LEDs & Other Stuff - (Reference Guide)

You can use my calculation for any distance. You just not to calculate the lux value in that specific distance (or the Candela value, which is basically lux @ 1m). This always works!

Also see here. There is another formula for spot size using the focal length.

but my problem was another thing.not calculation of hotspot diameter.
main question is how can i have a small hotspot with my XHP70.2 and 76 milimeter spheric lens for atleast 1.5KM of throw.what is the solution?!

First you need to calculate if this is actually possible. What is the maximum possible luminance [cd/mm2] of the XHP-70.2? Can you achieve this in your light?

The thread I linked to shows you how to calculate throw based on luminance. You can calulate the maximum possible throw with the XHP-70.2 and your lens this way.



are these formules right and enough?
according to these formules luminance at 907m^2 with a 2 degree lens at 1KM distance is about 0.007cd/mm^2.are these calculation ok?

For reference, the GT70 has a FET driven 70.2 which is close to max output and the GT reflector is 118mm and it gets about 1600 meters. I think a shaved dome bumps it up to about 2000 meters.

My SP70 with 70.2 at about 12A and 71mm diameter reflector gets about 860 meters. Shaving the dome should bump up the throw to over 1000 meters, maybe 1100m.

The 70.2 is not known for its long throw. It’s a big led.

Here are luminance measurements for XHP70.2.

it says page not found!
but here i found luminance measurments.at 8.6 amperes it is 56.9 cd/mm2

Fixed the link, please click again.

i read this topic : Project Excalibur - Next Generation LED Thrower (many pics) - UPDATE 2018-01-24
that flashlight has a good throw and spot size near my goal.but i have a question.if in that project the led was XHP70.2 then what would happen?how was throw distance and spot size(at 1000meter)?

BTW:

you need an aspheric lens, not a spheric lens.

thank you The_Driver
i read your topic “Project Excalibur” and that was amazing.
but if you used XHP70.2 in that project then spot diameter was about 70 meter instead 10.6 at 1000m distance.am i right?

Thanks!

Probably more like 60m diameter for the XHP-70.2 with dome. If you want a smaller hotspot and more throw you should shave (dedome) the XHP-70.2.

Can you tell us the focal length of your lens (assuming that it is in fact an aspheric)?

my lens’s focal length is about 4.5cm .
at 7meter distance spot diameter is 70cm so by using triangle rules at 1000meter distance spot diameter is about 100 meter.

I calculate 124m diameter in 1000m distance using my method (ignoring the corners of the LED).

De-doming the LED and driving it with a high current (FET driver) will get you your 1.5km of throw. The hotspot will be 50% smaller.

i think 124 meter spot at 1KM isn’t that bad for XHP70.2 are you agree?
i’m using my DIY fet driver now and it’s max current can go around 20A.
i have another question.how de-doming can affect on spot diameter?

Here is a comparison I did using the xhp-70. The dome and die size is the same for 70.2, so I would expect the same difference in diameter. (The 70.2 has less donut hole shape)

(Size comparison only)

Read this.

i have an idea.can i use a 80 degree reflector in combination with my lens to collect whole light?is that a good idea?

No, that won't work (using parabolic reflectors). An elliptical reflector could work, but nobody really does that. A dual-lens system definitely works if you do it correctly.

Interesting how “dome off” makes the flag stand at attention.

:wink:

De-domed is a bit brighter & cooler with less spill and there’s a doughnut hole. I think I prefer domed, taking trade-off of brightness for warmer, smoother beam and greater spill.