The effectiveness of slicing is sensitive to the thickness of silicone remaining over the die. If it’s not very thin light can reflect off the silicone/air interface and bounce down to the side of the die where it’s more likely to be lost. This reduces the output and reduces the throw gain. If the silicone is very thin this reflecting light will bounce back to the die where it increases the die luminance.
With some of these LEDs the bond wires are tall which makes it harder to get a close cut.
A theory: the reason that by slicing a warm/high CRI led you loose so much output (20+% compared to 10% for cool white)is that there is much less blue light to be recycled to turn into more visible green, and at the same time phosfors are present that recycle green into less visible red.
I have not fully thought this over, but I have seen with the spectrometer that when a high CRI led is illuminated with 530nm green light, apart from scattered green you can measure some red coming off the led.
I discovered that after a couple more attempts. Shaving it so thin I accidentally took off a bit of phosphor on one edge got me up to 715m throw. As you know from your own attempts you need to give the bond wires a wide berth because they stick up so much, and I’ve managed to ruin two that way so far. Working on #4 right now; wish I ordered more than 10 of these!
In any case this is a very promising LED for a high CRI thrower. 600m throw to start is quite acceptable, and increasing that another 100m with a rosier tint is the icing on the cake. I think it’s just a matter of grabbing half a dozen and trying for the best slice possible.
Slice #4 got me 670m throw with no damage to the phosphor, which I’m quite happy with. It has always bothered me that no matter how many boutique high CRI modded lights I carry, I’m still stuck with a CRI 70 thrower that washes out everything in nature. This SST-20 is throwing just as well as the stock XP-L HI and looks way better out on the trail. I look forward to acquiring a nice tint bin in 4000K which will match my other lights better and probably throw even further. Next up is seeing whether it can handle a VTC6 when it’s pulling 5.5A off a GA, but I’ll be using the trimmed phosphor sample for that!
Here’s the first bond wire that melted if anyone’s interested.
I tested a SST20 5000k in a C8+ at 2.8A and measured 550m throw (less than the stock xpl hi)
Then put a SST20-W 4000k and a LD-A4 driver at 5A: I measured 500m throw
the 4000k needs 2A more and still throws less than the 5000k, a XPL-HI V2 5D will outthrow the 4000k SST-20
Maybe I’m not paying attention to CRI but is it worth to lose such amount of light for a better CRI? the LH351Ds are 90CRI and are similar in brightness to the XPL/XPL2
Going over 90CRI with good tint costs you at least 40% output compaired to a low CRI cool white version of the same led. This is also mostly true for the LH351D, but that is just a very high output led because of the very large die, low CRI versions of the LH351D have even more output. They did cheat a bit with the high CRI LH351D, the CRI standard is not ideally defined, so you can get away with putting too much green in the spectrum (green light contributes maximal to output measured in lumen) without loss of CRI. So many the high CRI leds have an ugly greenish tint while measuring a great CRI.
And yes, very high CRI is the big thing about the 4000K and 3000K SST-20. How you like that is a very personal thing. If you are in the habit of chasing crooks around the block, I assume that high CRI is wasted on you, but in nature hikes I can imagine high CRI being pleasant enough to give in some lumens.
I found that my ability to tell trail features apart (in that case: leaves vs. rocks) was significantly hampered with a CRI70 light. Since then I’m a big proponent of going higher than that.
At the same time I’m not convinced that more than 80 would be worth it for me.
This is a rare attitude, most tend to prefer either 70 or 90. Not having an intermediate choice I tend to go with the Hi-CRI people and pick 90+. But I’m not really happy about the lumen loss…
*70CRI for me is always too ugly to accept, with a soft spot for the 4000K Luxeon V because of the superb tint
*80CRI is great for outdoors, beyond 80CRI the tint is of more importance than increasing the CRI to 90
*90CRI is for EDC, where output and throw are less imprtant than a pleasant illumination close-by.
I think with all this new led recently, do you think it make sense for someone who have good knowledge of market to make a clear list of the best high cri led on market today, and best tint close to black body radiation? I think this sst20 and nichia 219b(v2?) and clemence nichia led (which one? e21?) have best performance so far, but good to make list somewhere and put on sticky?
There are just too many variables. The nichia e21/optisolis are lower power, super high cri but picky about optics and require special mcpcb. sst20 varies a lot based on current, low current = above bbl, high current = close to or below bbl. 219b is unobtainable but also shifts far below bbl with high current but at least it starts out close.
There is still Samsung (above bbl often, sometimes not much above, super high output), Cree (XM-L mostly or diffused), Luxeon (MZ, diffused, super high output)
I don’t notice the downward BBL shift on my SST-20’s that much, but it is there. When I run my quad emitter M2 in direct drive at 4.5 amps per emitter, then I notice it, but most use cases don’t quite require me to drive my emitters quite that hard.