De-doming xml for projector project. Worth it or not?

Hi,

I converted a projector a few years ago to an xml and have been using it ever since. I can watch online tv etc on a 40" screen with a light on without problems although some very dark scenes in downloaded movies could I think be improved upon. It's running off a 3000mA dx driver on a pc heatsink. I've got a collimator lense and main lense setup.
I know that de-doming reduces lumen output BUT increases throw by reducing the apparent die size. I've also seen that xml's can be de-domed successfully by soaking them for a few hours in petrol.
So my question is would it be worth trying it or do I upgrade it to an xml-2 and maybe try and de-dome that?
All I know is that I need as narrow a beam as I can get and when placed in the projector some of the light doesn't make it directly onto the first piece of glass and bounces straight back so improvements can be made
My tube TV went bang at the weekend so this is getting a lot more use as it was setup in my bedroom.

Ta

Paul.

You still had a tube TV running? Congrats!

Oh, you probably meant a cathode ray tube, not a vacuum tube. But I show my age.

The answer to your question is probably somewhat complex and will be debated some here.

The reason that de-doming increases throw has nothing to do with lumens or die size. That's right. You can halve the lumens, and increase the throw. You can double the die size and increase the throw. At least theoretically. No matter how good your optics, how small your die, or how many lumens you can put out, throw is fundamentally limited by surface brightness.

De-doming increases throw because de-doming increases (apparent) surface brightness. No matter the LED, the optics, the driver, etc. If you can increase brightness you can increase throw.

LED makers put domes on because this increases lumen output. LED makers don't give a d__n about throw. Well, maybe in special cases they do. Luminus and Cree both sell undomed LEDs to prove this.

Now, let's get to your application. What you really want is the highest possible brightness coming out the front of your projector. At this point I could easily be headed into wrongness, but I suspect that means the highest possible brightness at the LED, and that an undomed LED would be better than an equivalent one with a dome.

But how much? A 10% difference is barely detectable in side-by-side comparisons. What might you get by de-doming? 15%? 20%? Probably not more than that. Waiting for others to chime in at this point.

lol, no, my last vacuum tv died when I was about 10, a while ago now. It's annoying as it was a Toshiba tv I was given only about 6 months ago and the picture quality was fantastic.

I didn't think the answer was straightforward hence asking here! Where's Saabluster, Walterk etc when you need them? lol It's a bit of a conundrum which is why I haven't just done it. I've read you can see a 15/20% drop in overall lumen output BUT you can see approaching 100% increase in Lux at the hotspot.

If money wasn't so tight at the mo I'd just buy an xml2 on a Noctigon star, Wavien collar and a 5000mA driver! Pretty sure I would see the differnce then :candle:

No-one got any input or would like to hazard a guess? If I do remove the dome I can take before and after measurements with my lux meter if anyone's interested.

From what I've seen so far, dedoming might reduce the lumen by 10% or so, but this also depends on how its done, with some reporting higher losses, etc. It also comes close to DOUBLING the cd of the light. The effect in flashlights (I have none with projectors used to watch shows) is that the hot spot of the beam appears to be strengthened/concentrated, and the corona/spill reduced proportionally.

When used in an aspherical flashlight system (Closer to a projector scenario), the effect is to turn the beam into a projection of the glowing LED itself...wires and all. As mentioned, the increase in apparent surface brightness produces a corrusponding increase in the light's cd.

As the brightness (Lux) falls off according to the inverse square law: doubling the cd doesn't double the THROW, but it DOES increase it dramatically by doubling the lux on the target at any given range.

So, the image projected can be twice as bright if the LED is dedomed. This is not a perfect ratio, and is based on doubling the apparent surface brightness, as a ballpark end result many see. IE: For example, you might get an 80% or a 120% increase in apparent surface brightness by dedoming.


It takes some practice, so, getting some to practice on might be a good idea before "the one that counts"...and/or one of the practice ones might BE "the one".



As long as you're ordering LED, sure, get the XML2 versions....as their output is higher than the XML version.

TEEJ said:

When used in an aspherical flashlight system (Closer to a projector scenario), the effect is to turn the beam into a projection of the glowing LED itself...wires and all.

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I would have thought that in a projector, you would want to minimise such visual artefacts, not introduce new ones. Sounds like it could ruin the picture completely.

robert.t said:

I would have thought that in a projector, you would want to minimise such visual artefacts, not introduce new ones. Sounds like it could ruin the picture completely.

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The projector is used as a light source to illuminate the screen with a projection of a picture, and, in both instances, it would be lit by an LED. If the LED pattern is TOO focused, it might have a "watermark" type effect on the projected picture, in that the light itself might have a pattern.

So, a simple softening of the LED focus point would probably solve that. For example, some aspheric lights throw a little better when defocused a bit to soften the LED image.

