# Binocular Indirect Ophthalmoscope



## drneale (Nov 10, 2008)

Hi. I'm an eye doctor at the University of Virginia interested in developing my own equipment. In particular, I use a device called a binocular indirect ophthalmoscope. It sounds complicated, but is simply a glorified flashlight worn on the head. The problem is that the commercially available products are large, cumbersome, and cost 3 to 5 thousand dollars. There is obviously a lot of miniaturization that has occurred lately that could be capitalized upon.

I have made a prototype that weighs only a few ounces using a xenon bulb assembly from Princeton Tec Rage (only cost $3) and two CR123 batteries. 

Its bright. very bright. However, the beam is too diffuse. I need it to focus to about a four inch spot at a distance of about half a meter. I have tried several converging lenses, but can't get it to look right. 

Also, I'm sure that the light and power supply I chose could be improved upon. With the encyclopedic knowledge the users of this site seem to possess, I hope I can improve my design. 

A couple stipulations: 
1. The light source has to be similar in color to incandescent. I am using a xenon source and it is just right. LED just won't work.
2. I would prefer a rechargeable lithium ion battery. This is something I may use for up to two hours per day, and I can't spend a fortune on cR123 cells.
3. The entire assembly must be light enough to be supported by a spectacle frame.
4. I don't want to blow myself up.

Thanks in advance, 

Matt


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## saabluster (Nov 10, 2008)

drneale said:


> LED just won't work.


Just want to make sure that statement is one with an understanding of the state of the art in LEDs. There are now high CRI LEDs that are completely different from what 99% of people have seen an LED do. That includes people here.


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## ambientmind (Nov 10, 2008)

first, :welcome:
Next, I'll try to answer some of your questions. My first thought for this would be an LED build. I know I know, you said no LEDs but hold on. Have you heard of the warm white Crees or high CRI Seouls? These give an output similar and sometimes more pleasing than an incan bulb will and are much more efficient. That being said, the most simple idea I can come up with is making a headlamp using one of these LEDs and an aspherical lens to focus the light to a tight spot. Search on here for "aspherical" and you'll see what I mean. As for electronics, you could keep it simple but just direct driving the LED off of a single LiIon cell such as a 16430. Making it all look nice and fit on some glasses might be the issue. Maybe start with an existing headlamp with a reflector, remove the reflector and led and replace with the new led and aspherical lens. Just some ideas for you. Good luck!


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## LukeA (Nov 10, 2008)

What I would build:

1. Light source: Cree XR-E Neutral White or Warm White (This is an LED with color like incancescent while maintaining efficiency) behind an 8˚ optic. That optic will give you the light distro you want, and do it with very little spill light (however there will be a little). Based on my recent experience shining light into my eyes, you won't need more than about 70mA current to the LED. That's also good because that's very little heat to dissipate.

2. Power source: protected 18650. That will last a looong time running an LED at 70mA. Think like 35-40 hours between charges. 

3. LED on star with optic weighs 6.2g. I don't see the weight of the assembly on the frame needing to exceed 10g. The converter, switch, and battery can mount on the belt or in a pocket. 

4. Protected 18650s are pretty safe if you follow some precautions, like keeping the voltage above 3.5V - which a cheap multimeter will help you do. And you can recharge the cell before it's completley discharged, i.e. you could charge it every Monday morning and you'd never have to worry about over-discharge. You could also use 3 Eneloops in series for similar performance.

Construction note: an 18650 and the LED electronics and switch will fit nicely in a D-cell holder.


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## drneale (Nov 11, 2008)

Thank you all for your input. 

1. I am willing to try the warm LED. Is this one acceptable?
2. How about this collimator? 
3. How about this battery?


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## KowShak (Nov 11, 2008)

drneale said:


> Thank you all for your input.
> 
> 1. I am willing to try the warm LED. Is this one acceptable?
> 2. How about this collimator?
> 3. How about this battery?


