Complete custom tac light

Hey folks,

I’m a machinist, I design and make a lot of stuff in my free time. With sticker shock and disappointment of lack of features on ready to mount flash light solutions, I ended up here.

Firstly: I plan on using a single 18650 battery. I’ve read that the power density is the best for size. Along with being one of the most widespread types of batteries, it will also fit my design quite well. This a complete from the ground up build. I am not interested in buying or retro-fitting an off the shelf item. I have a specific design in mind.

Secondly: I am struggling to come to a conclusion when it comes to drivers and LED options. I looked into XHP70.2 for the LED because I was impressed with the lumen ability and wide area the LED illuminates. Ive looked at drivers from Ali, MTN, and Convoy. There are so many options its overwhelming. I don’t need to program something elaborate. I’m cool with a 5 mode driver that is already programmed, but I am more than willing to program a driver to get it just right.

Thirdly: My biggest concerns are moderate battery life at a medium level and the ability to have a insane turbo mode/High strobe in a pinch.

So far the XHP70.2 is looking good to me but I am willing to change if it means I can also be more compact. I am confined to an 18650 because it will be what fits best in my hand. If anyone has any other suggestions for a driver I would greatly appreciate it.

Bonus: If you can lead me in the right direction, I will send you a complete light free of charge it will be made entirely out of 6061 aluminum.

3 Thanks

Thanks for joining the party, d.i.r.t!
I would suggest using a 21700 cell.
They have better power density than 18650 cells.
Also, I suggest using an XHP70.3 HI emitter.
That’s a better emitter than the XHP70.2, and it throws better.

2 Thanks

Thanks @raccoon! I could change what I have to accommodate a 21700. I looked at the 70.3 and the 70.2. I see how the throw could definitely be of benefit in this application. I bet the 21700 would be a better pairing in this situation as well.

2 Thanks

By the way, if you’re looking for throw, I would suggest the SFT40 emitter.
It’s not as bright as the XHP70.3 HI, but it throws way further.
If the SFT40 throws further than you need, you could consider the SFT70 emitter.
It provides more flood, but at the expense of throw.
The SFT70 isn’t very popular, though I prefer it.
The SFT40 is super popular because it’s the most practical throwy emitter that provides some usable spill.

3 Thanks

Was about to say just this. The XHP70 is too large of an emitter to be driven by a single 18650/21700 cell sustainably. And its throw will be very weak, so a lot more battery consumption is required to light up an object to the same brightness as a smaller, more throwy emitter.

For the OP: do you have approximate dimensions in mind for the light, and do you plan to use a reflector or TIR? If you tell us what kind of beam profile you are looking for, we can suggest a good LED+optic combination.

3 Thanks

I’m not so sure about that, but I do agree with the rest of your post. :+1:

1 Thank

To clarify my comment: by “sustainably”, I mean to a decent portion of its maximum output. If near-maximum output is not achievable or sustainable, it is often a good idea to step down to a smaller LED, whose near-max output is attainable. This results in at most a few percentage points loss in overall output, but can often double/triple the throw (intensity), if not more.

2 Thanks

:grin:

1 Thank

Yeh, the problem with “maximising” output is the inverted parabola of the emitter’s output. Once you climb up that curve, output flattens out and even decreases, so you could push twice the current (and thus power and heat) through the beastie to only get, say, 10% more lemons on the output.

Me personally, I try to not go higher than halfway up that parabola. Want more output, use multiple emitters, etc.

The TIR lens of the IF22A is pretty clean. Lots of throw with just enough leakage (“spill”) to not wash out what’s right in front of you.

2 Thanks

For the purpose of building a flooder that maximizes efficiency and output, I agree with your analysis. However, to achieve good throw in a compact size, high flux density must be achieved at the emitter, which makes climbing the parabola necessary. A good rule of thumb is to max out the light at 80% the power where the LED achieves maximum output; one gets over 90% the maximum output in return.

For a sense of scale, the XHP70.3 HI maxes out at 40A 3V equivalent. A compact 21700 light cannot output anywhere near even half of that without overheating immediately. Assuming that 10A@3V is sustainable (which is extremely generous even in cold weather), we are looking at 3839 lumens with intensity 52.6 cd/mm^2. In comparison, the SFT70 achieves 2991lm with with 133.6 cd/mm^2. So this change loses 22% output (not noticeable without a side by side comparison), but gains +154% (i.e., more than doubles) intensity.

