Group Buy Now Live - BLF GT90 SBT-90.2 powered 5,000 Lumen, 1.8Mcd / 2600m Super Thrower

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djozz
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For a hobby project with a SBT90.2 I bought this 13cm COB heatsink, it can passively dissipate up to 65W the description says.

I never change my opinion Big Smile , I still think that the GT should have been a box-design with a fat 15cm x 15cm flat heatsink directly behind the led Silly

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djozz wrote:
For a hobby project with a SBT90.2 I bought this 13cm COB heatsink, it can passively dissipate up to 65W the description says.

I never change my opinion Big Smile , I still think that the GT should have been a box-design with a fat 15cm x 15cm flat heatsink directly behind the led Silly

LOL, I actually still think that is a good option for the GT4 style light (assuming that it would be manufactured properly, which has been the issue so far, no one I trust to do it right), the GT didn’t output enough heat to make that necessary IMO.

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This is a review of the Astrolux MF05 Flashlight and it is compared to the GT90.
You cannot tell the difference in the video beam shots !!
The GT90 is on the left.
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https://www.youtube.com/watch?v=D5FGsnscboE
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CNC & Manual Machinist. Think outside the box too long , cannot find your way back in.

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Robin Dobbie
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djozz wrote:
For a hobby project with a SBT90.2 I bought this 13cm COB heatsink, it can passively dissipate up to 65W the description says.

How does one even measure temperature on an emitter like that? The large COB manufacturers have you glue a thermocouple to the aluminum base, but there’s no room on flashlight emitters.

Either way, when they provide a TDP of a heatsink, isn’t that based on an average sized item they’re assuming one might mount to it? The smaller the item, the lower the TDP. I think those are designed for large COBs. I would be interesting to see how close to 65w one could get with that and a 90.2.

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I never change my opinion Big Smile , I still think that the GT should have been a box-design with a fat 15cm x 15cm flat heatsink directly behind the led Silly

Why the tongue? Sounds like a great way to maximize the life and efficiency of the emitters without exposing the user and driver to hundreds of degrees.

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Robin Dobbie wrote:
djozz wrote:
For a hobby project with a SBT90.2 I bought this 13cm COB heatsink, it can passively dissipate up to 65W the description says.

How does one even measure temperature on an emitter like that? The large COB manufacturers have you glue a thermocouple to the aluminum base, but there’s no room on flashlight emitters.

Either way, when they provide a TDP of a heatsink, isn’t that based on an average sized item they’re assuming one might mount to it? The smaller the item, the lower the TDP. I think those are designed for large COBs. I would be interesting to see how close to 65w one could get with that and a 90.2.

Quote:
I never change my opinion Big Smile , I still think that the GT should have been a box-design with a fat 15cm x 15cm flat heatsink directly behind the led Silly

Why the tongue? Sounds like a great way to maximize the life and efficiency of the emitters without exposing the user and driver to hundreds of degrees.


You don’t really need to measure the LED temperature. The main reason for cooling is just so that you can hold the light without burning yourself. The actual LED can handle much more heat then your hand can. Over 200°C. The main point of cooling is just to prevent you from burning yourself.

You can get a rough idea of the wattage being put out by the LED just by calculating the voltage and amperage. I’m sure the SBT 90.2 is well over 100 Watts.

Heat sink with a large surface area like in the picture can work with a very small point source of heat if you use a good spreader such as an intermediary copperplate. Copper tends to spread the heat out very evenly.

Note, I’m not sure I interpreted what you asked correctly.

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I guess it depends on acceptable lifespans and output losses due to excessive temperature. But yeah, user comfort’s gotta be a big thing, too.

I’m just baffled by the unspoken rules that state all flashlights have to be round and have no active cooling. Or the ones that do have a fan, it seemingly has to be tiny, loud, and mostly ineffective.

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Robin Dobbie wrote:
I guess it depends on acceptable lifespans and output losses due to excessive temperature. But yeah, user comfort’s gotta be a big thing, too.