 
Thats a "cool white" LED, not a "warm white" one.

http://www.cree.com/Products/pdf/XLamp7090XR-E_B&L.pdf

That PDF contains all the information for the XR-E binning codes, the graphs on page 7 show where it is in terms of colour.


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## Gryloc (Nov 11, 2008)

Welcome. It is great to see a variety of professionals seeking advanced lighting technologies. Could you tell us what budget you wanted to work with? Even though I love DX/KD for their selection and low prices, I think that so you can truly be happy with the finished product without any future reservations from using LED products, you should spend a bit more. 

Well, if that is truly a Cree brand optic (like the first that were available), then that seems to be a good choice. I have little experience with optics and Cree XR-E emitters (I worry about square-looking artifacts). So if you cannot find suitable optics, there are great reflectors out there that work well with the XR-E. I agree that asheric lenses, when slightly out of focus, would work swell for your application! They cast virtually no spill, and provide a very tight, but even beam. It may look ugly on a wall, but works great when actually being used. I believe saabluster would be the proper person to ask for more info on different sized aspheric lenses!  DX does sell some lenses that are made of plastic and are lightweight. The quality of the plastic lenses will be pretty decent, so you probably will not need any made of glass. 

As for the LED emitter, maybe you should shop around a bit first. Even though it is a XR-E Q5 WG emitter, you may find it to be too bluish compared to the warmer whites that you desired earlier. WH and WJ was the warmest of the cool white bins. I am not sure if you would enjoy the slow service (the shipping) of DX, either. There are several sources for other XR-E emitters around here at the CPF. Just ask (as I am not sure of the latest sources).

I remember reading a bit about neutral and warm white emitters, so I found those links for you...
Mudman CJ took some shots of an incandescent light source versus various high CRI emitters here:
https://www.candlepowerforums.com/threads/211911

saabluster took some shots comparing his WH cool white XR-E, his 5A XR-E, and his 6C MC-E emitters:
https://www.candlepowerforums.com/posts/2654418&postcount=269

To get an idea how the warmer of cool whites compare to neutral and warm whites, I stitched together two tint binning charts that DFiorentino created from X and Y data in this sticky thread. I hope he does not mind. They were scaled differently, and I did not have the original excel files, so I re-sized them and combined them using PSP8...



Notice that the WH/WJ tints overlap the 3A/3B tints slightly. With a neutral white (with a bin code from 3-5), you will be closer to that BBL line. The WH tint is pretty broad and can extend into the greens a bit. 

Well, I am not sure where to get a neutral white or warm white (besides Cutter), so maybe you can check with mudman or saabluster as to where they got their warmer emitters.

As for batteries: get the best. I am weary about even using those protected li-ion cells from DX. The protection circuitry could be set incorrectly, which can be a bad thing. Those cheap, Chinease cells are also often over-rated, and you can never be sure if they will work at all sometimes. I reccomend AW's li-ion cells (found on the CPF). He sells a range of sizes, and they are of the highest quality! They are not that expensive, either. Plus he stands behind his cells confidently. The capacity rating of his cells are right on with what you will really get, I believe. If you have the external pack located on your hip, then you could use higher capacity cells. His largest cell is a C-sized cell that sports a 3300mAh capacity. On the other hand, if you want to stay away from li-ion, then buy Eneloop brand AA cells (3 in series should work -2 may work at low current levels). Walmart sells Duracell rechargeables that are the Hybrid types. Look for the ones with a white color surrounding the (+) button. Those are from Japan and have a better quality than ones with a black colored surrounding. There are other brands of high quality hybrid AA cells around here as well. Again, just ask around!

I would reccomend that you use some sort of driver circuit to regulate your current output. However, if you will run the emitter at below 100mA from a li-ion cell, you may be able to get away with DD with a resistor to reduce current. If the power is low enough, you may be able to use a linear variable resistor to dim the LED as needed. A cheap and simple linear voltage regulator would also work (using a potentiometer to dim the LED) since the operating efficiencies are not as dramatically important with these low current levels. Either way, you will get some great battery life if the currents are this low. 