For sustained output, the current will be lower, which further favors the smaller emitter. At a more manageable 5A@3V, the output gap goes down to -14%, while the intensity gap increases to +181%, almost tripling.

5 Thanks

Excellent!
Do you happen to have the stats for the SFT70 vs. the SFT40?
(I’ve always wondered how much throw is lost with the SFT70 compared to the SFT40.) :upside_down_face:

3 Thanks

Yeh, that insane current is why people chance sticking cells in series, like my 1S/2S L2 (wow, been ages since I touched that!) or the 4S Haikelite I got somewhere.

Quad the voltage to quarter the current…

2 Thanks

User koef3 here has tested both 6500K and 3000K variants of both SFT emitters, I’m quoting his specs for 6500K.

Given the same drive current (keeping in mind the 6V/3V difference between SFT70/40), the test results suggest that the SFT70 is slightly more intense (by no more than 5%) below 5A, which is a surprising result. Above 5A, the SFT40 pulls ahead. When both are driven to maximum, the SFT40 is 30% more intense.

2 Thanks

The actual dimensions of the light? I’d like to keep the TIR/Reflector around 1 inch in diameter + or - .250. Like I said this is a ground up design. I’m in the planning phase. Once I have rough dimensions of the actual hardware I will begin to finalize the dimensions. If this helps it will be for night time use, 50 yards max. I want to be able to blind someone in an entry way of a house or in a small backyard. This light would only need to be effective in a close quarters scenario. So like I was saying, throw isn’t nearly as important. So I’d say, at no more than 20-30 ft I’d like to be able to shine this and absolutely bamboozle someone. I did plan to use a reflector, but if there is an emitter that would give me that range I could forgo the reflector entirely. From what I’ve seen the Emisar D4V2 may be really close as a reference.

This is the info I’m looking for. I don’t have a good frame of reference when it comes to comparing the LEDs.

I also didn’t know the difference between a TIR and a reflector. I figured those two thing would’ve been more broadly categorized under a reflector.

Thank you for the detailed info! Extremely helpful in narrowing things down.

Sub-1 inch diameter is pretty standard for single 18560/21700 lights.

Throw is quite important for this purpose. A light that does ANSI 50 yards does NOT stay at a constant high intensity for all of 50 yards and then sudden cut out; rather, its intensity decays continuously over distance, and at 50 yards is as bright as moonlight, which is useless for disorientation. In other words: for two lights that can both reach over 50 yards, the one with more distance gives you more intensity (and thus more blinding power) at 50 yards.

For the purpose of disorientation, the beam needs to be simultaneously (1) intense for disorientation, and (2) wide for coverage and ease of aiming. These two requirements are in a tradeoff with each other, so you need to decide what’s a good balance. What beam angle would be good for you?

Forgoing the reflector entirely would not do; a reflector easily duplicates the intensity by anywhere between a few dozen times to a few thousand times. For the size of a D4V2, it is possible to build a light that simultaneously throws and floods better–the quad LED setup is very poor for throw.

Here’s a thread with more info about the LEDs. I personally use the tests by koef3 because he is still an active LED tester, which makes comparisons consistent. Basic data for popular flashlight LEDs summarised

A reflector and a TIR produce completely different beam profiles. A reflector gives a hotspot, 60-ish degree spill, and then abrupt cutoff. TIR tends to have a larger hotspot, and the spill is dimmer but wider. Here’s an example of a reflector and TIR in the same light (approximately your size) and same emitter, LH351D (which is on the floody, i.e., not very intense, side). Source.

1 Thank

Hi @d.i.r.t , welcome, i’d like to contribute a few things especially when i read the reflector size… You may ask other fellow here for more details in calculation and technical.
I have certain preferences for the CONVOY S11 reflectors,
(hope in the future @Simon_Mao provide this configuration, S11 head with 21700& 18650 tube)

Here’s a link to a review by @L.R.O , this showcase the xhp70.2 and the xhp50.2 in a S11 ( Note that with the .3 HI version the intensity would be higher)

Cheers :flashlight:

3 Thanks

I vote for SFT70 too :star_struck:

1 Thank

It’s hard for me to tell you a specific angle. I found a great video where it looks like the SFT70 with OP is going to be exactly what I am looking for.

The comparison between these two is awesome. Here this guy uses an orange peel reflector and I like the dispersion of the light from the SFT70 in this case. So a wider angle would definitely be more of what I want.

1 Thank