sma tested it here (in German). A very high degree of precision is required to get the maximum benefit. So the people who only got 60% benefit simply need to position the collar more carefully.
The BLF GT reflectors measurements might be interesting for some people to play around with:
Diameter: 118mm
center hole diameter: 20.1mm
Max focal length: 11.5cm
Reflectivity: 90%
Cree XHP-35 HI diagonal: 2.9mm (2.5mm side length)
I will try to find it when I have time, it seems that I have deleted it from my desmos account so I canât get it immediately.
That will be really difficult, more of a job for an advanced ray tracing program
If you want to estimate stuff like that I suggest using this free software here: * OpticalRayTracer Home Page
Thanks, I will double check that everything is in mm and add labels for the units.
Do you know which one of the three imperial calculators youâre having the issues with?
Also, the way I calculated the max spot diameter is by taking the distance from the LED to the closest point on the reflector/lens (which is not equal to the focal point since there is a hole)
Then just using similar triangles, LED diameter / distance * 1km = spot diameter.
This is essentially the outer edge of the âcoronaâ.
Keep in mind I am using the MAX spot diameter, so that means using the diagonal LED diameter, not the side length.
You cannot use lumens=lux/m^2 because the brightness is not uniform, the outer edge of the spot will be much dimmer than the inner part of the spot.
Ok, that first part is very nice. I hadnât thought of that. So in my case it wouldnât be 20mm (only for an ideal point source), but 20mm - sqrt(2 * 1.06mm^2)/2 = 19.25mm
Why donât you implement both, outer edge corona and actual hotspot?
Ah, I found the bug, thanks. The new links I post should be fixed.
It will take a lot more calculations to find the true hotspot, because I need to figure out exactly where the projected images of the LED are overlapping the most, at the same time taht the images are changing in shape, and also moving away from the center of the spot.
Iâll have to spend some time thinking about that one and see if I can find an equation that isnât just brute-forcing the answer.
A parabolic reflector does not have a fixed focal length (is is not a lens). That is why I call it âmaximum focal lengthâ. The longest possible distance. Thus, there is also a minimum focal length. It depends on the type of light source used. With an LED it is the horizontal distance between the led and reflector surface (calculated above in post 13). With a bulb (emits light in all directions) it is half of this value, so 10mm.
One always needs to account for differences between the theory and the reflectors and light sources we use in practise.
It doesnât make sense to argue about the specific designations though. They donât change how we calculate things.
Iâm just going by what the datasheets of optics manufacturers say.
You can take the values from any one of their datasheets and plug them into the calculator and you will get a reflector that is exactly like the one they designed
I donât see your point? I never wanted you to use the âmaximum focal lengthâ for the calulation of the reflector.
It is only needed for calculating the size of the actual hotspot in a specific distance.
Or are you talking about the problems I had before? I was trying to test the imperial calculator by inputting the measurements (converted from metric) of the Maxabeam reflector. I got a different result. It didnât look right and the luminous flux values were off compared to the metric version.
I also checked and the metric vs imperial versions of the calculators should give the exact same lumen/lux values when you convert your measurements form mm to inches.
Ok, yes, I see it works. Sorry for being confusing. I never use the actual focal length for anything so I didnât think you might need it. I was inputting the wrong number. The metric and imperial reflector1 variants work nicely this way.
BTW: the imperial version still has some metric input boxes and calculates the reflector size in square millimeter. How about luminance in cd/inch^2?
I still think calculating the actual hotspot size (the smalles possible spot) makes sense. That is what we measure with lux meters. That is what people want to know.
Canât we just do it with the standard parabola equation? Please note that these are for an upright parabola centered on the y-axis. Yours is rotated 90 degress so you would need to switch the x and y designations.
We take half of the reflectors diameter, c/2, as the x-coordinate of the reflector point which is farthest away.
We then use the parabola equation y=((c/2)^2) / 4f to get the y-cordinate (f being the real focal length). So know we have the coordinates of a point on the rim of the reflector.
Now we just need the coordinates of the corner of the LED. That would be x=(sqrt(2*(s^2)))/2 and y=f.
So now we have two points and we can just calculate the distance between them.
dfmax = sqrt(((x2-x1)^2)+((y2-y1)^2))
dfmax is what I have been calling âmax focal lengthâ.
This allows us to calculate the actual âminimumâ hotspot diameter:
dhot = diameter_of_LED * distance_to_hotspot / dfmax
(This last calculation might require converting some of the units)
Yeah the imperial version still calculates mm^2 of the reflector because the standard way to measure intensity is cd/mm^2.
Since you donât have to care about the area of the reflector, itâs just an intermediate value in the calculation, I left it as mm^2.
The problem with the âinner hotspotâ is that for the type-2 reflector the shape of the reflected LED is getting smaller and smaller as you approach 90 degrees (the edge of the reflector) causing a âringâ of light that is not going to the center.
The farther off angle that the lens/reflector is from the LED, the more âskewedâ the image is.
If you look at an LED from 45 degrees, it looks like a trapezoid.
If you look at it from 180 degrees, it looks like a line.
Also, it doesnât matter if the parabola is vertical or horizontal, you can literally just switch the x and y in your equation to turn it sideways.
Well itâs not a âstandardâ calculator . Somebody who thinks in inches probably doesnât have a feel for square millimeters. Personally I think the imperial version is not needed at all, but then again Iâm not from the US.
You donât have to do it for both. You can just add it to reflector1 which is what 99.9% of lights have.
Yeah Iâll do that.
The reason I made a metric version was because I originally had only made an imperial version, because both optiforms and phoenix have all their reflector specs in inches.
For people who plan to order reflectors from them it is really easy to take the values straight from the data sheet and put them in without having to convert to mm
I guess I could have also built in a âmm or inchesâ option into the calculator to choose between the two. Maybe in a future update.