LEDs are very efficient, so the amount of power required is so much lower that what you may be used to with a light bulb. Well, due to the efficiencies, I think that with such a narrow beam, currents above 100mA will create enough light that can be uncomfortable for the patient. With several hundred milliamps, it is possible that you could do some damage as well . That would sort of go against your entire profession, wouldn't it? I say that once you get your LED and optic set up, experiment with current levels to see which provides the correct amount of lighting.

-Tony


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## LukeA (Nov 11, 2008)

Gryloc said:


> Welcome. It is great to see a variety of professionals seeking advanced lighting technologies. Could you tell us what budget you wanted to work with? Even though I love DX/KD for their selection and low prices, I think that so you can truly be happy with the finished product without any future reservations from using LED products, you should spend a bit more.
> 
> Well, if that is truly a Cree brand optic (like the first that were available), then that seems to be a good choice. I have little experience with optics and Cree XR-E emitters (I worry about square-looking artifacts). So if you cannot find suitable optics, there are great reflectors out there that work well with the XR-E. I agree that asheric lenses, when slightly out of focus, would work swell for your application! They cast virtually no spill, and provide a very tight, but even beam. It may look ugly on a wall, but works great when actually being used. I believe saabluster would be the proper person to ask for more info on different sized aspheric lenses!  DX does sell some lenses that are made of plastic and are lightweight. The quality of the plastic lenses will be pretty decent, so you probably will not need any made of glass.



I popped a KD 8˚ on a Cree last night and it didn't have any artifacts at .5m. I don't know is an aspheric is called for here. It's heavy, it needs to be mounted just so, and it has chromatic abberation at the edges of the beam. And there's no guarantee that the aspheric lens will have an even projection of light at 8-12˚ and .5m. These optics don't have any of those problems.


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## LukeA (Nov 11, 2008)

drneale said:


> Thank you all for your input.
> 
> 1. I am willing to try the warm LED. Is this one acceptable?
> 2. How about this collimator?
> 3. How about this battery?



1. Cutter.com.au sells warm Crees. DX/KD don't.
2. That's actually the one I meant to link to. I changed the link in my post. (the 10 pack is a much better deal per piece)
3. That would work, but these are four or five times more capacious in only a slightly larger volume. I don't own AW cells and I've had good results with the linked cells. I guess you could say there's two factions on CPF when it comes to li-ions (and everything else :nana. One group uses DX/KD cells, the other group looks at the first group like the first group is witches and uses only AW cells.

There's also LiFePO4 cells, which will be safer than any li-ion but have less capacity.


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## LukeA (Nov 11, 2008)

Gryloc said:


> I would reccomend that you use some sort of driver circuit to regulate your current output. However, if you will run the emitter at below 100mA from a li-ion cell, you may be able to get away with DD with a resistor to reduce current. If the power is low enough, you may be able to use a linear variable resistor to dim the LED as needed. A cheap and simple linear voltage regulator would also work (using a potentiometer to dim the LED) since the operating efficiencies are not as dramatically important with these low current levels. Either way, you will get some great battery life if the currents are this low.
> 
> LEDs are very efficient, so the amount of power required is so much lower that what you may be used to with a light bulb. Well, due to the efficiencies, I think that with such a narrow beam, currents above 100mA will create enough light that can be uncomfortable for the patient. With several hundred milliamps, it is possible that you could do some damage as well . That would sort of go against your entire profession, wouldn't it? I say that once you get your LED and optic set up, experiment with current levels to see which provides the correct amount of lighting.
> 
> -Tony



I have a limited understanding of electronics, so I was thinking about a 2-mode AMC7135 board running on low with 2 AMC chips removed to give 50mA. A resistor/pot might be better; I don't know if 50mA is enough and the increments you can get with that board aren't narrow.