I’m just baffled by the unspoken rules that state all flashlights have to be round and have no active cooling. Or the ones that do have a fan, it seemingly has to be tiny, loud, and mostly ineffective.


The reason for thermal stepdowns and cooling is not about user comfort. It’s about not burning the user and getting sued.

There is nothing baffling about flashlights being round and no active cooling. The explanation is super simple. The round shape is dictated by the reflector. It doesn’t make much sense to machine a square flashlights and put a round reflector in it. Square is harder to machine and has extra weight compared to a round flashlight.

Adding active cooling tends to double or triple the cost of the flashlight and reduces the reliability. It also tends to compromise it’s water resistance. This is why you very rarely see it. Nobody wants to pay the price premium for it.

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Well, I think it’s necessary to measure the temps of your emitters, even if only in the design phase of a project. I think it’s important if emitter lifespan(which relates to reliability) and maximum output efficiency is a consideration. Which for me it would be, hence why I was asking how it was done.

djozz
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The tongue was because at the very start of the BLF GT project a few years ago, I was sideways involved and suggested a box design with handle (including a crude design drawing) with the led directly on the radiator, like the COB heatsink above. That design was never followed, BLF was in favor of the classic style flashlight shape, which happened. I’m still grumpy about that because I still think I was right. Flat Stare Big Smile

About measuring the temperature of your emitters: I’m all for measuring everything, but it is not needed everytime. After following temperatures and performance of a number of flashlight builds, over time you develop a feeling for how to mount your led, thickness of material for heatspreading, and size of radiators. I.e. that 13cm radiator combined with a SBT90.2 on a 30mm copper DTP board at 20A, will be fine (btw it will be bolted to a 20×20×0.3cm aluminium plate which adds a bit extra surface area for heat to radiate away). My educated guess is that after 8 minutes the radiator will be fully heated up and in steady state, about 90degC, by which time the 21700 battery already will be two-thirds depleted so that the current will drop significantly. Let’s see after the build if I guessed that right Smile

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djozz wrote:
The tongue was because at the very start of the BLF GT project a few years ago, I was sideways involved and suggested a box design with handle (including a crude design drawing) with the led directly on the radiator, like the COB heatsink above. That design was never followed, BLF was in favor of the classic style flashlight shape, which happened. I’m still grumpy about that because I still think I was right. Flat Stare Big Smile

About measuring the temperature of your emitters: I’m all for measuring everything, but it is not needed everytime. After following temperatures and performance of a number of flashlight builds, over time you develop a feeling for how to mount your led, thickness of material for heatspreading, and size of radiators. I.e. that 13cm radiator combined with a SBT90.2 on a 30mm copper DTP board at 20A, will be fine (btw it will be bolted to a 20×20×0.3cm aluminium plate which adds a bit extra surface area for heat to radiate away). My educated guess is that after 8 minutes the radiator will be fully heated up and in steady state, about 90degC, by which time the 21700 battery already will be two-thirds depleted so that the current will drop significantly. Let’s see after the build if I guessed that right Smile

LOL, I still think the box idea is a really good one, just for a different style of light. I have a few ideas bouncing around that would make really good use of it but sadly have not found a manufacture I trust to do it properly and done wrong it would ruin the whole concept in the eyes of manufactures.

Also agreed that it is not necessary to take detailed temperature readings for flashlights most of the time. First off with modern copper MCPCB’s the temperature of the shelf is pretty close to the temperature of the LED itself. Meaning you can get a really good idea of the temp with an IR thermometer on the outside of a light and modern LED’s are generally rated for up to 150c+, so it is highly unlikely you will be anywhere near that regardless.

Basically I have never had an LED die due to age, this is not a real concern for flashlights that would be lucky to get a few hundred hours of use with LED’s that are rated for 50k hours.

