Hello all. I do not post much but I am on here quite a bit reading other people’s progress and I have learned most of what I know almost exclusively through BLF.
Just thought I would let you all know what project I’m working on since it seems like I might be breaking some ground here.
My name has gotten out a little in the community with a few of the lights I’ve put together, nothing crazy (well except for my MTG-2 Maglite), just a few C8s, dedomed stuff, etc. Anyway, a local cop wanted me to build him a light after showing him one I had made, except he wants it in blue.
He wanted
Smallish form factor
Pocket clip
18650 style (rechargeables were a novel idea to him)
bright (duh)
royal blue
strobe
I thought I would try to dedome and de-phosphor an XML. I heard that acetone eats the phosphor layer, but that didn’t work for me. It de-domed the led nicely, but refused to take anything else off. I tried paint and varnish remover but that did nothing either.
So what led will work with XML current, is a similar size, and is BLUE?
I searched digikey, and came up with a Luxeon M emitter. I can’t find any info about that emitter on here, so that’s why I’m posting. It is a quad-die, and its maximum rated drive current is 4.2 amps I believe. So I found my blue led, what about MPCB? I searched around for that too, and decided to contact the people at Sinkpad. One of the sales reps is sending me 3 MPCBs free of charge! I was impressed. Unfortunately they are aluminum, as they never have made MPCB for the Luxeon M in copper. But I think it should do the trick.
The plan is to mate the led to one of Richard’s FET drivers, and use one of the strobe modes.
Sounds like a fun project. Is this the emitter you chose? You may want to consider using a Qlite instead of a FET driver. I’m no led expert, but going by this graph I think a FET might blow your emitter.
That was something that had me a little nervous too, honestly. Maybe I should go that route instead, especially since the MPCB is aluminum.
I’m not sure my multimeter works up to par, but I’ve never seen much higher than 3-4 amps direct driving an XML. Is something way off? Do thicker DMM wires make that much difference?
You might ask what use he wants to make of this —- a floodlight, to light up an area the way the police lights on his car do, as a signal of police activity?
Or as a spotlight meant to dazzle and blind someone? (He might do better with a cool white light, because the visual system isn’t particularly sensitive to the blue end of the spectrum — it takes a lot more photons to see something illuminated in royal blue than to see the same thing illuminated in, say, green (or white) light.)
The XM-L has a much higher Vf, so as the amperage goes up the Vf climbs, and at the same time the battery voltage is dropping under load. At a certain point the graphs cross and that’s as high has the XM-L will draw. It’s a coincidence that makes our 18650’s perfect for driving Cree emitters. The Vf on the Luxeon is much lower so I don’t think the graphs would ever cross. The emitter will just pull more and more current from the battery until it blows up.So i think you need a linear driver to limit it a bit.
You’re right, but the OP might want to look into the effects of that on the eyes. There is some debate that an emitter with the phosphor removed might emit a lot of nasty IR light. I haven’t done much research on it myself
High power blue would not safe to use to “dazzle” anyone. He would leave himself and his department open to problems, even lawsuits.
White is good enough, no need to go blue. Seriously, I’d reconsider building this for him. There is little good reason to use a high power blue light and it will be dangerous to the eyes. Even if not used to dazzle.
I do realize that blue light can be harmful to the eyes, but all I am is doing what he asked. I’m not going to tell him he shouldn’t have the light he wants because it isn’t safe.
He said he wants to use it to alert traffic, just like his light bar does. (Those have blue leds right?) Also he said it would be useful to find blood. As far as the strobe goes, that will be used in self-defense to dazzle someone.
I guess I don’t look at it any differently than a police using any other kind of self-defense method, such as a taser, baton, etc.
I’m planning to use the Luxeon M rather than a blue XML. I don’t think I would have lots of confidence in the longevity of the XML after scraping on it. Also, I would rather use a proper blue led with a known wavelength.
Is it really that more dangerous than with the phosphor on?
My understanding is the phosphor itself isn’t a filter. It doesn’t get rid of all the blue that hits it. It merely absorbs some of it and then fluoresces red and green, which combines with transmitted blue to form white.
I would say inform him of the risks, then if he still wants it go ahead and build it. He might be completely oblivious to the dangers of blue light, even to his own vision.
The phosphor reduces the amount of blue but more importantly it add a spectrum of other colors. Blue wavelengths look dim to our eyes (vs other colors at same power), less pupil constriction (more light gets to your retina), less blink reflex, less urge to shield your eyes.
Also the other colors mixed in help bleach the photoreceptors so that they can recover.
A red or amber light could catch people’s attention just as well as blue.
Bottom line: it’s a crazy new world. You can buy 405nm “violet” lasers for under $10, and they can do permanent eye damage in less time than it takes for your pupil to contract and your eyes to blink. And that timing is because 405nm looks like a very faint purple color, our eyes are barely sensitive to it for vision. It doesn’t make us look away — yet it can permanently damage your vision.
I find myself wondering, if I were an armed peace officer and someone lit me up with one of those blue-violet lights, and I thought it might be bright enough to permanently blind me — what would I do?