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## clg0159 (Nov 12, 2008)

KD does sell a warm white led (Cree P4), look here:
http://www.kaidomain.com/ProductDetails.aspx?ProductId=5568
If you are willing to wait, and wait, and wait
They claim 3000K but do not specify the color bin


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## LukeA (Nov 12, 2008)

clg0159 said:


> KD does sell a warm white led (Cree P4), look here:
> http://www.kaidomain.com/ProductDetails.aspx?ProductId=5568
> If you are willing to wait, and wait, and wait
> They claim 3000K but do not specify the color bin



I had forgotten about that LED. Definitely worth checking out. The LED in the pictures has the warm white phosphor. But I can't be sure which bin it will be. 7C and 7D are 3000K, but I haven't seen a P4 yet with that tint. So it might be N2/P3 7C/7D or P4 7A/7B. But those bins are very similar. After all, they're all adjacent to each other on the binning chart.


The image below is a Q5 WC in series with a P4 7A (3200K) at 350mA. (P4 7A is on the left)


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## clg0159 (Nov 12, 2008)

How about just a simple micropuck 350/400/500 ma
http://www.ledsupply.com/micropuck.php
and 2xAA eneloops with the KD warm white and optic. *Simple*, sturdy,no li-ion concerns, and should achieve more than enough runtime.


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## LukeA (Nov 12, 2008)

clg0159 said:


> How about just a simple micropuck 350/400/500 ma
> http://www.ledsupply.com/micropuck.php
> and 2xAA eneloops with the KD warm white and optic. *Simple*, sturdy,no li-ion concerns, and should achieve more than enough runtime.



Even 350mA is about 5 times the necessary current. I shined myself in the eyes with 150mA and it was way too much.


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## drneale (Nov 12, 2008)

Okay. Thanks for your patience with my inexperience. I thought eye surgery was complicated--but flashlights are brutal!

1.I'm going to order the Cree MCE4WT-A2-0000-000HF8 Warm white, 280 min lumens, F8 (7C, 7D, 8A, 8B) from cutter.com.

Since most of the time I am using the light to differentiate between subtle shades of red, orange, and yellow, and shorter wavelengths are more prone to chromatic aberration, I am going with my intuition and selecting the yellowest light available. Thanks for that graphic with the spectra of each LED.

2. I'm going to focus the beam with: 




_*120/147
*__6 Degree LED Collimator Lens.__ Designed to operate with Cree Xlamp 7090 High Power LED’s High light collection efficiency of >85% Precision moulded in optical grade Polycarbonate for thermal stability and system durability Part of the Polymer Optics “Modular LED Optics”® range _
_ Comes with the Optic Holder 147
_I know it says it is designed for Xlamp, but I'm hoping it will work with MC-E as well. Is this a foolish assumption?

3. As far as the battery goes, I have been pushing toward smaller cells, because I want to fit everything on the spectacle frame. I would be really happy with a 2-4 hour run-time if a rechargeable could easily be swapped out. Its not like I'm out in the wilderness or anything; I could just keep a few spares in the desk drawer.

4. With respect to a driver circuit:


I understand that I probably won't need high amperage; thus, I can probably get away with a variable resistor (10K?) without sacrificing too much efficiency.
However, gear-lust is tempting me. If I DID go down that road, would this product (*Boost and Buck Circuit For CREE XR-E Q5 LED) *suit the application? It is tiny, light, and should provide about the right current off the shelf...right? Would the extra weight and expense return a significantly longer battery life and consistent illumination?
5. Budget. Since the commercially available products retail for $2000 minimum, I am comfortable spending a few extra bucks on a quality emitter. Plus, even the most compact devices have a belt clip battery. I think we can do better for far less money.

Again, your help has been invaluable.

Matt



_
_


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## DM51 (Nov 12, 2008)

Very interesting project, drneale - please keep us up to date as it progresses.


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## saabluster (Nov 12, 2008)

drneale said:


> 2. I'm going to focus the beam with:
> 
> 
> 
> ...