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I wonder if monitoring output drop is a valid way to test temperatures? If a datasheet has the lumen output at both 25C and 85C, and the difference in output is almost always 10%, can you just look out for a 10% luminosity drop from turn-on and know that’s 85C-ish?

I want to make a light where there’s only these considerations:

Comfortable and safe(light weight, no uncovered parts that can burn anyone)
stable and continuous maximum output for hours and hours(external power)
high maximum output(25,000lm)
low price(relatively)

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Robin Dobbie wrote:
I wonder if monitoring output drop is a valid way to test temperatures? If a datasheet has the lumen output at both 25C and 85C, and the difference in output is almost always 10%, can you just look out for a 10% luminosity drop from turn-on and know that’s 85C-ish?

No, there are too many other factors to give an accurate correlation.

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Even if you account for power? Like if the voltage and current are precisely the same at the test intervals?

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Robin Dobbie wrote:
Even if you account for power? Like if the voltage and current are precisely the same at the test intervals?

Correct. The heat slowly flows from the head of the flashlight all the way to the tail. The entire flashlight will start to get warmer and warmer. Then you have the ambient air temperature around the flashlight as well as how much air is circulating around it. There’s both convection and radiation removing heat. If you happen to hold it in your hand then you also have conduction taking place removing heat through your hand.

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Robin Dobbie wrote:

I want to make a light where there’s only these considerations:

Comfortable and safe(light weight, no uncovered parts that can burn anyone)
stable and continuous maximum output for hours and hours(external power)
high maximum output(25,000lm)
low price(relatively)


Anything over 6,000 or so lumen is going to require active cooling, so there goes any chance of a low price.

Lower powered lights like the PowerTac X10000 Destroyer or X10k cost $700 and thats only 10,000 lumen.

The Microfire Challenger H5 was 5,000 lumen and cost about $475.

I think the light closest to 25,000 lumen and lowest in cost is the imalent R90C at about $400.

I did a thread on a lot of active cooled lights here if your interested. It’s not up to date, though. Imalents newer lights are not on there.

Very few lights use external power. I remember the old Olight X6 Marauder, but it was only 5,000 lumen and $400.

Any light capable of 25,000 lumen for just 1 hour is going to require a massive amount of battery capacity. It would almost have to be externally mounted. The only real application I could think of for the light you’re describing would be some type of search and rescue. This is a specialty application so it would be well beyond and above any type of reasonable cost. Not at all something the average flashlight user would need or could afford. It sounds like something a city’s Fire Department might use and a city can afford to pay the big bucks for a specialty light.

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Let me rephrase.

If we have a completely stable cooling and power solution which continuously keeps the light within 10% of measured turn-on luminosity, could we be reasonably certain that the junction temperature of the emitter(s) is not significantly exceeding 140-150C?

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Robin Dobbie wrote:

Comfortable and safe(light weight, no uncovered parts that can burn anyone)
stable and continuous maximum output for hours and hours(external power)
high maximum output(25,000lm)
low price(relatively)

To reach 25k lumens, you are going to need to dissipate around ~250w as a rule of thumb (yes you can get better efficiency then this but it requires more LED’s and thus a larger light and less throw as a rule).

People greatly underestimate the amount of cooling needed for long term use. Check out the massive heat sinks that CPU’s use WITH fans and consider that most of those are only rated for ~150-200w. So you would need one of those big CPU coolers with a fan or 3 to have a chance of cooling such a light. This rules out light weight and small size.

Then you have the costs to build all of this, as Djozz said, 2-3x the price is a good guess all said an done.

And after all of that, the power required to actually power this light would drain a 18650 cell in about 2.5 mins, or it would require a 20A+ connection to a car battery (cigarette lighter is only rated for 10A) OR it would require a power brick the size of a xbox 360.

There are always going to be trades off’s like anything in life. If you want high output and long runtime, you throw size, complexity, power constraints and usability out the window (think work light or off-road truck light-bar).