The issues, in addition to the unknown LED watermarking issue (I'm guess it could happen, but, again, have not used one in this context) might be that the size of the apparent source may be calibrated to the size of the projected image, and that a shrinking of the corona, etc, may reduce edge brightness, at least potentially.

The ability to move elements in/out can probably compensate for this, but again, the entire thing IS an experiment afterall.

Paul Baldwin said:

I can watch online tv etc on a 40" screen with a light on without problems

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Honestly, the biggest improvement isn't going to come from dedoming or switching to an XM-L2, it'd come from turning off the light! Or switching it to a lower wattage one.

RoGuE_StreaK said:

Honestly, the biggest improvement isn't going to come from dedoming or switching to an XM-L2, it'd come from turning off the light! Or switching it to a lower wattage one.

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lol, I thought CPF was all about the lumens?! The light in question is only an 11W cfl so not exactly bright. It's just nice to be able to watch the telly and not have to fumble around in the dark, especially if you have guests. Watching studio TV is no problem at all, plenty bright enough, it's just those dark, dark movie scenes I'd like to try and improve upon.

The optics in the projector do a pretty good job of turning the beam into a uniform white light to be honest, de-focusing slightly is a good idea tho if it does become a problem.

I'm tempted to take it outside one of the evenings to get an idea of how tight the current image is.

Paul Baldwin said:

All I know is that I need as narrow a beam as I can get and when placed in the projector some of the light doesn't make it directly onto the first piece of glass and bounces straight back so improvements can be made

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Is this after the LED feeds some sort of optic(s)? Or is this the raw light from the LED? If the former, then heck, give the dedome a shot. If the latter, then you would probably benefit more from a brighter LED or a lens in front of the LED.

I remember your thread from a few years ago, just waiting for a "bad" projector to make its way into my hands ;-)

Paul Baldwin said:

lol, I thought CPF was all about the lumens?!

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Yeah, but you also don't see people doing beam-shots in broad daylight Why fight something when you don't need to? KISS :kiss:

Paul Baldwin said:

The light in question is only an 11W cfl so not exactly bright.

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Isn't that about the equivalent of a 60W incan though? Switch down to an 8W, or 40W equiv, and you should still have plenty of light to see by, but give a good relative increase in screen brightness

bshanahan14rulz said:

Is this after the LED feeds some sort of optic(s)? Or is this the raw light from the LED? If the former, then heck, give the dedome a shot. If the latter, then you would probably benefit more from a brighter LED or a lens in front of the LED.

I remember your thread from a few years ago, just waiting for a "bad" projector to make its way into my hands ;-)

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I just left the projectors standard optics in place. I removed the bulb, carrier and power supply to make space and reduce the risk of a high voltage wake up. The current setup has 2 lenses I have installed infront of the led to focus it as best as I can. Finding a "bad" projector to mess with is well worth it imo. This one was only £20 because a new bulb was £230 list!!!

Rogue. That's a fair point but I think the 11W would be more towards 40W than 60W in the real world so it's not exactly blinding. Fully in agreement with the KISS philosphy tho

TEEJ. What would you say is the best way of ensuring a successful de-dome?

Re dedoming, I've used the petrol method. Soaked 3 XP-E LEDs while I was at work, came home ~10 hrs later and lifted the LEDs out of the petrol. One came out clean, didn't even have to touch the topside of the LED. The other two I carefully picked at the bits of silicone trapped between the bond wires with a clothes needle. This is the part that may or may not be worth the risk. If you malform or break the bondwires, they may not survive as high currents as they could before.

I've got one of my dedomed LEDs in a cheap flashlight host that is easy to replace if this LED craps out. (I used stinky, crappy cheap petrol from a random fill station around here. I'll have to second-guess where I get my fuel, this stuff felt grimy and after a few weeks of further evaporation, turned fairly brownish colored.)

I don't know if this could be considered "Best" method, but it is a method that works. But for all we know, phosphor layer is impregnated in the same silicone encapsulant, and the gas may have a negative effect on the phosphor or *gasp* the actual LED. But then again, it may be just as likely to not have any adverse effects. I ain't no chemist. And I'm too lazy to look up chemical compatibility of InGaN and petroleum distillates. I'll just say that my LED works fine, and I don't have the most delicate touch.

I've heard of another method that takes advantage of optical silicone's low absorption of optical energy. The LED is essentially overheated, and this softens the silicone closest to the LED. The dome is then pryed off. Ceramic substrate is resiliant to picking at, and the silicone that is in contact with the chip has conducted enough heat from the chip to soften enough to break instead of pulling up the phosphor. I've not tried this method, but it sounds scary. I do like that there isn't a solvent involved, though, but don't know if there are any permanent effects from running the LED at whatever temp is necessary to soften the silicone.

