Yes, exactly. I'm probably not being very clear by trying to be brief. Approximately half of the light from the die (before or after down conversion) will be back scattered and re-absorbed by the die surface. Whatever else makes it back will suffer the same odds, plus the light is likely to be down converted to a wavelength not absorbed by the phosphors so it will be scattered (minus Fresnel loss). There are a ton of papers describing the efficiencies of phosphor down conversion and die modeling. This is a quick one that talks about back scatter and loss: http://lightingresearch.org/programs/solidstate/pdf/Zhu-SPIE6337.pdf
dedomed a xm-l with success
- Thread starter ergotelis
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Al Combs
Enlightened
- Joined
- Jul 2, 2007
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Clearly you guys have a better understanding of the nature of LED's than I do. Here is a picture from one of the threads I was thinking about. Saabluster had taken a picture of a Luminus CBT-90 at the same current level and exposure. The two pictures are with and without a Wavien recycling collar. The CBT-90 has no Lambertian dome, so the increased output and shift in color temperature must have been caused by some other factor(s). If not secondary fluorescence from a reflected blue ray of light, what is the cause?
Thanks for including the links in your post Al. Very helpful. Seven page thread, 11:30 at night. It's going to take a bit to digest all of that! At a glance I am only familiar with the Waiven optic via their patent info. I've not had a chance to mess with one. My first impression is that the optic is used to capture the emission for increased brightness (as opposed to increased output or making a change in the numerical aperture). Photos are nice but there's no substitute for hard data when it comes to assessing what's going on. I would be interested in data from a spectrometer and output measurements gathered using an integrating sphere to gage the extent of whatever changes were made.
ergotelis
Enlightened
I think it is good to post here some first results with other reflectors.
With trustfire x7 @3,5amp on the led, i got ~172,000 lux(!).Led is one of my crappy t6 with one of the 3 wires of the core cut.But still works!Before,on this host it was a xm-l U2 2S performing ~100,000 lux.
By the way, what is the record of lux number with a led?
On a trusfire C8 classic host with the 41mm widex31mm height smooth reflector, i got@ 2,7amp about 48000 lux. Owned my catapult v2 xm-l(!!!). Led is T6 3S with very few defects on the core.
Till now, i have only dedomed 3 leds, 2 were ok on the one i got a wire cut, but still works,don't know if and how it affects its performance. Will see. The method as i said is at a good heat level of 150-180 C, to press gently the dome with tweezers from left and right of the wires and not close to them(we should not press the dome on the point where the wires are on the core).It will pop out after some time almost easily. But remember, this only for real crazy modders and those who don't have problem to waste their mine(well it is not fine to waste your money but i am maybe a lot more crazy)
Currently, trying to measure the lumen loss.
With trustfire x7 @3,5amp on the led, i got ~172,000 lux(!).Led is one of my crappy t6 with one of the 3 wires of the core cut.But still works!Before,on this host it was a xm-l U2 2S performing ~100,000 lux.
By the way, what is the record of lux number with a led?
On a trusfire C8 classic host with the 41mm widex31mm height smooth reflector, i got@ 2,7amp about 48000 lux. Owned my catapult v2 xm-l(!!!). Led is T6 3S with very few defects on the core.
Till now, i have only dedomed 3 leds, 2 were ok on the one i got a wire cut, but still works,don't know if and how it affects its performance. Will see. The method as i said is at a good heat level of 150-180 C, to press gently the dome with tweezers from left and right of the wires and not close to them(we should not press the dome on the point where the wires are on the core).It will pop out after some time almost easily. But remember, this only for real crazy modders and those who don't have problem to waste their mine(well it is not fine to waste your money but i am maybe a lot more crazy)
Currently, trying to measure the lumen loss.
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Walterk
Enlightened
I got 2.100.000 cd with a single led.
But it means nothing for comparison, thats why I hope you would measure the Lux@ 1 meter without any reflector, tir or lens.
Because only with that measurement you can calculate the surface brightness of the modified led.
(If you have measured same set-up @1meter without optics before modding, then you really can tell its effect on throw....)
can you share the pic?
Walterk
Enlightened
How did the experiment work out?
You still like the de-domed XM-L?
Does it hold, or is the silicongel or phosphor acting up?
You still like the de-domed XM-L?
Does it hold, or is the silicongel or phosphor acting up?
The phosphor seems to hold up for me. I dedomed the LEDs in the latest LR+. I have destroyed a little less than half of the LEDs that I attempted to dedome. Sometimes it is the bond wires and other times it is the phosphor pulling up. Can be quite a nightmare. It does drastically increase performance though.
easilyled
Flashaholic
To be pedantic, I'd say that it drastically increases throw rather than performance.
Since the total output is actually decreased after dedoming, I don't think its correct to use the word performance.