You do not want to use that with the MC-E as it will have four separate beams due to the fact that the MC-E is made up of four dies. Trust me I have those and have first hand experience. You either want to change to the XR-E which you can get in warm white from cutter as well or change to the polymer optics number 186 which is the same as the one you put a picture of up above except it has a diffuser on the face to smooth the four beams. My recommendation is to get the XR-E. As I understand it you will not need the higher output from the MC-E and you will probably have to wait on MC-E specific optics as they are not shipping right now.


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## gillestugan (Nov 12, 2008)

Hi, I have the http://www.kaidomain.com/ProductDeta...ProductId=5568

It is really nice with very uniform tint. Best warm white I've had. 

Can't tell what tint it is, as I have no other warmwhite to compare with, but probably around 3200k. Received the emitter in 12 days, much faster than DX.

I really cant see why you would like a MC-E. You will have problems finding really narrow optics for MC-E and the light output from a single XR-E will surely be more than enough.


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## saabluster (Nov 12, 2008)

gillestugan said:


> Received the emitter in 12 days, much faster than DX.


That would most certainly be an anomaly.


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## LukeA (Nov 12, 2008)

saabluster said:


> That would most certainly be an anomaly.



My KD orders take much less time than DX (and Cutter).

As for the MC-E, it's not the best choice. As saabluster mentioned, you will have a dark cross in the beam and you will have waaaay too much light which you won't be able to focus the way you would be able to with an XR-E.


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## AilSnail (Nov 13, 2008)

edmundoptics have some fresnel aspherics. That is a flat sheet with grooves in it to make it work like an aspheric. 
You can easily do the math of the runtime once you know the amperage; an explosion safe Li-mn AW 123 has .55Ah x 3.7v and the LEDs work between 3 and 4v so at .1A with 80% efficiency it should last for 4-5 hours.


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## AilSnail (Nov 13, 2008)

I don't know the current of that converter you posted drneale?

efficiency of a linear converter or resistor would be the difference in voltage, so worst case 4v (battery) to 3.3v (low Vf I think) or something; 82%.
You probably won't get alot better with a cheap converter? But consistent brightness is nice though.


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## Roland Gama (Nov 13, 2008)

I am a dentist and in the process of building one for my dental loupe.
I have used a cree XR E cool white led Q5 bin mounted on a pcb with the base and tube constructed of aluminium. The optics are clear 8 degree spot which gives a great three inch spot on the working distance. 
Not yet finished with the battery housing. It works great with any lithium battery driven directly. May use a driver from the luxeon range if needed though its okay without one.
The ready made ones cost the equivalent of 600 usd while these cost me on 10 usd!!!
Also use the same loupes for small soldering jobs, etc.


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## saabluster (Nov 13, 2008)

Excellent work Roland! Way to take the matter into your own hands.


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## TigerhawkT3 (Nov 13, 2008)

I assume all you DIY dentists have spoken to your respective attorneys before using your homebrew equipment? In the video industry, there's a reason a showerhead 5mm array with a dimmer costs over a grand, and that reason is liability. I would expect the situation in the dentistry industry to be even more severe.

That said, nice lights.


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## Gryloc (Nov 13, 2008)

Dang it, Tigerhawk, you bring up a point that is too good. The sort of sobering aspect of DIY in any professional field. It ruins the fun of saving money by building the parts yourself, but by using the expensive and licensed equipment, you could be saving much more than what bad can happen if you get that one sour patient who isnt happy with your diagnosis after using your medical tool.

Well, more power to you if you plan on using the device in another country where conditions are not ideal for such expensive equipment, or where there is little electricity. However, I am hesitent to agree that this would be a good solution for any licensed doctor anywhere in the States, regardless to hospital size or budget, especially if this is encouraged by the firm to trim a few dollars here and there from equipment or operating costs.

Now, if this home-brew device is used along with the expensive equipment to confirm it works fine, or if this is used to check something routinely that does not really require an elaborate and calibrated system of optics, then why not? Do others in the field do any alternatives like this? If you notice other optometrists using Mini-Maglites with a set glasses with magnifying loupes, then this solution has to be miles better. I do not know. I guess that we need more input from drneale. 

