for a deeper reflector as well. This may be useful at intermediate distances.
If you want still more throw then replace the reflector with an aspheric lens. You’ll have no spill and a hotspot shaped like the emitter but it will throw further.
The greater the diameter the smaller and brighter the hotspot and therefore the greater the throw.
If you want a larger hotspot use a larger emitter (XL-M). If you want the greater surface brightness (throw) use XR-E or something similar.
That’s more or less all the factors other than driving the emitter as hard as is productive.
Keep in mind that the inverse squared law is the one that applies to throw so gains in lux have to be large to make much of a difference in reality.
Explanations given in these forums were thusfar always too unclear to me (and often not true), but, thanks to this thread, for the first time i get an actual grip on why xre-leds are, with their narrower radiation angle, so good in throw compared to newer leds
Uhm, actually XR-E’s narrower emission angle doesn’t help for throw, it’s just their higher luminance, or simpler put, their higher emitted lumens per square millimeter ratio.
Veeery interesting experiment, DJ I knew that for better throw you need a bigger reflector, but I didn’t know that the throwy part came from outer part of the reflector Spill depends on central part.
Could be very useful if you want to stipple your reflector. You can cover the outer part of the reflector with something and stipple only the inner part - you will maintain good throw but will get smoother spill
The curvature of the parabola can of course be defined mathematically, but a better way to visualize the geometry is via the conic section: http://math2.org/math/algebra/conics.htm
Since you can make a cone arbitrarily “fat” or extended, it’s easy to see there’s no restriction on dimensions.
Did you ever get a chance to look at why dedoming significantly increases throw? If anything it should be extracting more light from the high RI emitter. It makes no sense to me.
The shape is still parabolic. The key distinction to note here is that the telescope is built for rectilinear imaging (and thus relatively uniform magnification) whereas the parabola reflector is not. IThe hole experiment is supposed to show that the focal length (and by extension magnification) changes significantly towards the edge.
Surface brightness is the great claim to fame of the xre, but also; regarding that the outer part of a reflector contributes more to the center of the hotspot than the inner part, I suppose it helps that the xre-beam is narrower and thus makes less use of the inner part (bigger portion of the light in center of hotspot, less corona around it)
well, being a (convinced) biologist I settle for: experiments are fun
True, there are no restrictions on dimensions in general because all sorts of ratios provide different/diverse/interesting properties.
But to produce maximum throw, as this thread inquires, i find it a little hard to accept how there can be more then one ideal depth (given width).
Can more than on parabola shape (only depth to vary) be found that focuses a point to infinity?
A reflector for throw should only have spill and hotspot (as small as possible).
By making a reflector ‘shallow’, you let more light become spill, also light hitting the reflector will not bounce at the ideal angle to become ‘center hotspot’ producing large hotspot and flood.
By making a reflector ‘deep’, the light is again not bouncing at the ideal angle to become ‘center hotspot’ and produces larger hotspot and flood. What comes to compansate here is spill is less, spill moves to food and larger hotspot but not enough to compensate for the loss of ‘center hotspot’ thus throw.
That’s the conclusion I’ve come to. The JM05 clone I have is the same diameter compared with my Ultrafire C8, but much deeper.
It produces a much tighter hotspot, and also a much larger brighter corona, and although the hotspot is tighter it doesn’t seem as bright as the larger ultrafire C8, so I’m assuming Lumens are lost on the larger corona, and not really making any or little difference to throw.
Handy beam pattern though, it does give it more flood with the corona, without loosing any throw, albeit a tighter hotspot (with less lumens).
Thank for that info 
(it’s a pity you don’t have a lux meter :bigsmile: )
Physics is fun, isn’t it? 
Spill depends on central part.
