Accidental MTG2 dedoming.

“Ignorance is bliss” :).

As I said, I saw the OP, but then didn’t wait for the subsequent posts, mentioning about dedoming with gasoline not working. By that time, I had already punctured the dome and the emitter was in the gasoline, so I didn’t have much choice except to keep going, and hope for the best :).

As far as the phosphors, I don’t know. I’m not a tint expert, but the beam color doesn’t look terrible to me.

I have another MT-G2 light that still has its dome, and I compared them side-by-side, and the dedomed one looks less yellowish than the domed one… The beam from the dedomed MT-G2 looks more like a normal CW.

I’ll try to get a picture side-by-side, but I’m not sure my camera will render the colors correctly, but isn’t that backwards from expected?

Hi,

For comparison (camera check), here’s a normal stock el-cheapo XM-L T6 light:

and here’s a comparison of the non-de-domed MT-G2 light (on the left, bought from CPF) vs. the newly dedomed MT-G2 light (on the right, Shorty DST):

The only way I could take this was by standing both MT-G2 lights on a table and shooting at the ceiling. Plus, I couldn’t really get them much further apart. Sorry :(…

Also, FYI, I was able to get a lux measurement of the shorty DST with the dedomed MT-G2:

After dedome MT-G2: 36880 lux (36.88 Klux)

Before dedome MT-G2: 26851 lux (26.85 Klux)

Also, correcting something I said earlier, batteries were 2x18500 Sibeile IMRs. They are not fully-charged.

This is my experience as well, except that if you turn on an XMLU2 light next to it you'll probably notice it's a lot warmer, just cooler compared to the regular non dedomed MTG2.

I was just re-reading your earlier post, and saw that you had said that. Isn’t that weird? All of the stuff I had read was that dedoming caused the tint to get “warmer”, whereas with my dedomed MT-G2 and with yours, it got “colder”!

Edit: I’m still a little disappointed in the dedome though. I was hoping for much higher lux than I reported above, but it was not even close to 100% increase… more like less than 50% increase in lux.

Yup, I'm also surprised by this :D Personally I actually prefered the normal "warm" tint of the original.

Well, I’m topping up the 2 x 18500 Siebeles. They were only at 3.97V and 3.98V Also, tailcap current on the DST was only about 2.02 amps.

I’ve also move the DST pill “up” further towards the reflector, and I’ll test lux like that, after the batteries are fully-charged.

Also, remember, I have a 0.5 ohm resistor in the direct drive. I did that originally because I was worried about over-driving the MT-G2 :)!

I might think about trying to put another 0.5 ohm resistor in parallel, if I have the time, as there’s plenty of room in the DST’s pill, but I won’t be able to do that today/tonight, I think.

Edit:

With fully charged 2 x Siebele 18500 IMRs and moving the pill further towards the reflector, I got:

Tailcap current: 2.20 amps

Lux: 38010 (38 Klux)

So, current increased slightly, and lux went from 36.8 Klux to ~38 Klux. Not much improvement :(…

That’s much better tint than I expected. I expected royal blue, but that really doesn’t have too much purple in it. I’m impressed that that much phosphor can be removed and still have a useful tint.

I wonder how much the phosphor contributes to output. We need someone that knows more about this stuff to chime in.

I don’t know for sure, but I think that, maybe, one thing I did different was what, as I said, I was really concerned about leaving the emitter soaking for a really, really long time, based on some comments about the phosphor being “like paste”. I was really worried that if I just left it like that, all the phosphor would “drift off” (my mental picture).

That was why, when I got to the point of trying to get the larger clump of stuff off of the emitter, I didn’t just leave it in there, but pulled it out before I went off to my appointment, and also why I hesitate soaking it again now, to get that last tiny piece of stuff of off that one segment.

Again, I don’t know. I know others, including comfy, have said that they left XM-Ls in gasoline for weeks, but maybe the chemical composition of either the phosphor or the dome are different for the MT-G2s than for the older emitters like the XM-L?

All I know is what I did, which seemed to work “ok”, and hope what I documented helps others…

Yeah, I would call it a success. Many people prefer the tint you achieved. Especially, for throwers. I applaud your efforts and reporting. Good stuff. I hope you get that baby to 100% more throw.

Thanks.

I don’t know about that last thing though. I just was outside, comparing it to my STL-V6 with dedomed XM-L, and, even with the spill effect masking the throw, it was pretty clear that the STL-V6 spanked the DST :).

My last hope is adding the parallel 0.5 ohm resistor, but I kind of seriously doubt that’ll make up the difference. Would definitely be nice, but I’m kind of doubtful.

Based on djozz’s test results on severly overdriving the MT-G2 (It survived 16A), I think you can probably get rid of the resistor all together. Do it at your own risk, but I would try it if I had that setup. I think it will not go over 5A, maybe 6A and only for a short time as the cells drain.

Will do, but, not purposely being a “doubting Thomas”, but I think “lumens <> lux”.

Perhaps if you get a bigger reflector?

I just was thinking (it happens :)!): If the MT-G2 tint gets cooler when it’s dedomed, does that mean that lumens would increase, rather than decrease with a dedomed MT-G2?

If lumens increased, then why would the dome be on in the first place? :o

Slewflash. Im just guessing here but I’d say the dome is for 1) mechanical protection, 2) to produce a particular beam pattern.

The dome increases output on every LED. SST90, XPG (2), XML (2), XPE (2), XRE (2). After dedoming a drop in lumens is always observed, and I think Cree is aiming for maximum lumens/watt.
It would be highly irregular for the output to increase after dedoming, but at this point it seems kind of plausible since the tint shifted towards the cooler side of the spectrum instead of warmer like every other LED.

I think it’s unlikely the dome adds lumens to the output. I’m quite confident it’s a factor of where the light from the emitter goes. With a dome, it’s concentrated in approximately 100 deg range, without the dome, the light spreads 180 deg or more. I’m sure lumens drops only becaue the reflector can not catch all the light from the LED anymore.

I’ll bet with a mod where the LED is inside of the reflector (such as a maglite mod), as opposed to ‘at the base of the reflector’ there would be less of a lumens drop when the LED is de-domed.

Not sure I follow you on that one. If you increase the lumens and change nothing else, the throw will also increase.

Regarding the dome, it serves two purposes. The first, and most important to lighting engineers is beam pattern. The dome is actually a small lens. it focuses the light into a particular shape so someone making a light fixture optic/reflector can capture as much of the light possible and send it where they want it.
The second is emitter protection, also important.

scaru once explained lumen drop as a side-effect of additional reflector loss. Since photons exit the dedomed emitter surface at any angle up to 180 degrees, and not focused toward the front 100 or so degrees, more of them hit the reflector and go straight out to become part of the hotspot.
The problem is, photons that hit the reflector have a greater chance of being absorbed. Reflectors can eat around 15% of all light that hits them. This is bad for total output, but good for throw.

Yes, I ended up with a royal blue MTG2. This LED is built different. Look close and you can see the yellow phosphor is covering the entire round area under the dome, and not just on top of the dies. I think the phosphor is in the bottom layer of silicone and not attached to the die like on the others that survive de-doming with the phosphor intact.