The There Are No Stupid Questions Thread

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JasonWW
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1stein wrote:
Mike C wrote:
I am by no means an expert but I’d say it’s all up to the reflector or optics. Too many variables to be able to use a simple formula.

I’m sure you’re right but since I’m interested only in hotspot I think the reflector has not that much impact?

Reflector makes a huge difference. It’s crucial.

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1stein
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JasonWW wrote:
1stein wrote:
Guys, I can’t find the answer although I’m pretty sure there is one within BLF “borders”. Hence my post here – I feel stupid asking you for a shortcut instead of making full research.

The question is: how to calculate the size of hotspot at a particular distance?

Let’s say I want a hotspot of diameter =3 meters at a distance of 150 meters. (numbers are taken out from nowhere, so might be odd). Which LED should I choose (de-doming/slicing is within scope of my poor abilities)?
Or the other way round. Let’s say I have Samsung LH351D, how can I know what would be the hotspot size at distance of 150 meters?

Your hints will make my research way easier.


There is only trial and error. Luckily there are already many different lights on the market so we kind of know how they scale up and down.

Basically it’s the ratio of die size to reflector size, assuming we are talking about basic flashlight design using a reflector. For a fixed reflector size, a smaller die creates a smaller hot spot and a bigger die makes it bigger.

For a fixed die size, a smaller reflector makes a bigger hot spot and a bigger reflector makes a smaller hot spot.

It’s easiest to just sample flashlights to see how they perform and decide if the hot spot is large enough and bright enough at the distance you want. If the hot spot is too small, you need to go with a bigger die or a larger reflector. If it’s too big, go with a smaller die or bigger reflector.

Typically a person will have a distance requirement, let’s say to easily see out to 200 meters. You can find lights that meet this requirement by looking for ANSI FL1 distance ratings of at least 600 meters. (Typically 1/3 the rating will be bright enough to see really well). Then it is a matter of how big of a hot spot do you want at that distance. A tiny 500 lumen black flat led in a Convoy L6 could easily do 600 meters, but it’s hot spot would be tiny. On the other extreme, a 6000 lumen xhp70.2 would also do 600 meters and make a huge hot spot. By keeping the L6 as an example host you have a full range of led die sizes to play with. Now you have to find the right compromise of flashlight size, weight, battery longevity, thermal control, etc… that best fits your needs.

Also keep in mind there will be a corona around the hotspot which will make the hot spot seem a bit larger. This means your “needed hot spot size at X meters” can actually be a bit smaller than you thought.

So based on what you need, folks here can get you in the ballpark, but it’s not an exact science. Reflector geometries and surface smoothness do tend to vary a little which throws off the calculations a bit.

Thanks Jason, after all I find your clues very useful. If I need to do it by iterations – fine.

Anyway, maybe somebody has already gone through the problem I’m analyzing now. To be more substantial: I need 3 meters hotsport at a distance of 70meters. I’m aiming to use Convoy L2, but then I’m confused if I should go for:
- Samsung LH351D (very welcome due to hight CRI) / “” De-domed?
- XHP50.2 De-Domed (since I’d rather throw over spill)
- Luxeon V
- SST-40 De-domed (less preffered due to greens and CRI)
- else?

Living in central Europe I don’t have that easy access to some less popular LEDs, so Arrows and other serious providers are out of my capability. Just common KD, BG, Ali, L4P, INTL… eventually MTN but very expensive and lenghty delivery.

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1stein wrote:

Anyway, maybe somebody has already gone through the problem I’m analyzing now. To be more substantial: I need 3 meters hotspot at a distance of 70 meters. I’m aiming to use Convoy L2, but then I’m confused if I should go for:
- Samsung LH351D (very welcome due to hight CRI) / “” De-domed?
- XHP50.2 De-Domed (since I’d rather throw over spill)
- Luxeon V
- SST-40 De-domed (less preffered due to greens and CRI)
- else?

Do you have the L2 or a light with similar sized reflector right now?

