30 seconds to first step-down? Unequivocally? So a week (or so) ago, in the Northeast US, at –35ºF ambient and with a strong wind, the light would still step down in 30 seconds?
Devil’s advocate…
I hope I did not misunderstand your post 
there is no 30s hard limit. I used my D4 in the snow some days ago, no stepdown at all because I dipped it in the snow every now and then
its purely dependent on temps.
Oh, I’m very well familiar with where the limits are… was just saying that there are variables, that’s all. 
Basically pulling TK’s chain as it were. lol Different ambient temperatures, different humidity levels, different wind levels, a different grip on the light… a lot of things come into play as to just exactly how long Turbo will go before stepping down if it steps down at all. She’s right though, of course, in most cases it steps down pretty quickly…
she said under 30s though
Which probably and comfortably covers 90%+
My D4 Titanium is in short body form, with an Aspire 18350 and Samsung LH351D 80 CRI 5000K emitters. I KNOW it’s going to heat up fast in Turbo, so I don’t use Turbo much at all. I have bigger more powerful lights if I think that level of output is going to be needed. I also have Anduril flashed so I can limit the ramp ceiling to a reasonable level without having to think about it in use. A double click changes everything of course, whole new ball game….
Edit: As an aside, my green D4 is also in short body format, with green output XP-E2 emitters. I had thought that these emitters would not pull enough to heat up strongly but boy was I wrong! Tint shifts very noticeably on the green output and heat comes in hard and fast in Turbo so again, I have Anduril ramp ceiling set relatively low and just seldom double click into Turbo.
I have one of my D4 with 219b and Anduril, and as you say, without the ceiling these run into thermal problems way too fast. So no IMR for this one 
oh oh…buy or not to buy:))
This picture kills me. It reminds me of mama, papa and little one…and one of the adults needs to get on a serious diet plan.
Curious…I like the flood of all those emitters right up to the glass but I’m curious, has anyone done the same thing with a much bigger light?
You want lamps that heat up fast? Get the Nicha’s. LOL. I have them and while they are nice they get hot way to fast.
The Astrolux MF01 has 18 emitters with similar optics.
Yeah, there have been many “shower head” lights in the past. I had one that used 21 led’s… wasn’t impressive with XM-L T6’s but with XP-E2 Torch emitters it was pretty cool!
Of more recent vintage, look at the Sofirn SF22. 18 XM-L T6’s. BIG light!
This one has a hollow head though, albeit the aluminum that is there is quite thick. Been thinking about remedying this but have yet to do so. Again though, if you push a lot of LED’s even semi hard then the heat is once again a force to be reckoned with.
Edit: My Bad! The SF-22 came with XM-L2 emitters…
is it a big difference frosted and clean optic?
It can be vresto, the frosted version acts as a diffuser and merges artifacts and/or dark shadows like a donut hole from a multi-die emitter or whatever, and typically this frosted application costs some lumens in output. I’ve seen a wide frosted CUTE-3 rob 1100 lumens from a triple X6 I built for a bicyclist.
So when are these going to be available with Aux leds like the D4S? They would sell a boatload.
Actually, the Vf does come into play in regulated modes. A lower Vf will allow the regulator to maintain operation for longer as battery voltage decreases. In order to stay in regulation, the battery voltage must exceed Vf plus the dropout voltage of the regulator chip. So even though the current consumption is Vf-independent when in regulation, the lower-Vf combination will “last longer” in regulated mode.
^
If you continue reading you will see that I admitted my error about a month ago, and the conversation went on. And I concluded (yet to be refuted) at the current levels that we were talking about for that emitter, that the diode voltage did not really matter. Unless you plan to run the battery below 3V.
That really was a fun discussion, at least for me.
https://imgur.com/BNVlWt9 Just looked at my emitters today and one of my LEDs is barely working. There’s a slight bit of light coming out but it’s significantly reduced. Is it a issue with the emitter or the main driver itself?
@nastynate : it is the emitter as they are all wired in parallel. So something happened that raised the VF of the LED above the rest so it doesn’t get a fair share of current. I guess it could come from a poor solder joint under the LED which adds resistance only to that LED. It might start to come on at higher currents which will raise the VF of the other LEDs but you will still have less light output, but less heat and current as well.
@Cpeng so I guess I’ll just keep using it as is for now if it’s not going to hurt the light overall. How hard is an emitter swap to do? I guess if another goes out I could always Try to swap them out for some lower temperature emitters.
@nastynate : Honestly I haven’t ever done an emitter swap, or reflowed an LED (but I have soldered surface mount and through hole many times). But I would first try to reflow the LED to the board with hot air or a hot plate. A hot plate would relfow all 4 leds at once but if you have flux I think it will work fine. You would have to remove the MCPCB from the light by de-soldering the wires with an iron. There are a lot of you tube videos that show this. If it was me I would keep using it, and buy another one. Honestly its cheaper for me to buy another flash light then to get all the tools together to fix my own.