The GT4/GT94 is pretty much the best you can do in it’s form factor for a passively cooled light. Anything more then this would need active cooling and a much higher price tag.

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Robin Dobbie wrote:
Let me rephrase.

If we have a completely stable cooling and power solution which continuously keeps the light within 10% of measured turn-on luminosity, could we be reasonably certain that the junction temperature of the emitter(s) is not significantly exceeding 140-150C?


I don’t know. At this point your basically doing a laboratory based test. You can probably attach a probe or IR meter as close as possible to the junction and assume it’s slightly less hot than the junction itself. I still would not trust there is direct correlation between the output in lumens to the junction temperature. Maybe there is, but you’d need to test it to confirm.

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Absolute throw isn’t necessarily what I’m after. The hours and hours of power would come from the wall. Although with, say…(16) 35Es, one could achieve well over 20,000lm for an hour.

There are heatsinks which dissipate close to 400 watts for less than $50. Fans that are waterproof, rated for 150K hours, and relatively quiet for less than $30. Every year at Computex, Noctua has their $90 heatsink set up dissipating a 440W synthetic load. It’s keeping something the size of a CPU at 440W less than 85C, continuously! That 15CM box djozz is talking about is starting to make some sense. They’re also demoing a fanless 120W sink they say they’re trying to keep under $100. It’ll be interesting to see what comes from it.

Anyway, powerful video and photography lights are already a thing. They’re just astronomically priced compared to the off-the-shelf parts they could be made from. Figured there could be an opportunity for a BLF project.

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With qty 10 of XHP70.2's putting out a total of 25000 lumens, it would use about 150 watts.

Of course running under wall power, we are not talking about a flashlight, but rather auxiliary lighting. It's really outside the realm of what we do here.

I dunno what those heatsinks look like, specially interested in the ones you mentioned for less than $50 -- do you have a link or 2?

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Robin Dobbie wrote:
Absolute throw isn’t necessarily what I’m after. The hours and hours of power would come from the wall. Although with, say…(16) 35Es, one could achieve well over 20,000lm for an hour.

There are heatsinks which dissipate close to 400 watts for less than $50. Fans that are waterproof, rated for 150K hours, and relatively quiet for less than $30. Every year at Computex, Noctua has their $90 heatsink set up dissipating a 440W synthetic load. It’s keeping something the size of a CPU at 440W less than 85C, continuously! That 15CM box djozz is talking about is starting to make some sense. They’re also demoing a fanless 120W sink they say they’re trying to keep under $100. It’ll be interesting to see what comes from it.

Anyway, powerful video and photography lights are already a thing. They’re just astronomically priced compared to the off-the-shelf parts they could be made from. Figured there could be an opportunity for a BLF project.

Yep, I have considered many of these things as well. As djozz pointed out earlier, besides the technical limitations, the biggest hurdle is cost.

To make a light with a Noctua style heatsink you would easily be pushing the price over $1000, most likely WELL WELL over that since it would be a very small quantity light and thus very few lights to spread the R&D costs over.

That said, Djozz box light idea is the best compromise I have heard so far but still presents a lot of design and manufacturing challenges. I have put feelers out for such a light a few times but everytime decided to not pursue it as the manufactures were just not ready for such a light.

It will be a big departure from what they know and having been behind the curtain so to speak, I just simply have not found a manufacture that I think could pull it off properly yet. That is even before trying to convince them to give it a try knowing there will not be much profit in it (which means it would get even less attention in the design phase when it needs far more).

There are a few lights people have put together on youtube using CPU water coolers for big output, they are really neat but very hard to turn into a practical flashlight.

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My challenge is good drivers. But what’s cheap technically works with workarounds.

But yeah, I guess manufacturers agree with you on the price. Was just looking at a 30,000 lumen studio light that costs $2000 retail. 10,000 lumens for $1000.