Keep in mind the Luxeon V, SST-40 and LH351D are all about the same die size, about 2mm x 2mm. No big difference there. Slicing the dome off will make the big difference. Xpl-hi is like a factory dedome and also 2mm x 2mm.

Then the 50.2 die is 3mm x 3mm. I would estimate the other 3 leds with dome on would make about the same hot spot size as the 50.2 with dome sliced off.

So all these leds and dome on or off will only give you roughly 3 different hot spot sizes.

Are you going to use the stock L2 driver or swap a new one?

User DTA has made many beam shot videos of lights at fixed distances. We can probably find the right led once we know the distances. I’m waiting on his response.

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Here is his video of the Convoy L2 with the xhp50.2.

I don’t know the distances in the video, but maybe it gives you a good visual idea of this reflector/led combo.

https://youtu.be/uS91E2×7hD4


.

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Jason, once again thank you for involvement. Yes, I have the L2 right now. I’m thinking of L4P 20mm driver since the flashlight is supposed to have just one mode (light for machine gun fixed on the car roof).
The bad news is L4P driver is not buck, so hard to use 2×26650 which I would wish to. Only 6V led would allow to do it without any further adjustments.

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Such deep thinking going on! Thought I’d “lighten” the subject a bit.

My idea of a good companion for my D4S—a Nite ) Ize Innovation holster

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JasonWW wrote:
Here is his video of the Convoy L2 with the xhp50.2.

I don’t know the distances in the video, but maybe it gives you a good visual idea of this reflector/led combo.

https://youtu.be/uS91E2×7hD4


.

Building on left is 125 meters and building on right is 30 meters.

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HKSJOSHUA_
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Hi did not think that holster would but had long lost that holster may pick one up

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Hi. A noob/stew-pid question.

What do the acronyms XHP-50.2, and SST-20 stand for? “Extra High Performance/Power?
Super Standard Transmittance?”

Also, what significance are the numerical designators. Especially the .2?

Thought I’d ask. Grad not

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https://www.cree.com/led-components/landing-pages/xhp “Cree Extreme-High-Power XHP LEDs”


As for the SST… I have no idea. Maybe contact them and ask  

EDC Rotation: ZL SC62 | Jaxman E2L XP-G2 5A | Purple S2+ XPL-HI U6-3A | D4 w/ Luxeon V | RRT-01 
EagTac D25C Ti | DQG Slim AA Ti | UF-T1 by CRX | Olight S1 | Klarus Mini One Ti
L6 XHP70.2 P2 4000K FET+7135 | Jaxman M8 | MF02 | Jaxman Z1 CULNM1.TG | Blue S2+ w/ ML Special
In-progress: Supfire M6 3xXHP50.2 
Others: Nitecore EC23 | Nebo Twyst | Streamlight ProTac 1AA | TerraLux LightStar 100

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SST – According to the datasheet it means “Surface Mount Package”. Though they used SFT for flat surface-mount LEDs too. By flat I mean that they didn’t have a dome.

.2 – this just denotes the second generation. In all Cree LEDs this means a completely different LED with much different properties. Sometimes better than the original, sometimes worse, often it depends on application.

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Fielding a few more questions, please.

What does a dome on the LED do, protect, and desensitize? Is that why domes are
Shaved, to allow full Lumens to shine thru? Innocent Allow more throw?

Is it a noobe possible task?

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Starkm32 wrote:
Fielding a few more questions, please.

What does a dome on the LED do, protect, and desensitize? Is that why domes are
Shaved, to allow full Lumens to shine thru? Innocent Allow more throw?

Is it a noobe possible task?


No, it improves light extraction.
That is: die emits some light, it enters silicone dome or a flat piece of silicone. Then travels across the silicone and hits silicone-air edge. At this edge some of the light passes but some reflects back.

With dome, light hits the silicone-air edge more perpendicularly. This reduces reflections and improves light yield.
Typically domed emitters give 10-20% higher light output.
But they also give less throw, much less.

See this to get a full explanation:
http://budgetlightforum.com/node/15818

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Starkm32 wrote:
Fielding a few more questions, please.

