# why would any one dedome LEDs ?



## gamezawy (Aug 26, 2013)

hi all

i saw some ppl dedome there leds so why ? and what is its relation with better throwing if i am correct ?


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## Chodes (Aug 26, 2013)

Mods will probably move this to LED forum, definitely belongs there.
Saying "do a search" is not normally regarded as a great response on forums but for this topic you should search.
I did that a few days ago.


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## Slewflash (Aug 26, 2013)

On my phone so I'll give a quick reply. 
It decreases apparent size of die which increases surface brightness. It also decreases angle that light is emitted by 13°. 
In short, it increases throw (can double it or more depending on reflector) , makes the tint warmer and loses a small amount of lumens.


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## Wiggle (Aug 26, 2013)

Slewflash said:


> On my phone so I'll give a quick reply.
> It decreases apparent size of die which increases surface brightness. It also decreases angle that light is emitted by 13°.
> In short, it increases throw (can double it or more depending on reflector) , makes the tint warmer and loses a small amount of lumens.



Yep, this is right. You basically make a trade where you lose some lumens but potentially gain a significant amount of throw.


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## TEEJ (Aug 26, 2013)

As your question is actually about WHY people do it:


Its worth it if the light you have is bright enough, and you otherwise like it, but, you wish it could hit more distant targets.

Otherwise, it means you could have just bought a light that could shine that far to begin with, etc.....or, the lights with extra range were out of your price range, so you "souped up" the econolight to make it perform as needed, but w/in budget.

It can ALSO be done to simply maximize the throw of an already alpha-dog light, to make it even more throwy, etc.


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## gamezawy (Sep 24, 2013)

Slewflash said:


> On my phone so I'll give a quick reply.
> It decreases apparent size of die which increases surface brightness. It also decreases angle that light is emitted by 13°.
> In short, it increases throw (can double it or more depending on reflector) , makes the tint warmer and loses a small amount of lumens.



so you mean that if my led angel is 125 and by dedoming it . it will be 125-13 = 112 degree ?


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## AnAppleSnail (Sep 24, 2013)

gamezawy said:


> so you mean that if my led angel is 125 and by dedoming it . it will be 125-13 = 112 degree ?



Roughly speaking. It means a bit less light gets out of the LED, but the LED will pack more throw out of your reflector or aspheric. However, it IS possible to mess up a de-doming process. This lowers your lumen count so much that you don't gain much throw at all.


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## TEEJ (Sep 24, 2013)

If you do a good job, and don't remove phosphor, you lose a little OTF lumen output because the dome was helping the reflector get the light distributed better, and w/o the dome, what used to be some spill and some corona is now shifted to the hot spot...so there's less spill and corona, but more hot spot lumens being sent OTF.

Some of the lumens are lost in that transition though, but the over all impact is potentially doubling the cd of the light (I'd say doubling the cd instead of doubling the throw...as some might think doubling the throw is doubling the distance in meters, etc...which it is not).

So if you have a light you like, but wish it could throw harder, you might be able to bump it from a 20k cd to a 40k cd or 100k cd to 200k cd, output by dedoming. (That might be +/- 20% or so)

IF you are doing it to get more range, the lumens that are lost are not going to matter much, because the spill for example was not helping you see anything far away anyway....ONLY the hot spot reaches distant targets.


Now, if you do damage the phosphor on a bad de-doming attempt, sure, you throw the LED in the trash and start with a new one.


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## degarb (Sep 27, 2013)

TEEJ said:


> If you do a good job, and don't remove phosphor,




As I posted before, I botched two xmls, carefully slicing off tip then progressively more of the dome. At even just removing the tip of the dome, things got colder and dimmer. I think rememer I testing current, so likely no weird forward voltage shift going on.

No luck with Exacto knives, I wonder if you could dedome one by buring off the dome with the soldering iron tip? Has anyone tried this? 

I am still tempted to buy another cheap t6 dropin and butcher it. Does this make me some kind of a serial killer?


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## TEEJ (Sep 27, 2013)

degarb said:


> As I posted before, I botched two xmls, carefully slicing off tip then progressively more of the dome. At even just removing the tip of the dome, things got colder and dimmer. I think rememer I testing current, so likely no weird forward voltage shift going on.
> 
> No luck with Exacto knives, I wonder if you could dedome one by buring off the dome with the soldering iron tip? Has anyone tried this?
> 
> I am still tempted to buy another cheap t6 dropin and butcher it. Does this make me some kind of a serial killer?



Yes...you are the Cree Butcher.

Don't slice it, just pry it off....from the bottom....get under it and flip it off.



Some people find soaking it in solvent works well too....seems messier to me, but hey, everyone has their own techniques. I see people try a few ways, and essentially - whatever WORKED, is what they keep doing.

Even the people who are de-doming a dozen a day (Vinh, etc...) keep spares though, as they assume even they'll have a few ooops here and there....so there's always a chance at least of screwing up....you just got YOUR screw ups out of the way early.



Its cheaper to just get the LED instead of a drop in...so if you want to practice, its a few bucks a pop.


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## RoGuE_StreaK (Sep 28, 2013)

I just dumped mine in petrol (91 octane "standard" unleaded) for 21hrs, and it popped right off with the slightest touch, with no residue at all except a little around the bond wires (where you kinda want it). Sliced the dome a few times with a blade before it's dunking, supposedly that speeds things up. Dome crumpled into dust when I went to examine it.




