The wider angle lens does have shorter focal length (ie greater optical power), but “wider” here doesn’t mean the same “wider” as beam collimation. In the camera case, the wider refers to less movement on the film/sensor for same angular diff in the scene (therefore more stuff in the photo), but in the latter case wider is the spread of a light source at the film. In any case, you can compare the cree published output curve against a cos function to see the diff.
The contention here isn’t about what light is approx going where, but more nuanced optics.
The cree data is for an led on a flat surface. Once you put that led at the back of a lens, the viewing angle data goes out the window.
I read the posts from the first few pages, and the dialog was most certainly about what light is approx going where. You mentioned that the dome focuses the light, rather than disperses it.
And once again, the experience of posters on this board seems to show that the dome in fact does disperse the light, since the removal of it concentrates the light to a fairly extreme level in comparison to when the dome is still on.
No, the data is with lens. This is why it’s different for xr-e vs xp-e. Again, as noted it should be a sin curve given reasonably diffuse surface sans lens.
you seem like the people who used to say that the way a dragsters tires appear to be expanding at the starting line, was nothing more than an optical illusion.
then they studied it with high speed cameras and found out that the tires were in fact expanding.
well we have our camera proof, the dome does prevent some of the focused energy, and removing the dome eliminates some of the spread.
and no matter how hard you wish, you’re not going to make that go away.
Have you seen this thread here where some aspects of this subject is discussed too? Very interesting experiment in there by djozz in corroboration with Dr. Jones... :-)
That shows what makes the spot and what makes the spill.
Dedome definitely spills the light out more evenly sideways and all.
And that is exactly why we see more focused beam, because the event simply allows the reflector to work and do its job. This is very obvious in dedoming, I have 2100, P60 and T13 dedomed and the beams pretty much copies the reflector now. The 2100 beam even copies the uneven rings at the reflector base heheh...
What LED.A said was true about the result - but what camera captured as better focused beam was the after adding reflector into account.
I recently tried dedoming an XM-L and putting it into my modded Sipik SK58 budget zoomie.
I used the method of heating the XM-L done with a soldering iron then using a long-nosed pliers to slide the dome off. First attempt I heated the dome too much and it broke into chunks. Second attempt worked better. Not perfect, but not bad. Dome pulled away in 1 piece. A tiny bit of the phosphor pulled away from 1 corner, but most of the phosphor layer was intact.
I was experimenting with U2 1A tint emitters that I’d purchased from Illumination supply. I was hoping that the cool white would shift close to a 5,000k neutral tint. It didn’t. When I looked at the focused image of the emitter as projected through the aspheric lens, the tint was very slightly yellow, but still definitely cool white. Not as white as with the dome on, but definitely not neutral.
In flood mode, the reduction in lumens was quite noticeable. I use a small reflector inside my zoomie. In flood mode with a domed XM-L this eliminates all rings that aspherics tend to have, and adds a broad hotspot covering most of the beam. With the dedomed XM-L, the hotspot was still evident and appeared to be just as bright, but was smaller and more centralized to the center of the beam The side spill of the beam was noticeably dimmer. In a ceiling bounce test, this light produced noticeably less lumens than a comparable light with intact dome.
In spot mode, the dedomed emitter had significantly enhanced throw. Much better than the stock XM-L. The die image of the dedomed emitter was about the size of an XP-G, but much brighter. (I am using a 2.8 amp driver).
The results were about as expected. Dedomed, the emitter spills more light out to the side. But at the same time all the light is coming from a much smaller point source because the dome isn’t magnifying the die image. The result is more throw regardless of whether the light uses a reflector or an aspheric lens. However, without the dome, more light is lost to internal refraction inside the die crystal so overall lumens decrease.
I have 2 more U2 stars to practice with. Not sure if I want to try dedoming one of them to see if I can do a better job on the dedome. Or if I should just leave in a domed U2 emitter, or go back to my domed T6 neutral emitter.
[quote=LED A. Stray]
you seem like the people who used to say that the way a dragsters tires appear to be expanding at the starting line, was nothing more than an optical illusion.
then they studied it with high speed cameras and found out that the tires were in fact expanding.[/QUOTE]
Drag tires do no expand but rather deform radially on starts. Any simple camera with reasonably fast shutter can illustrate this.
No, there’s zero “camera” evidence that the dome does any such thing. You can however take a shot with a bare xml sample to make your case. You’ll likely find the cree data to be correct.
If this seems so simple, perhaps you can explain how exactly the engineers at cree are off by a factor of about two given the dome very significantly increases the output flux of the led.
Popular Mechanics called, they said you should probably leave this topic alone.