What does a dome on the LED do, protect, and desensitize? Is that why domes are
Shaved, to allow full Lumens to shine thru? Innocent Allow more throw?

Is it a noobe possible task?

The dome basically acts as a lens that enlarges the size of the LED’s phosphor relative to the reflector.

How easy removing the dome is depends on the particular LED. Some can be sliced easily, some should have the dome removed with a chemical solvent as physical cutting will damage it.

xevious
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Do many people here really examine those highly technical graphs (like CCT comparisons over runtime) that the most technical reviewers put in their content? I am impressed with the scientific and mathematical minds who endeavor to produce all of that work, but… I often wonder if it makes sense to only a very select few of BLF members. It often feels like such highly technical reviews require far more effort to produce than the very light given is even worth.

I do appreciate some graphs, like runtime on various cells, but in the end the aggregate performance numbers are my main interest (total runtime on each brightness level).

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Data are always good.

If people are willing to make those graphs, I’m always happy to have them. I’m an engineer and usually know how to interpret the graphs. If not, I can always ask Smile

Bear in mind that those graphs also supply the information that the “select few” can use to answer questions accurately and give good advice to the rest of us.

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xevious wrote:
Do many people here really examine those highly technical graphs (like CCT comparisons over runtime) that the most technical reviewers put in their content? I am impressed with the scientific and mathematical minds who endeavor to produce all of that work, but… I often wonder if it makes sense to only a very select few of BLF members. It often feels like such highly technical reviews require far more effort to produce than the very light given is even worth.

I do appreciate some graphs, like runtime on various cells, but in the end the aggregate performance numbers are my main interest (total runtime on each brightness level).

A lot of that info is relevant to choosing what emitters/drivers/optics/etc. work best in combination. For example seeing that the Nichia 219C has a low forward voltage means you do NOT want to put it in a single-emitter FET light. Some of the other info shows that new emitters render old ones obsolete (or that they don’t) based on things like color quality too.

Furthermore it shows how LED tech is advancing and just what kind of improvements/disadvantages things like the jump from the design of the XHP50/70 to the .2 versions offer.

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I have both the Astrolux ft03 versions. (sst40 & xhp50.2) I’m looking to dedome one of them. Which would be the best to dedome?

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Keep the sst 40 dome on the ft03 I cannot speak for the 50.2

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The XHP50.2 will be an easier dedome job since it’s a flip chip (no bond wires in top), on the SST-40 you’ll have to be cautions of the 2 bond wires plus the ESD protection diode.

Also, if the sst-40 in your FT03 is anything other than cool white it’ll be impossible to replace if you mess it up.

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Wouldn’t dedoming the sst-40 gain more throw than the xhp50.2?

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Well yes, but like I tried to explain its a notoriously hard LED to dedome and the supply of non CW SST-40s is literally non existent. If you mess it up on your first try you can not get another.

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The dome may also serve as a chemical seal to protect the phosphor from eventual contamination by volatiles coming from the soldering and heat transfer goop.

If you remove the domes you can buy a paint-on liquid sealer and apply that. I used to have a link for that stuff but can’t find it now.

There’s a lot written about failure modes for LEDs, problems that will start to appear over time (only after 10,000 hours, of course, trust the sellers on that).

https://www.tandfonline.com/doi/full/10.1080/09506608.2019.1565716

Quote:
Microelectronic components must be protected against the aggressive system and environmental stresses. This is routinely done by covering chips and other microelectronic components with a package that usually includes polymeric encapsulants to prevent the LED chip from being in direct contact with said environmental stresses. So, it is not surprising that many of LED failures are related to the package in a way or another. With that said, obviously, the right choice for packaging material is of crucial importance. The material used in LED applications should be stable enough to withstand the heat and high photon fluxes that occur in LEDs.

The main aim of this paper is reviewing the degradation and ageing mechanisms of different optical materials in SSL systems ….

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That makes perfect sense. What about a partial dedome? Not going too low as to harm the bond wires, yet still leaving a protective layer to protect the led?