As for the "why", here's a beam comparison (rough, overexposed); SK68 with domed XP-E, SK98 with original domed XM-L, SK98 de-domed. ie., last two compare the exact same torch with it's original dome vs after a de-dome.


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## degarb (Sep 29, 2013)

RoGuE_StreaK said:


> As for the "why", here's a beam comparison (rough, overexposed); SK68 with domed XP-E, SK98 with original domed XM-L, SK98 de-domed. ie., last two compare the exact same torch with it's original dome vs after a de-dome.




Based on the above picture, it looks to me that the domed beam is brighter and bigger. Like my botched jobs, except warmer.


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## TEEJ (Sep 29, 2013)

degarb said:


> Based on the above picture, it looks to me that the domed beam is brighter and bigger. Like my botched jobs, except warmer.


Its typically impossible to judge brightness based on wall shots. If the beam is smaller...that's easy enough to tell, and normal for dedomed led. If smaller, it means the lumens are all more concentrated....hence higher lux.


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## RoGuE_StreaK (Sep 29, 2013)

Yeah bad phone photo (I didn't pre-adjust the exposure), from a purely subjective viewpoint it (de-domed) appeared to me to be about the same brightness, but definitely more concentrated, maybe 2/3 - 3/4 the size at the same distance, which equates to a lot more throw. I didn't take any outdoor ranged comparison shots, but it definitely throws better.
Also warmer, it's actually turned out quite pleasant. Flood is still massive, didn't notice any real difference there, which is a good thing. Not bad for a $12 torch


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## The_Driver (Sep 30, 2013)

The correct explanation of de-doming form Dr.Jones can be found here. He also mentions common misconceptions of how it works. Many people have wrong ideas about it. 

In the end the following things will happen:
- the lux values of a flashlight will almost double
- around 10% less lumens (for Cree LEDs)
- the tint will become warmer, maybe around 1500K less than before
- the hotspot will get smaller


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## TEEJ (Sep 30, 2013)

The_Driver said:


> The correct explanation of de-doming form Dr.Jones can be found here. He also mentions common misconceptions of how it works. Many people have wrong ideas about it.
> 
> In the end the following things will happen:
> - the lux values of a flashlight will almost double
> ...



This sounds exactly like my impression as well.

I'll add that the spill and corona shrink as well depending on the type of light...with the impression being that the hot spot was augmented by output that was previously in the spill and corona...so as they are reduced, more lux is available for the hot spot.


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## The_Driver (Sep 30, 2013)

TEEJ said:


> This sounds exactly like my impression as well.
> 
> I'll add that the spill and corona shrink as well depending on the type of light...with the impression being that the hot spot was augmented by output that was previously in the spill and corona...so as they are reduced, more lux is available for the hot spot.



The hotspot becomes smaller because the apparent size of the die decreases (the dome magnifies the die). 
The lux values only go up because of one thing: the led is more intense than before => its luminance is higher. 
The led becomes more intense because light reflected off the surface of the die back into the led can be converted to white light again and emitted at a different angle by the phosphor. Removing the dome means that more light is reflected back and re-used (=> total internal reflection). 
This has to do with the refractive index of the phosphor and of the dome. Please read the explanation I linked to in my earlier post.


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## TEEJ (Sep 30, 2013)

The_Driver said:


> The hotspot becomes smaller because the apparent size of the die decreases (the dome magnifies the die).
> The lux values only go up because of one thing: the led is more intense than before => its luminance is higher.
> The led becomes more intense because light reflected off the surface of the die back into the led can be converted to white light again and emitted at a different angle by the phosphor. Removing the dome means that more light is reflected back and re-used (=> total internal reflection).
> This has to do with the refractive index of the phosphor and of the dome. Please read the explanation I linked to in my earlier post.



No question...I meant that the impression, as in, what you see when looking at the beams, in comparison...is that some of the the light that was in the corona and the spill was transferred to the hot spot, not that it was LITERALLY transferred.


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## The_Driver (Sep 30, 2013)

TEEJ said:


> No question...I meant that the impression, as in, what you see when looking at the beams, in comparison...is that some of the the light that was in the corona and the spill was transferred to the hot spot, not that it was LITERALLY transferred.



Ok, sorry. I misunderstood you 

Another effect in that sense: it makes a flashlight seem more powerful


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## TEEJ (Sep 30, 2013)

The_Driver said:


> Ok, sorry. I misunderstood you
> 
> Another effect in that sense: it makes a flashlight seem more powerful



LOL


Its always like that - the more glare it makes, the brighter its perceived as...almost w/o fail.


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## bshanahan14rulz (Sep 30, 2013)

Often, the "corona" of TIR based lights is simply an image of the die. If the die's apparent size from the lens' point of view gets smaller, then the image that the lens projects will be smaller too. 

On reflectored lights, not really sure where the "corona" comes from. Is just the texture of the reflector?


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## The_Driver (Sep 30, 2013)

bshanahan14rulz said:


> Often, the "corona" of TIR based lights is simply an image of the die. If the die's apparent size from the lens' point of view gets smaller, then the image that the lens projects will be smaller too.
> 
> On reflectored lights, not really sure where the "corona" comes from. Is just the texture of the reflector?



The square part of the beam is caused by the center part of the tir lenses. It is usually formed in (apsheric) lens like shape which projects an image of the led die. The round part of the spot is caused by the much bigger, outer part of the tir lenses. If you put a round piece of diffusion foil in the middle of the tir lens (on top or on the bottom) you can get rid of the square image.


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