testing a Samsung LH351B series 5000K 70CRI led

Flashlight Modding and DIY Parts
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I really have no idea where to obtain the newest generation of 3535 footprint Samsung leds (same goes for some promising LG leds), but led4power managed to get some samples of the highest bin of the LH351B series and sent them to me for testing. To immediately destroy any hope about this: he tried to dedome them and it did not go well. So leftover is some output testing to see how they keep up with the other latest leds that I have tested.

He sent me samples of the 5000K 70CRI type and the 4000K 80 CRI type. This test is of the 5000K 70CRI type. I did an output test and in the chart the results are compared to older tests results of similar 3535 footprint leds: the Cree XP-G2 S4 2B, the Cree XP-G3 S5 3-bin, the Nichia 219C 5000K 80CRI, and the 3rd gen. Osram Oslon Square 5000K 70CRI.

The test was done like all my more recent emitter tests. I described it in detail in my XP-L test. , with two minor differences that should not matter significantly for the results: I used my Integrating sphere no. II instead of no. I, and for the current I used a clamp meter, which appears to measure 0.1A lower than the power supply current-reading that I used before.

In summary: 1) just one led was tested, reflowed on a DTP copper board (XP-Noctigon 16mm) 2) I used my large version II integrating sphere with high quality luxmeter, 3) the output numbers and voltages were measured with the led close to 'steady state' for each current, so warmed up and settled, you should be able to get these numbers in a well heatsinked flashlight. Mind that these are output numbers of the bare led, in a flashlight there will be losses from light obstructions, lens and optic, 4) output is in 'djozz-lumen' defined as 1/550 of the output of my Sunwayman D40A on high setting, which I hope is close to the real lumen, but at least is consistent over all my emitter tests done in integrating spheres.

Here's the chart:

What can be seen:

*up to 1.5A the output is keeping up well with the other modern leds, but at higher currents the output dives firmly under the others. The thermal resistance of the Samsung as listed in the data-sheet is not significantly higher than the other leds (=4K/W , as opposed to 3.6 for the Oslon Square, 3 for the XP-G3, 4 for the XP-G2, 4.2 for the 219C), so I did not expect this.

(a possibilty for a test error is a bad reflow or mounting, but I checked before and after the test and I did not see any signs of that. I always reflow the leds that I test very carefully, at the right temperature and using a bit more solder paste than strictly needed to be sure that the led is connected well over the entire surface of the solder pads)

*the voltage of the led is conveniently low, but not as low as the newest leds from the other manufacturers.

Conclusion.

This newest Samsung LH351B led, (at least this sample and in this single test, testing a bad one is always a possibility) does not do anything better than the newest leds from other major manufacturers, but when used at low currents under 1.5A, it performs very decently. Perhaps if they become available for flashoholics community, the price could be attractive, and I did not check the tint, that may be particularly pleasant. I will try to build a triple at 4.5A with the 4000K 80CRI variant to get a feeling for that aspect, and report about it in this thread :-)

thanks for reading!

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Nice work again djozz. Thanks for taking the time and making the effort.Just a reminder to link it here.

You can kick me now. :slight_smile:

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This leds (as most other samsung and lg 3535s) are widely used in office lights (also called “Armstrong”) and much cheaper than other tested leds when buying in reels.

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Aye aye sir! Done. :slight_smile:

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No cri or tint advantage?

I never thought the xpg, 2 or 3, could compete with the xplhi, or xpl in a good reflector.

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The LH351B is mainly a very low cost high CRI small die LED.

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Thanks.
I don’t care about cost of the led too much, because I am not doing volume.

I am looking for the best lpw /cri balance. I might be thrilled with 80 cri, if Flux at 1 and 2 watts is astoundingly efficient enough. Naturally, a 90 cri would be better, but depends on luminance. 5000k is my gut preference. But would take anything 4000k to 6000k. I reserve my 3000 k preference for photography, cooking, eating, relaxing, and falling asleep.

What is the most tolerable cri, with the closest to 400 lumens (373lumens @700mA was my last build in 2016, 4000 candela) at 700 ma as possible, in 2019,for the standard 31 to 40 mm smo? I need to reach 4000 lux at 2 meter, minimum, at 700 ma maximum drive current.

What puzzles me, is that leds seem to be marching backwards in terms of efficiency. I am not even sure if the newer Xp-l2, with their higher cri are suitable in a smooth reflector, due to the rumored non uniform color in the beam… Intl-outdoor.com has lower bins than 2 years ago. Mountain are all low bins… I expected 220 or 240 lpw, neutral 5000k leds by now. Instead, I see lower lpw leds than 2 years ago. I see 4750 k Xp-l HD, but marketing fluff, no bin or cri listed. I am guessing DigiKey and reflow is my only option, right now. Reflow risk makes me nervous, but is satisfying if it works. DigiKey lists the cree part number, at least.

[Background, and useless prattle :

I don’t like the 219 that I own, as it is too inefficient for my needs. Every 10 or 15 percent means an hour runtime when the target is 10 hours. And a light that dies even a half hour shy of a full work day, costs money for a for profit operation.

My last builds were 2016. I decided to wait for better higher cri ish, higher efficiency leds than the 70 cri Xp-l 202 lpw 4000k v6 350 mA /373 lumens 700 mA of my last build, 2x18650 buckpuck 700 ma driver from ledsupply.

What puzzles myself, is that I bought some higher cri led and reflowed it, and dropped it into my craft bin’s led compartment. But I forget where I bought it.

I,getting the itch this month, put together two 21700 single cell builds using stuff I bought in 2016, I think. Mainly to test my taco shell 21700 body idea—melt plastic or aluminum over a 3/4 inch steel pipe with heat gun or blow torch for a right angle body, which the battery could be swapped if needed from the side…The result is a 45 or 50 gram light using the heat wilted plastic plus 23 mm tir, and, 85 g using thin aluminum (roof flashing, which turned out incredibly strong due to the arch physics). I added fiberglass covered in borax/borate fire proofing just over the positive.

This mystery high cri led seems to be putting out exa the same lumens at 700 ma as the 270 lumen at 700 ma lights.]