You are correct it’s not just the outer diameter that matters, it’s the frontal area. To find this you subtract the area of the small inner circle from the area of the large circle. But because of the way area grows with diameter the inner circle area is always relatively small. So making the reflector shallow, within reason, doesn’t have a huge effect on the frontal area.
This is not correct. Most flashlights use reflectors with similar collection angles. So would you expect, for example, that the BLF GT reflector would make a larger less intense spot than a C8 reflector, with the same LED? This is obviously not the case.
Please put your current understanding of this subject aside for a moment and read this:
Ok, I have been working on this and discovered an error on my part.
When I was making changes I was accidentally allowing the focus point to shift. But because it didn’t shift much, it went unnoticed. The error was even there in the reflector I printed.
So I came back to correct my mistake and hopefully explain this clearly.
,
For parabolic reflectors, you only have 1 thing you can change about the geometry. That’s the vertex location. (The vertex is a theoretical point behind the LED). The effect of moving the vertex away from the LED is more total offset of the reflector surface.
For thrower flashlights, you want enough offset to properly fit the reflector around the LED, and that’s it. Then the only choice that’s left is where to chop off the infinite geometry. You could call this the “diameter”, like The_Driver does… But this causes confusion, because as you see in the pic above, diameter isn’t forced to increase when you fiddle with the vertex. Diameter can be kept the same just by chopping off that infinite geometry sooner. Again, see pic.
You need to mathematically show how you derive the luminous intensity (= throw). That's what I did (even accounting for typical losses!). The size of the inner opening in a reflector has a very small impact on the overall frontal surface area (because the area of a circle increases with the radius squared). The radius (and thus outer diameter) is the deciding factor.
You have switched to using the term "performance" instead of "throw". How can you quantify that?
Do you own a lux meter? You could try doing some measurements with it.
I think the real issue here might be your understanding of what throw is?
We are talking about throw, so I don’t see an issue with the word performance, but I edited the word as you wish.
I didn’t say your math was bad. It looks good to me because you used “area” and subtracted the flat area around the emitter. It’s the fact you say front diameter is all you need to know that causes confusion. IRL it works well, but it causes confusion in discussions.
Saying throw is based on “area_circle - area_led_hole” sounds good to me. Saying it’s based on the front diameter only, confuses people. It confused me.
I really cant see how a lux reading at 1 meter gives any meaningful information on throw unless the divergence of the beam is taken into account also
for example i can setup a reflector that has a wonderful tight hot spot at 1 meter with very high lux reading but by 5 meters it will have flooded like crazy
Alternatively i could setup a well collimated beam with the same lux at 1 meter but it will still be concentrated at 5 meters
Obviously the later is going to go further
Maybe im just being thick here and missing something?
Well in this discussion we are only talking about parabolic throw reflectors, so in all cases the hotspot is mostly collimated. So they all act like lasers of varying area and lumens.
Though it’s also true that smaller reflectors suffer more from the LED not being an exact point source.
Ah ok so the lux at 1 meter to throw distance assumes a near collomated beam… that makes sense
it’s just i’ve never seen a torch beam that is even close to truly collomated or what id call properly collomated even the W30 diverges a fair bit but im used to working with lasers so perhaps i expect to much
I’d like to say thank you for the debate. Especially to The_Driver. If we hadn’t went on about this I wouldn’t have discovered the error in my 3D printed reflector geometry. And I also learned a better way to think about parabolic reflectors.
So I fixed the geometry error and supersized it!
It looks good with some sanding and painting. The took on an orange-peal look though. I will fix that some other day with a bit more sanding. I also had a problem with the 6” wide reflector bumping the limit switch on the printer. So the end of it is kind of messed up.
I had to make due with an E21A because that’s all I have on hand. I also chipped the phosphor last night.
We’ll see about a new reflector. I hate sanding.
Does anyone know how deep the BLF GT reflector is? I would guess around 80-90mm?? The front is 118mm. And I don’t think anyone has measured the flat area around the LED. One or the other is good enough to duplicate it.
Heck, is there specs online?
I spent 30 minutes jumping around that thread trying to find info. I’ve reached my limit, I need to do something more productive.
The only thing I saw was some calculations saying the base was 10mm, which is obviously wrong. It appears to be at least 3x-4x that in google images.
If anyone knows for finds out, I’ll print you a reflector for free.
