The surface area of a reflector (as seen from the hotspot, so a 2D circle) determines the throw for a given lightsource. It doesn’t matter how big or small the hotspot actually is. Only the luminous intensity matters (measured in candela or “lux@1m”).
The area of a reflector is mainly influenced by the diameter of the large opening because area_of_circle = radius^2 x pi. For a given outer diameter changing the depth of a reflector does have a small effect because the smaller hole at the bottom must get smaller. Thus the area is a bit larger, but it’s a very small effect.
Deeper reflectors do change the shape of the beam. The hotspot becomes smaller, the corona bigger, and the spill angle smaller compared to shallower reflectors of the same diameter.
The throw is determined by both the frontal surface area and the focal distance (the distance between the LED and the reflector surface)
I would say it is determined by the size of the parabola actually, the bigger the parabola (in relation to the LED) the better.
Depth doesn’t make too much of a difference, that’s why we see reflectors are usually shorter than their width.
Obviously the intensity will be higher with a tighter beam = smaller hotspot.
Have a look at how little more light is reflected when you make the reflector deeper:
(dark red is typical flashlight proportions)
You have to add a lot of depth to catch an additional 5° from the LED, it’s not worth it.
But, it wouldn’t add too much width in all, so you could go for square proportions (width = depth)
But let me say this:
I have a light with a very deep reflector, which i bought when i thought it would be good for throw.
Well, it isn’t good for throw.
The base of that reflector is considerably narrower than a short one of the same diameter, resulting in a weak beam with a corona as big as the spill.
I guess this could be useful in certain circumstances, but it mainly adds length to the head of the flashlight and not throw.
Nope, intensity is not higher with a tighter beam. A very common misconception.
Throw (cd) = luminance_of_lightsource (cd/mm^2) x surface_area_of_reflector_as_seen_from_hotspot (mm^2)
It’s that simple! You can actually calculate the luminous intensity and thus throw of a light before building it. It’s very accurate as long as your base values are accurate.
Of course this has nothing to do with how practical the beam of a light is or how big the spot is etc. Only the pure throw can be easily calculated.
So it’s not that shallower reflector throws better. For the given diameter, deeper throws better. For the given length, shallower throws better. For the given volume there’s some sweet spot which depends on the LED used.
No, just frontal area.
The distance between the LED and the surface of the reflector is what will dictate how “tight” the hotspot is.
For reflectors of the same diameter, a deeper reflector will have slightly higher lux due to the front area being larger (thanks to a smaller center circle)
It will also have a smaller “hotspot” thanks to the outer edges of the reflector being farther from the LED, and larger “corona” thanks to the inner edges of the refector being closer to the LED.
The overall intensity is a sum of all the projected die images, so the deeper the reflector is the more different the values between the inside and outside edges of the reflector become which causes the tiny center spot with large corona.
A very shallow reflector will have all the points on it’s surface about the same distance from the LED, which will give a clearer die image, closer to what you would see with a lens.
Yes with Wavien Collar. I considered using the Osram Synios but i have some kind of problem in my brain to power the LED in a Superthrower with just 1amp
There is less divergence with a ‘tighter beam’, there is less divergence with a larger parabola.
A (section of a) larger optic projects a smaller LED die. (This is also true for aspheric lenses).
That’s what i mean by ‘tight’. Collimation is better with a (section of a) larger optic.
This is why a deep reflector such as that 57mm one is disappointing, because the parabola is smaller than that of a regular one, despite the fact that it reflects more light coming from the LED.
Well yes, but the differences are tiny. Here is an example.
Lets say we have a Cree XHP-35 HI E2 @ 2.5A with a luminance of around 136cd/mm^2 (see luminance test here).
Lets say we want to put it into a Convoy C8, which has a medium-sized reflector (large opening has a diameter of 37.6mm). The light also has an ar-coated lens with 96% transmission (cheapo Chinese lens).
Imagine that we have two different parabolic reflectors (aluminium), both with the same large opening. One has a small opening with 5mm diameter and is deeper and the other has an opening with 10mm diameter (more shallow).