But the difference between a studio light/aux light and flashlight at these output levels is just conceptual. If we can pack twice the batteries onto a “studio” light and still have it weigh less and operate 4x as long as a “flashlight” then …

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Tom E wrote:

With qty 10 of XHP70.2’s putting out a total of 25000 lumens, it would use about 150 watts.


Of course running under wall power, we are not talking about a flashlight, but rather auxiliary lighting. It’s really outside the realm of what we do here.


I dunno what those heatsinks look like, specially interested in the ones you mentioned for less than $50 — do you have a link or 2?

Tisis Core edition, $48

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CNCman wrote:
This is a review of the Astrolux MF05 Flashlight and it is compared to the GT90. You cannot tell the difference in the video beam shots !! The GT90 is on the left. . https://www.youtube.com/watch?v=D5FGsnscboE . . . . .

Interesting stuff!
I barely use my GT90, but i’m still super happy with it.

1Lumen.com reports a noticeable difference in output between the GT90 and MF05 though, so it might be that in real life the difference is barely noticeable.
Another reason to stick with the GT90 Wink

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Robin Dobbie wrote:
Tom E wrote:

With qty 10 of XHP70.2's putting out a total of 25000 lumens, it would use about 150 watts.

Of course running under wall power, we are not talking about a flashlight, but rather auxiliary lighting. It's really outside the realm of what we do here.

I dunno what those heatsinks look like, specially interested in the ones you mentioned for less than $50 -- do you have a link or 2?

Tisis Core edition, $48

K, that thing is huge! --> https://www.raijintek.com/en/products_detail.php?ProductID=29#avideo

The radiator, thin metal design, and the heat pipes should be something that works well for LED's, but dunno if the watt rating is with or without the fans. If is was shaped and sized as something to fit a flashlight, might be interesting.

I'm thinking a massive size head of 120-150 mm or so, with 10 XHP70.2's so 10 mini reflectors. The LED mounts will be fairly close up to the bezel, therefore you got a lot of potential room behind the LED mounting plate to fit a sizable heatsink. Then the cell pack should be rectangular with a handle. So I'm envisioning an old style carry, like a Maxabeam, but more of a flooder than thrower.

 

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Yeah they’re huge, that’s the 15CM box design djozz’s talking about.

With those fins so tightly packed it would probably be good for less than 100W fanless. It’s an option as compared to the Noctua kit simply because it’s available without fans, and you can then buy the IP67 Noctua fan separately for just another $30.

It would need some sort of exoskeleton for strength because those thin fins are pretty dainty. Yet, like the Noctua, the fins are soldered.

What kind of cd/lm ratio are you thinking of with the 70.2s? Best I could find were TIRs with sadly low numbers. I’m probably not as resourceful as some people here, however.

I was thinking flooder as well, but not a mule or anything like that. I think some decent directionality and a bit of a hotspot is achievable with large COBs. Ledil has some architectural reflectors that can be bought at good prices in single quantities from Digikey and the likes. But there’s also these:

They sell them on amazon for like $30, or in a 3-pack on their site for $60-something. Would require a custom mount. Kinda a PIA, but with a rotary tool and a drill and some scrap metal… Then again the Ledils and proper LED holders everything would theoretically just snap and screw together.

With the COB option, the cost is far lower because you just have one $20 or $30 piece. How much is 10× 70.2s? I couldn’t find them for less than $12 – $15.

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A COB is an option, though not familiar with the specs or efficiency (lms/watt). I chose the XHP70.2 more because of the efficiency at lower amps, not so much cost.

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I think a good starting point is this baddy

Still over 140lm/watt at 200W at 85C, which with a good heatsink should be a good bit cooler than that.

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Think the XHP70.2 P2 at 2.5 amps each is like 177 lumens/watt, using TA's sig line link to the XHP70.2 P2 output tests.

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How well would a heat spreader work to keep all the emitters cool as spread out as they’d have to be? Still an extra $150-ish that could go towards cells and the heatsink/fan. I dunno, would potentially be shorter, though.

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