Walterk
Enlightened
Yes we know, well I know from beamshots and experiences shared on CPF.
Talking only about the witnessed drop in lumen, please be clear on where it comes from:
Isn't it that the same lumen are emitted, but only in a viewingangle that is hard to collect by most reflectors and optics?
(And thus most experiments so far have improved throw but not lumen)
So we should regard dedomed led not anymore as an ' almost-point-source ' and thus have to look for an other lenssystem to maintain lumen...
I think dedoming invites to step off the straightforward aspheric, and think more like MegaRay and other light projection lenssystems.
Or using smaller diameter (led filling more of the aperture of the whole lens), multiple lenses like described in the Ledlenser.
ergotelis
Enlightened
I own you some photos and beamshots , sorry for not having already done this. On program it is to go out tomorrow in the same place i had taken some beamshots in the past, to show you how a dedomed led performs, among with other famous flashlights.
In general, a dedomed led has almost double the hotspot lux in the same reflector, but with a performance drop of 20-30%.
I will take beamshots of a dedomed P60 host (Xeno F8V5) and a Trustfire X7 dedomed xm-l mod.
I will include some very popular flashlights and another interesting mod, a Armytek Predator with a XT-E R5(from cutter) led.
I have another dedomed xm-l led(other than the first two mentioned), it is currently in a cheap trustfire 40mm host(of $12), i will include that too, just to show that in a very cheap setup you can get crazy lux numbers.
In general, a dedomed led has almost double the hotspot lux in the same reflector, but with a performance drop of 20-30%.
I will take beamshots of a dedomed P60 host (Xeno F8V5) and a Trustfire X7 dedomed xm-l mod.
I will include some very popular flashlights and another interesting mod, a Armytek Predator with a XT-E R5(from cutter) led.
I have another dedomed xm-l led(other than the first two mentioned), it is currently in a cheap trustfire 40mm host(of $12), i will include that too, just to show that in a very cheap setup you can get crazy lux numbers.
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"Increased performance" is a perfectly acceptable term to use to describe the effect of removing the dome. Well perfectly acceptable given it is said in context. Context which I did not provide so I am glad you mention it lest we get people thinking dedoming creates more lumens.
Thanks
The same lumens are not emitted.
The dome does two things that improve light extraction. It provides a more gentle transition in index of refraction which reduces reflection losses. They actually use silicones of varying indices going from higher index materials close to the die to lower index silicone as you move out away from the LED die. The LED die has a very high index of refraction and without this gentle transition more light would stay inside.
The other thing the dome does is move the escape surfaces farther away where the angle the light can escape the package is more perpendicular. Light transmission through materials of differing indices happens most efficiently with the light at a 90% angle to the refractive surface. The more you diverge from that the more that will be reflected internally. LED manufacturers could actually improve the performance(lumens) of their current LEDs by doing nothing more than making the dome larger. They of course also have other things like cost to factor into the equation.
bshanahan14rulz
Flashlight Enthusiast
SaabLuster, could you tell if the phosphor was suspended in silicone too, or if it might have been a different material? Perhaps a solvent or digester ought to be researched. The Nichia (not a cree, but I don't think I've seen this type of info on a cree DS) datasheet I have actually tells what the different parts' substrate materials are, generically, i.e. dome is silicone (doesn't say what it's doped with, or if it even HAS any additives), phosphor layer is phosphor suspended in silicone.
Walterk
Enlightened
Don't be sorry, its nice you show your experiences. When you take beamshots, could you make a white-wall beamshot with a dedomed led without reflector/lens, so we can see how the light distribution has changed?!
Thanks for the clear write up, I expected almost same lumen.
ergotelis
Enlightened
I had promised to do the beamshots but i didn't , i am planning to go out tomorrow for this.
If i understood well, you need two beamshots, from a dedomed xm-l led and a normal xm-l , facing a white wall to see the difference?From what angle?
I clearly measured 20-30% lumen drop output. I think that, as current increases, the difference gets higher. It is logical up to one point, i believe that the energy from the lost lumens is converted into heat, so we get higher temperatures on the core and a another performance drop. I am waiting for saablaster to confirm this statement.
Dioni
Flashlight Enthusiast
I'm very curious to see the results in the beamshots ! 
Walterk
Enlightened
What I want to see, is how the light comes out from a dedomed led. How it flares away from the die.
Maybe half the beamangle, cut in half by a piece of paper or along the wall ? Something like this but then without optics:
With reflector shows what dedoming the led does for you.
I wonder what I can make from the dedomed. Half the beam indicates how the light and intensity is distributed, so we can find ourselves optics to match the led-characterisitcs.
Thats why I like to see the bare led without optics.
Der Wichtel posted some comparising beamshots in his post Another-dedoming-experiment sometime ago, but they are not that clear.
The picture above is from the most useful open dir archives from Newbie.
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