You might consider practice on the XM-L, and if easy as you thought, get an XM-L2 and upgrade your projector. XM-L2 has 2 bond wires for the LED chip instead of three, and is flip-chip design, so you don't see the current spreaders on top of the chip, meaning instead of distracting dark lines, you may see less bright spots, if LED is focused perfectly sharp.

I've tried both methods. The heat and pry, and the gasoline.
The gasoline is much easier, and definitely less scary. Overnight in a bath of gas, and even of the dome is still even there at all, what's left will slide off in the bath.
I put a series of cuts in the dome so the gas soaks in faster, and most of the time I come back, and the dome is completely gone.

The heat method always leaves little chunks of dome around the bond wires, and around the chip, so after doing a couple, I've turned to gas every time.
And the pry method actually left a little dome left somehow. To clean them up, I dropped the pry off leds in gas. After a few minutes, a very thin layer of dome that was left came off in the gas bath. So it's not only easier, less risky, it's more thorough.

As above, I did mine in petrol with no issues whatsoever; here's the quote from here:

Just did my first de-dome (XM-L), with 100% success; scored the dome a few times with a blade, then soaked in petrol (91 RON "standard unleaded") for 21hrs. Was waiting to see if the dome just floated off, but it didn't. The slightest of touches with a plastic toothpick and it popped right off, no goo left except a tiny bit under the bond wires. Little bath in some isopropyl (very hard to find in Aus due to drug-lab restrictions etc., used Isocol from the chemist) and she's all good. Surprisingly when I picked up the dome it completely disintegrated into dust.
Seems warmer, and definitely a smaller, more intense die image when behind a lens; seems about 3/4 off it's previous size.

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And the beam comparison

Have you considered using an MT-G2 instead? It's 2.5x brighter than XM-L2 and has a lovely neutral tint. Seems like it would be perfect for this application.

flashflood said:

Have you considered using an MT-G2 instead? It's 2.5x brighter than XM-L2 and has a lovely neutral tint. Seems like it would be perfect for this application.

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I don't think the MT-G2 would offer much advantage sorry. I know it kicks out the lumens but the size of the die doesn't help in this application. From my recent bit of googling to see what results others have got with this sort of project it seems most go for 100W leds! My results seem comparable from what I can tell, it uses a tenth of the power and I don't have to cope with all that heat. My setup is actually way quieter than standard. When one of the fans died due to old age I did away with it completely. It now only has one very small pc fan just to trick the projector into not shutting down due to the bulb protection feature. Every time I turn it on nowadays it tells me to replace the lamp!

Rogue, those photos are great ta, a picture paints... and all that

Cheers for the de-doming info too chaps. Seems the petrol technique is pretty much a no-brainer, just the sort of route I need lol.

Looks like I may need to make the install more permanent, finish things off a lot better and ceiling mount it. Now I've tweeked it a bit more and realised it's really quite liveable with when plugged into the TV dodgy box I have I don't think I'll be replacing the telly. It's saving me a 100W too which is a nice little bonus.

Sounds like most of you have had good success with gasoline (petrol). I have not. I have ruined several quality LED's using the gasoline method and will never again use this method. Instead there is a much better and well documented method which will produce excellent results. http://electroiq.com/blog/2007/08/solutions-and-solvents-for-removing-silicone-a-practical-guide/

I use the heat and pry method. I have de-domed around 300 leds and only a couple of fails have occurred. I once broke both bond wires on an XP-G2 and I know that you will not believe this, but I just soldered them back together. Yeah it works. The other fails were when I didn't know about heating and didn't do it. This leads to a little bit of the top layer coming off and projecting blue light. This was more of an issue with XM-L and other leds from that generation this new generation is a little more robust. The leads are better as well. The major thing that no one has mentioned is the color shift that you will experience. I would use a 5000k led prior to the de-dome in order to get the correct temperature after the de-dome. The noctigon is the way to go, I have quite a few and they do the trick of keeping the led cool and the heat-sink hot. You should also use some high quality thermal paste and ensure that the oxide layer is removed from both surfaces prior to mounting. What type of heat sink is the star mounted to? I assume aluminum. This sounds like a neat little project, you should look at the variable output DC-DC converters that are available. They work great and allow you to hook up a current meter in line and determine exactly where you want to set your current. This allows for a better determination of both color renditions due to over-drive and heat dissipation as you can also test the heatsink temperature while doing this to see how you stand. The XM-L2 is a much better led than the XM-L in more than just efficiency, you should definitely get one. I don't know the answer to which would be better for your application but as far as I am concerned it always helps. What people don't typically realize is that source lumens don't mean anything it is the light gather and lens clarity/focus that leads to the ultimate amount of light that you will use. If this is an aspheric set up you can look into other leds, but I do love the XM-L2s. Where is your power coming from? Are you getting it from internal DC power like 12V? If so you should look into a direct move to the MK-R led because it is ran from 12V or around there and you would get more efficiency from your driver. You would also get more light output per watt.