hi again
i bought a xhp70.2 for my diy flashlight
i have a question.i run the led at 1 watt and pcb temp was normal about 25 degree(room temp)but led surface(dome)temperature was about 45 degree.is that ok?
Absolutely perfect.
You will never have problems unless you go around 100 degrees Celsius.
thank you
i use a plano-convex for my flash light.lense’s diameter is 7.6 milimeter.
there is a problem with this lense.at 10 meter distance on a wall light’s diameter is about 70cm.but that is to much and i want it about 7-8 cm at this distance.which lense should i use for this goal?
I think there are 4 factors that affect spot size:
- Whether the lens if fully focused. Some lights purposefully don’t allow you to fully focus their lenses which makes the spot larger than it could be. Focusing better would make a tighter and more intense spot.
- F number. This is a parameter related to the exact shape of the lens. Lenses with smaller F number are stronger, if you used them for magnification - they would magnify more. F number affects distance from the LED at which the lens is in focus. A stronger lens will achieve focus closer to the LED. Now…please note that light that doesn’t hit the lens is wasted. Stronger lenses collect more light so they are more efficient. This efficiency makes the spot larger without making it less intense. Up to a point, very strong lenses tend to be less precise which hurts throw. You really need to test to tell whether you’ve got a good one. So…using a weaker lens would reduce your spot size. But it wouldn’t make it brighter. And I suppose that making it brighter is the whole point.
- Lens diameter. Larger lenses collimate better. This is directly proportional to lens frontal area. If you got a lens that has the exact shape of your current one but has diameter of 76 mm, the spot would be 10 times smaller in diameter (7 cm), 100 times smaller in area, 100 times more intense.
- LED used. LED die size is directly proportional to spot size. Using a smaller LED would make it produce a smaller spot. So changing from XP-L HI (3.55 mm²) to White Flat (1.069 mm²) would reduce spot area 3.32 times and spot diameter by 45%. If you use XP-L HI, going with 0.25 mm² Osram Synios would reduce your spot size to 19 cm. Spot area is proportional to die area. Spot intensity is proportional to die luminosity which is unrelated to die size - and changing LED may make your beam more intense but it can make it less intense as well.
thank you Agro
sorry my lens diameter is 76 milimetr and 7.6 is wrong!
about number 1:light is well focused.
number 3: lense diameter now is 76 milimeter an 760 milimeter is very huge!
number 4 :my led is XHP70.2 and i can’t change it.
but about number 2:you say if i need more throw then should use a lens with higher F number?my current lens has a F number about 4.5cm.so if i use a lens with F number of 8 spot size become smaller?but in this situation more light didn’t hit the lens!
Are you sure your lens is well focused at 4.5 cm? That would be extremely strong lens. I don’t think I’ve ever seen a plano-convex lens like that. If you try to move it a little farther from the LED, what happens? EDIT: I mixed up cm and mm
What else can you do to improve throw?
- try a higher quality lens
- better focus (IDK if the effet is large but some perfectionists say it is)
- you may gain some on AR coating as well (if your current lens is coated the gains are minimal)
- use a Wavien Collar
- these are hard to get
- dedome the LED
- drive the LED harder
Acting on point 2 won’t make the spot brighter unless the new lens happens to be more precise. Your current focal length is quite short but not extreme. You may gain some here but…just some, nowhere near your goal. And efficiency will suffer.
Diameter is not a factor for spot size when comparing fully focussed lenses. Only LED die size and the focal length of the lens determine it. Generally there are limits concerning the focal length though, meaning that it does increase with the diameter at some point.
As I said - with constant lens shape (and therefore constant F number), larger diameter makes the spot size smaller.
One can explain the same effects on thow and spot size by talking about shape and diameter like I did.
One can talk about focal length and diameter instead.
These approaches (as well as some others) are different but both are correct.
i will working on these ways after fully realizing F number and diameter effect on throw and select the correct lens.
this is what i realize :for smaller spot diameter i need a lens with higher F number and if i choose a lens with higher F number(more distance between lens and LED)then lens’s diameter unfortunately should be higher to prevent light losses; is that true?
One correction:
You use the “F number” where you really mean either “Back Focal Length” or “Focal Length / Effective Focal Length”.
See wiki to understand the difference between Back Focal Length (BFL) and Effective Focal Length (EFL or simply FL).
F number (F#) = EFL / diameter
F number is dimmensionless and depends on lens shape and material (but not size).
Focal length depends on both shape and size.
I explain that because the misunderstanding may lead to confusion at some point.
But you seem to understand this correctly now - a lens with longer focal length will produce a smaller spot, regardless of diameter. To concentrate more light on that spot (and therefore make it brighter) you can increase lens diameter.
thank you
but another question.
is that possible two lens with equal focal length and diameter but different build quality have different spot diameter?if yes which parameter affect this?
Precision can somewhat affect this. Though not much. Sometimes it may not be clear what to call “spot”.
Extreme case:
But beam artifacts aside - no, same focal length = same spot size.
it seems there is no way to have a small spot(my goal) with a 76 milimeter lens and collect whole light!
so is a reflector better than lens for this purpose?i think a reflector can collect more light(mean less losses) and can concentrate while light in one point and here there is no diameter’s problem of lenses.
is that true?
A reflector won’t help.
There are pretty much the same rules, throw is proportional to optics working area (note: reflectors lose a bit due to cutout in the middle which doesn’t contribute to throw).
A deep reflector can concentrate a lot of light which gives it a pretty large (and still intense) spot. But not more intense than that of a lens of equivalent size.
If possible for you, dedoming is probably the best thing you can do.
A Wavien Collar is probably the second.
for example BLF GT has about 2000meter throw.at 2000meter how much is spot diameter do you think?can i achive that with my lens and setup?
i have a XHP70.2 70CRI 6500K (6V)and a DIY driver that made by myself with 12A maximum current and a good 95watt cpu cooler.
There is. You need to use a pre-collimator (small spheric lens very close to the LED, LED needs to be de-domed). This is the only way to collect as much light as possible with an aspheric lens. If you then want a small hotspot, you just need to use a suitably small LED.
Here is a formula you can us to calculate the size of the hotspot:
luminous_intensity_in_specific_distance [lux @ xx m] = luminous_flux [lumens] / area [m2]
Generally you need to know how many lumens are actually in the beam. For reflector lights you can assume 75% of the total lumens.
Here you can find some nice calculators to help you.
this way is just for collect whole light.but thas is bad for spot diameter because it become bigger!
i was test it with a small lens(focal lenght=1cm and diameter=1.5cm) and not de-domed XHP70.2 and resault was a bigger spot and ofcourse more collected light.but i want a narrow beam with atleast 1.5KM of throw
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.