Acrylic ball lens for tight even beam

A simple mod I did using a Techass PR2 shows the effect of an acryllic ball used as a lens:



The PR2 unaltered beam is shown below:


A 1" clear acrylic ball is held up to the light with the distance to paper being the same:


A similar but less dramatic effect is possible holding the ball up to an Arc AAA. By adjusting the distance of the ball from from the LED a very small bright beam can be obtained.

It may be for a single LED light to function as both a wide angle "candle" as well as a narrow bright spot a focusing lens applied to a wide angle LED could perform better than a narrow beam LED with a difussing lens. Certainly with the ball mounted in a sliding tube, an adjustable beam would be available.

The PR2 appears to have a shortened head. This seems to be necessary for the ball to get close enough to the die and to allow for an adjustable focus of the light beam. It would be very interesting IMHO if one of you with good light measuring equipment could experiment with this. The acrylic balls are pretty cheap at places like Tap Plastics and I assume that the LED's can be shaved and re-polished.

The beam resulting from the ball lens is very even in brightness to the naked eye.

Junior science project 1B completed....

Since this was such a popular post with wide spread comments I decided to add additional photos:


Above and below, a Luxeon emitter is placed against the 1" acrylic ball.



And below, an Arc SLS on the left and ball lens on the right.



(since I don't have brass ones, I play with my plastic ones )

Hey don,
Cool pics! Thanks for sharing them! BTW, I think I know you!

Careful there, Don #2. Don #1 is a bit touchy about his mods...

I just have one question: Does the thing bounce when you drop it face-first?

Excellent rebound, especially on concrete!

Why thank you for asking

Counting the already-manufactured-in optics of the original LED, in effect isn't this a light beam passed through two lenses?

No point being made here, just an observation...

Ooh ooh! I was going to post to this on the weekend, but got distracted.

Anyway, while out shopping I found some little 15mm acrylic balls, and remembering Don's post, thought I'd try it. So at home I found some plastic tubing with about a 12mm inner diameter. I jammed one of the balls into a small bit of tubing, and then stuck that on the end of a white Arc AAA, with the ball sitting right up against the LED.

Bingo! A nice even beam circle similar to what you get with the PT Impact.

It sits on the end of an Arc AAA quite well - there is just enough tubing to hold it onto the bezel, but leaving enough space to turn it on and off.

I took a couple of photos but don't have them here at work. I'll post them tonight when I get home.

Graham

Mr. Bulk, I think you are correct. Or in the terms of say camera types you could call it a lens of two elements. The collimator used on the LS might also be considered a lens so a LS with optics I believe could also loosely be considered a lens of two elements.

I would however like to point out that my balls bounce much better than the collimater ( I have intentionally spelled collumator three different ways and probably still didn't get it right)

I was playing around with an Arc LE and some different lenses a while back. The best combination I came up with was holding a globe-shaped map magnifier in front of the Arc LE.

I was easily able to light up a target backstop in the back yard (after dark, of course) which is about 55 yards away from the back of the house. This was also while shining the light through some heavy glass sliding doors (I was inside the house). The amount of light didn't have near the same authority as say a Surefire E2 would but, nonetheless, it was still quite impressive.

On the negative side, the map magnifier is about 4" diameter, and you had to hold it about 4" away from the front of the Arc LE to get the best beam. The beam could almost be described as a huge laser beam, with no light spillage outside of the beam at all.

I have some small, clear marbles but to get the tightest beam, they still have to be held slightly in front of the Arc. Does anyone know what might happen if maybe a third of the marble was ground off and polished. Would that make it focus the light better while being held (hopefully attached) to the front of an Arc?

I don't think that any lense small enough to attach to an Arc LE could possibly duplicate the power that you can get from a much larger lense but, if we put our heads together, maybe we might come up with something practical.