“With increasing vehicle speed, the tires expand to a final diameter of 44 inches”
That was literally the FIRST hit on google when I typed in “top fuel dragster rear tires expanding”.
Feel free to peruse google further to find some seminal work that shares your views.
Those are before and after pics that are posted earlier in this thread for a light that was de-domed.
I’ll let you figure out which one was the before, and which one was after.
I’m out.
Enjoy the last words in this conversation.
Popular Mechanics called, they said you should probably leave this topic alone.
“With increasing vehicle speed, the tires expand to a final diameter of 44 inches”
That was literally the FIRST hit on google when I typed in “top fuel dragster rear tires expanding”.
Feel free to peruse google further to find some seminal work that shares your views.
You are so ignorant. This whole time you didn’t even know how a flashlight worked. The bottom picture with the more yellow tint is dedomed. Why is there a brighter hotspot and less spill? Because there is no dome to concentrate the light forward and create the spill. Instead, MORE light hits the reflector which forms the hotspot.
tldr; the light which hits the reflector forms the hotspot, anything that doesn’t forms the spill.
Now reflect on how stupid you sound. Learn your stuff before you try to argue. What a waste of my time.
The reason why dedoming “works” is IMO not trivial. At the distance that the cree lens is placed at, it doesn’t even focus all that much. It seems the primary purpose of the lens is to provide a medium with higher index of refraction to interface with the dense material (sapphire) above the semi material. My hypothesis is that at the off-axis angles that actually hit the reflector, the varying degree of magnification across the die due to the lens (you can see this by looking at an xml from the sides) tends to also make the focal point of the virtual image of the die less consistent to the reflector (ie whereas a point on a flat die will always appear at the same spot, the same point behind the lens tends to vary with the angle to the axis). I think a ray tracing simulation of some sort would be necessary to verify this since light is really a vector instead of just scalar value.
If all the dome did was focus the light so more of it went forward instead of to the sides then the end result of de-doming should be more throw with a reflector, but LESS throw with an aspheric lens. But this is not what happens. Instead, de-doming significantly increases throw with both reflectors AND aspheric lenses.
This is what I think is happening:
The dome acts as a magnifying glass that increases the effective area of the die, but reduces its effective surface brightness. Since the light isn’t coming from such a focused point source it is harder to focus and gives less throw in both aspherics and reflectors. When you de-dome the emitter, the light is coming from a more concentrated point source. Effective surface brightness increases and you get more throw regardless of what type of focusing system your light uses.
However, without the dome in place, more light is lost to internal refraction inside the LED crystal. This leads to an overall reduction in lumens.
@agenthex: What do you think would happen if you use dedomed XM-L with TIR optics?
I might be wrong, but didn’t see anyone has tryed out what happens with TIR.
Yup, magic. And no, I don’t believe frequency is conserved(this is not monochromatic light) so there are multiple frequencies involved which can be refracted/reflected differently. Refraction occurs whenever there is a change in medium density(dome to air). Reflection back to the emitter (and reabsorbtion/loss of output) is maximized at 90(flat cut of dome parallel to emissive surface). Dome shape MAY be a design feature to minimize refraction and maximize light transmition through the dome/air interface. Some of the higher frequency light may be reflected back and reabsorbed by the emitter. I have not yet been through this entire thread yet as this topic only recently became of interest to me so I applogize if this response is dated.
+1. This is precisely what has me interested in this thread. Could this be a way to use a cool white emitter with a tir optic to obtain a more focused neutral/warm beam.
Edit - response to Ledoman
People should realize that the reflector does not only reflects the light but it also curves the light. To converge the light into a single hotspot. That why the light from the reflector creates the throw like Slewflash said. The light from the die itself is still diffuse and that makes the spill.
TIR is designed using sophisticated ray tracing for a specific output profile, and I think much more sensitive to this given the way they work (ie more internal reflections). Without trying it all I could say is that it would probably be more different than originally intended compared to the simpler optics.
Your are correct in the bolded text above. The vast majority of the IR is at the interface between the emitter top layer and dome (and by dome I’m including the phosphorus gel), before the phophorus layer unless that gel itself has crazy optical density. The way the dome is shaped, IR at the outer surface should be much less (since the surface is perpendicular to the light. IOW, more is lost before being made into the spectrum.
Almost all the light lost to IR would be in the higher freq part of spectrum, ie blues.
In summary, the implication of this is quite interesting since it demonstrates that far more light is lost at the first interface w/o dome, because the dome decreases the loss at the first interface while increasing it at the second (given the second doesn’t exist without the dome). In fact, the disparity is so large that even though the outer face of the dome should be making the light warmer (by removing some of the higher spectrum), it’s dwarfed by the higher spectrum content lost without it.