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The word “dedome” implies removing the whole thing. With certain leds you can just slice off the top leaving a thin layer. This has almost the same effect. Candela increases a lot. Some leds are harder to slice than others and the results can vary. With the 50.2 folks recommend a “slice and dice”. You slice off the top and then slice off the sides. This is supposed to help remove some of the yellow corona and or spill, but when I tried the spill light stayed yellow.

It’s always best to have a spare led in case you don’t like the results or accidentally damage it.

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Thank you for the info!

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BurningPlayd0h wrote:
A lot of that info is relevant to choosing what emitters/drivers/optics/etc. work best in combination. For example seeing that the Nichia 219C has a low forward voltage means you do NOT want to put it in a single-emitter FET light. Some of the other info shows that new emitters render old ones obsolete (or that they don’t) based on things like color quality too.

Furthermore it shows how LED tech is advancing and just what kind of improvements/disadvantages things like the jump from the design of the XHP50/70 to the .2 versions offer.


That’s good to know. I guess that’s why the Nichia 219C has been popular for use in triple and quad emitter designs?
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Okay, here’s my No Stupid Question:

Is this a 7135 * 5 driver?

The missus must prepare the salaries of around 30 employees on a monthly basis (many still handed out as some staff don’t have / want bank accounts) and in addition sometimes have to check other papers of value for authenticity. That’s why she wanted a portable UV flashlight. Something better than the non-portable old and dim unit she now uses. The choice fell on a Convoy S2 Gray 7135 * 5 Driver 365nm Purple UV Flashlight. A seller was easily found on the internet, and the lamp was ordered.

Good price, a series of clear photos of the product and the following specifications were mentioned:

Features (shown in the main photo):

- Gray S2 LG UV 365nm
- LEUVA33W70RL00 LG UV 365nm LED
- 7135 * 5 1750 mA single mode
- ZWB2 filter, and a bit more down the page:
- High quality aluminum alloy.
- LG UV365nm LED 5W lamp beads are used.
- The built-in drive is 7135×5 single file.
- Life waterproof design.

Out of curiosity, and after playing a little while with the light (yes, we also got ourselves a pair or 3M safety glasses) I opened it and saw that the driver board looked different from the pictures of the seller. I know there is an (old/different?) version with the specs 7135 * 3 but I can’t find a good image of the 7135 * 3, or the 7135 * 5, let alone of the differences.

I know that the current stabilizers (I think that’s the right name but correct me if it isn’t) can/will be on both sides of the board, but because I didn’t take the light further apart I only see the two stanilisers on the spring side. As shown on the second photo both our 2 ‘black boxes’ are printed / engraved? with the text 7135 35P. I can find all different 35 codes, but not 35P. The seller’s photo (photo 1) does not show any visible markings (might be the lighting).

There is another small difference I noticed. On the light she has the name convoy is printed, whereas the seller’s photo shows the text convoy*2* (photo 3).

So my question is, can someone tell me if this is the 7135 * 5 1750 mAh version, or can it be that this is an older 7135 * 3 1050 mAh version? I’m just curious and if it’s not what she ordered I might leave a negative review on the seller’s webpage, to warn others. The missus doesn’t care too much, she’s running around and showing everyone the ‘miracles’ of this little flashlight (and looking silly with those glasses on but I don’t dare telling her afraid she will no longer wear them). I’m sure that by now it has some minor scratches or dents, so it stays, gets used, and abused.

Thank you all! Smile

The seller’s photo:

The light that came:

Inside the head:

JasonWW
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The 7135 is a current regulator. It allows 0.350 amps to flow (some do 0.380, but are not as common). Those drivers typically have room for 8 of these chips. It’s possible the other side has 4 chips making it a 6 chip driver, not 5. We don’t know for sure, though.

Another way to test is to measure the current draw through the battery. A 5×7135 driver should draw 1.75A. A 6×7135 driver should draw 2.1A.

Here are both sides of the same driver with 8 chips attached.


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Who doesn’t have direct deposit these days? My employer actually requires it. From my understanding, it’s expensive for an employer to actually cut a check.

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