-bucken-

Bucken,

I think that you will find that a hemisphere, 1/2 of the ball will will also work but give a sliightly different beam angle (wider). The farther you are from the LED, the larger the diameter of the lens needs to be to catch all of the light from the LED and redirect it. With the chopped head of the Techass PR2, the ball lense seems to be able to get on the other side of the focal point of the inherent lens in the LED itself. This allows for the external lense to be adjusted in relative position and vary the beam angle. What impressed me the most is the evenness of light distribution with in the circular beam pattern as well as the abrupt cut off from light to no light. ANyone with a luxeon star w/o optics can see that an external lens can be brought close to the LED and a very impressive beam pattern can be obtained. These plastic houses also sell hemispheres of acrylic to be used as legs on acrylic boxes.
The curvature of the surface of the lense and refractive index of the material dictate how much the light is bent as I recall from HS physics (many years ago). With this simple ball, much of its mass is unnecessary for the same beam result. A M&M shaped lens where you would take the two curved surfaces and bring them closer together would also work. I suspect that a freznel maginfying glass could also provide an interesting beam.

With an incandesent light source that is sending out light at all angles, A parabolic reflector is required with the light source at the focal point to catch all light and re direct it in a beam. The LED's already have the light directed in a more defined beam and therefore I think a lens can effectively be used for further re-direction.

Note: the above information is speculation based on impaired reasoning and understanding.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by McGizmo:

Note: the above information is speculation based on impaired reasoning and understanding.

<HR></BLOCKQUOTE>
Damn. It sure was a lot of words though. I was *really* impressed right up until the discaimer.

Leo,
I don't have any of the hemi-spheres but I have chucked a ball in the lathe and turned a flat and shoulder in a ball to get it to sit into one of my Tri-clusters. It worked fine but since there are 3 LED, I got three distinct round dots of light on the wall. Too narow of a beam for the application. You can use these lenses to see the ugly die pattern in the LED if you set the focus wrong. I am confident that a flat surface against the LED will allow for more ligght transfer through the lens. If the angle of incidence is too great ( Angle of light hitting the lens surface) the light will bounce off the lense instead of going through it. I suspect that if the ball were drilled to mate to the LE as the collimater does, the maximum amount of light would go through the lens.

As I've suggested above, these ideas should be tested with good light reading equipment to see what loss in light occurs. As we have discussed off forum, Design around the emitter instead of a star allows for more options in the design of the mating surface and configuration of the "host" structure of the emitter. The existing collimator or other type of lens could be added to the emitter as desired.

I really like the idea of a glass lens as it would serve to filter out damaging UV from the ambient as well as provide a long lasting, non yellowing lens for the light. If we are going to be messing with this stuff, why not mess with the directivity of the photons as well as the number produced. ( yes, I'm refering to the particles D)

- Don

I really need some acrylic balls now...

Don, any chance you've got beam pics using the acrylic hemispheres you were talking about earlier? Another thing to consider is the transmission losses thru the acrylic itself. Even the standard PMMA NX-05 optics that come with the LS/O doesn't have that great a performance. How would a large mass of acrylic like that fare efficiency wise?

FWIW... I have learned that a small fresnel lense works nearly as well as the much larger globe-shaped map magnifier! The fresnel lense is thinner than a credit card and about the same size (in fact, I carry it in my wallet where I almost forgot about it).

On the downside, however, I have to hold it about 8 inches away in front of the Arc LE to get the most powerful beam. Hmmm... That's also about the same distance that I have to hold it away from a page of small print in order to read it the best. I think I remember seeing some fresnel lenses somewhere that just lays flat on a map and everything looks bigger without having to hold it away from the page. Wonder if something like that might be better? Does anyone have a different fresnel lense they could try?

-bucken-

Just a little history lesson, thats because the fresnel lens was invented to replace roundish lenses. The round lenses (globe I guess, round implies flat I guess, mathmatically anyway) were large, heavy, and broke easily, that is the reason for all the consentric circles in the fresnel lenses...

Since we're on the subject of lenses I'll talk for a moment about stage lighting, maybe if we all put our heads together (ouch!) we'll be able to get something practical out of it.

There are 3 main types of lighting instruments, PAR cans, Fresnels, and Elipsoidal Reflector Spots, hereforto known as ERC.

Par cans are just that, a can that you stick a large parabolic bulb in, you can use the same bulbs as you use in outdoor flood lights. No focus, most LED lites seem to be running on this concept.

Next is the Fresnel, it's a little more advanced, they have a frenel lens in front of the bulb (hence the name...) and then there is a large cleap bulb inside the lamp on a mount that can be moved towards the back of the lamp or towards the front, there is also a parabolic reflector in the back of the light housing...moving the lamp away from the lens causes more of a spot, moving it closer to the lens gives it more of a flood.