-Tony


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## drneale (Nov 13, 2008)

Okay, I placed an order at Cutter. I settled on a P3 Flux 8C Tint(2900k), along with various optics, driver, switches, etc. When I get them in my hot little hands, I'll give you all an update. Thanks again for the help!!

Matt


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## drneale (Nov 13, 2008)

TigerhawkT3 said:


> I assume all you DIY dentists have spoken to your respective attorneys before using your homebrew equipment?



The point is interesting, but far from sobering. Our optical equipment is not licensed by any governing body. We buy the tools that work well. Period.

This piece of equipment, as I stated above, is a glorified flashlight. The only other function of the binocular indirect ophthalmoscope (BIO) is to reflect the light path of each eye so that they are only 10mm apart, as opposed to ~65mm. That was easy to accomplish, as custom sized optical grade first surface mirrors are readily available, thanks to the web.

The only optical lens I need is held in my left hand while I examine the patient. It is a $200 double aspheric lens, and you are right--I could never DIY one of those.

Also note that Roland is using commercially available loupes--there is no substitute for excellent lenses, but light sources are a completely different matter. Technology is advancing at a breakneck pace, and current manufacturers simply haven't capitalized on the technology that is discussed here at CPF.


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## Gryloc (Nov 13, 2008)

I suppose that I get too carried away. I guess it is fine, as long as you do not fabricate surgical tools or anything. I am sure that you will run your finished project through its paces. We will be here when or if you feel that something on your setup has to be tweaked or modified. It is good that you got a variety of parts to try out. In the spirit of CPF, if you are concerned by which LED, optic, or flashlight will suit you best, then buy both. Any circuit can be modded somewhat to change current, and you should be able to find a decent optic. Well, I look forward to when you get your stuff in the mail.


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## TigerhawkT3 (Nov 13, 2008)

drneale said:


> The point is interesting, but far from sobering. Our optical equipment is not licensed by any governing body. We buy the tools that work well. Period.
> 
> This piece of equipment, as I stated above, is a glorified flashlight. The only other function of the binocular indirect ophthalmoscope (BIO) is to reflect the light path of each eye so that they are only 10mm apart, as opposed to ~65mm. That was easy to accomplish, as custom sized optical grade first surface mirrors are readily available, thanks to the web.
> 
> ...


I didn't mean to step on anyone's toes. I just wanted to recommend getting real legal advice before using a device on your customers that may not even be UL listed. Just a thought.


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## Roland Gama (Nov 14, 2008)

Gave a thought to all the points mentioned and it has boosted the impetus to diy. I only would like to clarify that I am not a DIY dentist but rather a dentist into diy. Here is pic of another battery holder design. Its a four cell series design and the polarity at the tip can be changed by reversing the battery connection. Works excellently. Cheers!!!
http://i157.photobucket.com/albums/t60/rolandgama/Photo-0001-1.jpg


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## drneale (Nov 20, 2008)

Here are my latest results using: 

1. Cree XR-E warm white
This LED was perfect. The quantity and quality of the light are ideal.​2. L2 6 degree collimator
The so-called 6 degree optic produced a 10 inch spot at thirty inches with a wide spill. This correlates to an 18 degree pattern--just for the spot. Not exactly what I had in mind. The same supplier sells a 2 degree optic, but I expect it will have the same spot+spill pattern. Any suggestions out there? Should I pursue an aspheric lens, knowing that it will require precise positioning and will add mass? ​3. Buck puck 350mA with pot
This operated as advertised, but was ugly and bulky. Plus, it requires 5v to operate. I would ideally like to run my light off a single lithium ion cell. Any ideas?​4. Prismatic lithium ion battery
This is apparently a new technology that provides a better charge/mass ratio. Plus, I like the form factor of a rectangular battery better than a cylinder. Any comments?​


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## LukeA (Nov 20, 2008)

drneale said:


> Here are my latest results using:
> 
> 1. Cree XR-E warm white
> This LED was perfect. The quantity and quality of the light are ideal.​2. L2 6 degree collimator
> ...



