I appreciate that article. That’s what I meant, that the Melatonin hasn’t been proven. I’ve had so many people attack with articles that I don’t even explain myself anymore and just give the disclaimer I gave and tell how I’ve had excellent results.
It’s great, isn’t it! That is where we have noticed a difference, also. At night… You can actually continue seeing the stars after maintaining red light to walk where you are going…
It depends on the task, I believe. From several hours studying the topic a while ago, my unofficial conclusion was it makes sense to stick with low intensity white for most general tasks, because among other factors, most scenes are not monochromatic. On the other hand, if you needed higher acuity, because that requires a higher intensity of light - enough to shift from scotopic vision to mesopic or perhaps photopic vision utilizing the higher resolution cone cells - it appeared to me there is benefit in using red light.
At the intensities where good visual discrimination such as for reading or fast perception of motion is needed, white light may cause more melanin suppression or loss of dark adaptation (rod bleaching) than red light. On the other hand, red light also provides no color discrimination. There’s still a tradeoff.
I’ve been meaning to revisit this in detail again, keep track of sources, and write up a general summary, but time hasn’t allowed this.
Depends on the LEDs configuration, we might still be able to offer 1 or 2 pcs cyan version KR4,
please send us an email to contact@intl-outdoor.com
Shipping is not affected by Shanghai lockdown
Thanks for the fast email reply. I will place order accordingly.
This is the reason why we love Hank, right?
One, of many reasons! : )
Can’t wait to see some dedomed 519As in the KR4! Which driver would theoretically hold a higher sustained output with 519As on the KR4? The regular 5amp linear or the 2amp boost?
The boost driver will always allow for higher sustained output than the stock linear+FET driver, regardless of the LED’s you choose.
Does anyone have candela measurements of the D4SV2 with the LH351D LEDs and stock optics? I’m considering an all LH351D D4SV2 with the boost driver, since that seems like it would be the most efficient setup that still has a moderately high CRI (granted the 519A won’t be far behind when that comes out). I’m curious what kind of CD/Lumen I might see out of that.
I see, thanks; and this is just because the boost driver is more efficient at 2a mps or less than the linear at 2 amps or less, so less heat on the small host? Assuming the leds were in a massive host that can take the heat though, the linear at 5amps would have a higher sustained output then?
It is better to think of the boost driver as an 8A driver. Hank has said it’s 2A per LED with 4 LEDs, vs. 5A total for the linear driver (although there are also 7.5 and 9A linear drivers).
The main idea is correct though. With the linear drivers (or FET) the lost in efficiency is converted directly into heat, which limits the sustained (but not peak) brightness by adding to the heat load on the host.
Thanks!
I should just add for completeness the reason it’s quoted as 2A not 8A is because the LEDs are in series in the boost driver. The boost driver works by increasing the voltage to say 12V and driving up to 2A through the circuit, and then relies on the LEDs being in series to create an appropriate voltage drop across the circuit (each LED gets the 2A of current flowing through it, but only a part of the total voltage drop). The 5/7.5/9A drivers have the LEDs in parallel so they share the current the driver is giving them. There are likely a lot of electrical engineering subtleties, but that’s my simplified way of understanding it.
Output should be measured in watts. But manufacturers not doing this for some reason. Only advertising mooore low cri lumens 
I haven’t seen “watts” on a flashlight since my dad and I were looking at those Brinkmans in the camping section of Walmart back in 1994. Don’t hold me to that year, I’ve slept a lot since then!
Light output shouldn’t be measured in watts, but power input and output should.
The boost driver at its highest output should be consuming about 26W and putting out about 24W (claimed efficiency is 90-95). The 5A linear driver should consume about 5A * 4V = 20W on a full battery, accounting for voltage sag. Four 519As in parallel don’t need 4V for 5A though; they need 3, so the output is 5A * 3V = 15W. That’s 75 efficient.
My kr1 gt fc40 3000k is absolutely one of my favorite lights!
also the dm1.12 I installed xpl-hi 4000k into is as well!
and some shorts including dm11 sbt90.2 !
So approximately what % increases in sustained brightness (once thermal limiting comes into play) should we be expecting with the boost driver compared to the linear/FET driver?