The most advanced type (And therefore the most expensive...) is the ERS. This uses a huge reflector and lots of lenses to give you a highly focused beam of light. You can make the spot larger or smaller but it stays a beam. You can use shutters to cut out the beam on the edges among other things...these are an electricians best friend.


Some sort of fresnel lens would make a great flashlight lens, you can get a highly focused beam, or a nice flood. You would need a way to move either the LED or the lens, fortunatly many lights (Think Mini-Mag and I'm not even bashing it) have a mechanism like this already. How about a tiny precision engineered fresnel lens made out of Lexan? That would be sweet!

Some related thoughts/ comments. It has been mentioned in another hot running thread that dimpled reflectors are more effective than highly polished reflectors. They are more effective in bluring the imperfections and inconsistancies in the light source.

Mag's reflectors deliver a very efficient level of their light to target but mirror the imperfection of the light source as well. Hence, BU beam that is criticized relentlessly here in CPF.

I think the dimpled reflector is akin to the nylon over the lens of a camera to soften the picture. In fact, has anyone tried shooting a flashlight through a fine mesh, like some nylons? "Pantyhose beam shaper warms colors to fall fashion"

Any way, whether the light is redirected via reflection or refraction, loss will occur to the extent that the material used isn't perfect. From what little I can gather with only visual evaluation of photon re-direction, I think shaving and re-polishing the head of an LED coupled with an optics qualiity glass lens has the best chance of yielding an evenly defined and dispersed beam of light from a single LED.

With the LS, I think a bare emitter coupled to a glass lense could yield a directed beam of light similar in intensity to the collimator. For mods and durability, A glass lens might be easier to inccoporate into the flashlight head and would not be as prone to scratches and wouldn't yellow over time.

I have a fresnel magnifying glass as well but the magnifying glasses of either format are not powerful enough to effectively
redirect the light in the fashion we are after. I've been meaning to test a jewelers loop but keep forgetting to. There are some inexpensive glass loops of high power magnification that might provide a viable lens.

I've got it...a glass lens of some sort (Perhaps fresnel but whatever) or maybe Lexon, since it's nearly indestructable but I don't know how well a lens it would make, anyway..in a housing like on flashlights where you could turn something (In this case the head) and have the lens move closer or further away from the bulb. The lens would be set back enough that it would be more or less protected from most scratches and such.

Another way to describe it is a combination of binoculars and a telephoto lens...get it now? If not go expose the film in your telephoto camera and watch the lens go out and in from the inside of the camera...


**EDIT**

Ok tried it witn some 20x-125x Bincoculars and it kinda worked...I had to use my non-led Noric with the headcap still on it which affected performance a little I'm sure

I tried a few different configurations and the one that finally worked was shining the light backwards through the binoculars which made the light cast a very nice very even "beam" of light on the wall, when I moved the zoom thing the light got more spread out...wasn't very bright but that could've been for many reasons.

In conjunction with some experimenting on Luxeon Emitters, I took some shots and some light readings of a LE with the collimator as well as a 1" ball lens. You can see some info and images HERE

To determine relative efficiencies of various lenses and reflectors would require a system like Craig has as well as a more controlled light positioning mechanisim.

The more I have played with the Luxeon LED's the more I can appreciate the challange faced by anyone making drivers for them. Inconsistancies in color and and working volt/current relationships from one LED to the next would make it tough, IMHO, to predict the results of a random selected Luxeon coupled with a designed circuit. I am in way over my head on the electronics side but it looks like you have to have a circuit that will give you a specified current while the voltage may vary.

I have seen it stated here that " Your mileage may vary"....... It might be more appropriate to state: "Your illumination may vary"....

I forgot to mention here on the post that the ball lens provided a 50% brighter reading than the standard Luxeon collimator; 4890 Fc VS 3090 Fc at beam center. This is primarily due to the tighter beam. I tried a glass jewelers loop and it also tightens and cleans the beam; not as much as the collimator or ball.

Ok, I had said I would post the pics of what I did with the acrylic ball and an Arc AAA, here they are:


Just a 15mm acrylic ball attached to the end with some narrower plastic tubing


Slightly blurred close up


The resulting beam, at a distance of about 1 foot or so - the beam is actually quite visible at a distance, has a better 'toss' than an unadorned LED..
I kind of like it..

Graham