That optic lists a half-angle measurement. This one is a full-width-half-maximum angle measurement (aka full beam width) of 8˚. There will still be spill, but there's not very much, especially at low currents. If you want zero spill and are ok with chromatic aberration and positioning the thing in 5 axes (x,y,z,rx,ry), then an aspheric may be for you.

Yes, li-poly batteries are lighter, but that one has 1/3 the capacity of a 18650 and also does not have a protection circuit (I don't think any li-poly does). You could go multi-cell with the battery to satisfy the buckpuck, but then you would have to watch for overdischarge. The buckpuck can run a 2-cell lithium pack doen low enough that charging might cause an explosion. 

I think you want a resistor and a pot to vary the current.


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## gillestugan (Nov 20, 2008)

Good to hear you are satisfied with the LED.

Regarding the driver: 
You can use 7135 based driver when running off a single Li-ion. They are cheap and will give you several levels. 
Available from DX and KD. I have this one: http://www.dealextreme.com/details.dx/sku.7612 which have a 3 level mode. it is 17mm in diameter and about 3mm thick.
If you want a maximum of 350mA you can desolder two of the three 7135 chips.
That will give you about 350mA on max, 120mA on medium and 35mA on minimum. 

I think you should go with the aspheric lens. As you have more power from the LED then you are going to use, you don´t have to vorry about collecting 100% of the light. This means you can use it without a reflector. Just put it in front of the reflector where it gives the desired beam. 
DX have cheap lightweight acrylic lenses in various diameters and focal lengths but I don't know if any of them is suitable.


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## saabluster (Nov 20, 2008)

drneale said:


> Here are my latest results using:
> 
> 1. Cree XR-E warm whiteThis LED was perfect. The quantity and quality of the light are ideal.​2. L2 6 degree collimatorThe so-called 6 degree optic produced a 10 inch spot at thirty inches with a wide spill. This correlates to an 18 degree pattern--just for the spot. Not exactly what I had in mind. The same supplier sells a 2 degree optic, but I expect it will have the same spot+spill pattern. Any suggestions out there? Should I pursue an aspheric lens, knowing that it will require precise positioning and will add mass? ​3. Buck puck 350mA with potThis operated as advertised, but was ugly and bulky. Plus, it requires 5v to operate. I would ideally like to run my light off a single lithium ion cell. Any ideas?​4. Prismatic lithium ion batteryThis is apparently a new technology that provides a better charge/mass ratio. Plus, I like the form factor of a rectangular battery better than a cylinder. Any comments?​


The latest LEDs are pretty awesome aren't they? I have a lens that would work perfectly. It is 2mm wide and weighs about 1 1/2 grams(very light). Contrary to popular belief it is very easy to focus and is much more insensitive to proper centering than reflectors. I can send it to you for free if you want. Just PM me. I agree with your battery choice but suggest you look at some of the dedicated online battery places. You probably could also just use the very small 7135 driver boards if you are going to stick with one cell. If you look around some of the online battery shops you will also find over/discharge protection circuits so you protect your battery from going .


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## AilSnail (Nov 21, 2008)

like I said, edmundoptics fresnel aspheric. I've got the one which is 1.5x1.5"(1"dia), 0.6" back focal length. it is very tight. A square with about 8-10cm sides from 1m distance. shipping to Norway was more than the lens.

There is not much difference in wh/grams between li-po and li-ion 18650.
16350 is less energy dense. li-ion have longer life, I think.
If your li-po cell is not protected, and you are using a converter capable of sucking all the juice without warning, you might want to add a protection cirquit at the least. Available from many places which sell batteries.


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## BobVA (Nov 22, 2008)

If you haven't found it yet, this thread on high CRI LED's may be of some interest, particularly BabyDoc's comments on their use in a clinical setting:
https://www.candlepowerforums.com/threads/199054

Welcome to CPF!

Bob


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