Area of first reflector as seen from hotspot: (37.6mm/2)^2 * pi - (5mm/2)^2 * pi = 1091mm^2
Area of second reflector as seen from hotspot: (37.6mm/2)^2 * pi - (10mm/2)^2 * pi = 1032mm^2
Luminous intensity with reflector 1: 136cd/mm^2 * 1091mm^2 * 0.9 * 0.96 = 128.2kcd
Luminous intensity with reflector 2: 136cd/mm^2 * 1032mm^2 * 0.9 * 0.96 = 121.3kcd
So with such a small reflector there is a measurable difference, but it’s still a small difference.
The thing to understand here is that the effect become less important the larger the reflector is.
Now the same calculation with the BLF GT reflector (118mm). Lets say we have one with a 20mm diameter small hole and one with 10mm.
Area of first reflector as seen from hotspot: (118mm/2)^2 * pi - (10mm/2)^2 * pi = 10,857mm^2
Area of second reflector as seen from hotspot: (118mm/2)^2 * pi - (20mm/2)^2 * pi = 10,622mm^2
Luminous intensity with reflector 1: 136cd/mm^2 * 10857mm^2 * 0.9 * 0.96 = 1,276kcd
Luminous intensity with reflector 2: 136cd/mm^2 * 10622mm^2 * 0.9 * 0.96 = 1,248kcd
So when using such a large reflector there is absolutely no discernable difference. Esepcially when you consider the minmum 10% tolerance of optical measurements.
The deeper reflector will make the light longer though. That is something you will notice.
Before you wonder why these values for the GT are higher compared to measurements which have been done, consider that this calculation assumes a perfectly shaped aluminium reflector with perfect 90% reflectivity with a perfectly positioned LED. It’s very difficult to reach the maximum possible value when building such a large light.
That’s what i said. This results in a far throwing light, it does not give it ‘more’ throw as in the amount reflected in the general direction forward.
Perhaps i’m not using the correct terms.
There will be more lumens wasted to make a wide corona compared to a shallower reflector, because the shallower reflector is wider at the bottom = longer focal distance = ‘tighter’ spot = better collimation = throwing farther.
The amount of light that is reflected on the outer edges of that 57mm deep reflector is only some 10° (see image).
It’s not worth it.
Look, i bought a TrustFire 168A in 2014, when i was new in this hobby.
I wasn’t able to make it throw, a C8 outthrows it, that is, it has a tighter and brighter hotspot.
No! You are argueing against simple physics. Sorry, but I have to write that.
The luminance of the LED and the front surface area of the reflector/optic are the only thing that matters for actual throw/distance. They determine how bright the hotspot is in the center. The reflector basically just multiplies the luminance of the LED.
Maybe another example:
Lets say you have two identical lights, for example two Convoy C8 lights. Both do 50kcd. When you hold them next to each eather so that the beams are parallel and overlap in the distance, you will get 100kcd. It simply adds up. This is the same thing I described above.
You not being able to make some cheap Chinese light with unknown properties throw further compared to some other light doesn’t really prove anything. We would need all the numbers, all the little details.
I’m not sure anymore.
One says this, the other says that, both make sense, but in reality my 168A sucks at throwing, but others seem to have had better results.
(from the reflector depth discussion in the GT thread)
Around 45° is ‘where it really counts’, and in this case the focal distance around that angle is 20% larger for the shorter reflector, which is around 20% shorter than the tall one.
Another example:
Take two LEDs and compare how much Candela they manage in the BLF GT.
A de-domed XP-E(1) @2A
2. A XP-L HI v3 @7A
The XP-L HI will throw further even though it’s 3.5 times as big (the die). Accordingly the spot will be 3.5 times as big when using the same reflector.
Why? Because it is so much more efficient that it manages a higher luminance at 7A.
Well, you forgot to mention the fact that this emitter will fade away in no time, speaking of personal experience ofc, especialy if that flashlight is moderately used
A dded XPL wont die that easy though
XPE2 at 2.5 amps will beat any XPL Hi /even dded XPL and will run and sing at 2.5 amps for a very long time
No, I don’t think so. The XP-L HI needs to be actually driven hard with a buck driver and multiple cells. Of course in single cell lights it’s not as good.
You are the only person I know of who reports problems with the reliability. There must be more…
