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Need help with LED lighting. Answered

Trying to make a bright LED light for application with a dental loupe.
I see tons of LEDs and diodes and new flip chip technology. It's all very confusing. I'm basically trying to make the brightest light in the smallest application. It will be mounted on a pair of glasses with a set of loupes on them. I don't want the diameter to be any more than 1 inch.
I found a website that can cut a lens to any dimension I desire. I basically want a spot beam that will be about 5 inches in diameter from about 18 inches in distance. It will have to run off some sort of battery pack.
I was thinking of just taking a LED bulb element from a flashlight and slapping a lens in front of it to focus the light. Really not sure what type of LED bulb to buy or if it might be better to build my own. I see companies advertising their LED dental loupe light at 8,000 lumens which seems fairly impossible since most diodes seem to only be rated at 100 or 200 lumens at the most.

Any advice or guidance would be greatly appreciated.

Thanks in advance....




Best Answer 8 years ago

I would recommend starting with an existing quality loupe, and clamping your diy light on the bridge somehow:

One single 1-watt led would be extremely bright.  Going bigger than that would basically result in overheating your forehead, as they do get quite hot even with a heatsink.

Example parts from Dealextreme - I love these guys, free shipping and super duper cheap stuff!
Cree Q5 LED $5.50 ea
23.36mm Optics for that led $3.94 for a 5-pack.  This is the lens and reflector to make a ~8 degree beam
Power Supply is important to regulate the current to the led and make sure it doesnt explode. Takes in battery power and outputs   This particular one inputs 1 or 2 AA or AAA batteries and outputs the 3.6 volts needed for that led.

Browse their stuff - and just match the parts with one another by their requirements; voltage, amperage, and size.

Great!! Thanks for the advice. I appreciate you taking your time.

So I ended up buying everything yesterday. But now I am thinking I might have gone overboard. Here is what I got.

I got a cree xp-g bulb with a buckpuck 1000ma driver and Lisa optic . It says it puts out 5v and that it needs more voltage than that to drive it. So I was thinking of getting a 7.2V battery pack, but I wasn't sure how much amperage I would need to drive it. Preferably I would need about 4-8 hours of run time per day.

The loupes I already bought and I was looking into finding a small housing for the 10mm optic. I was thinking of maybe trying to find a small maglite and using just the front part as the lens holder. The lens was 13% which I figured will make about a 5-6 inch spot from 16" away. I also need to find a small mounting bracket so I can bolt it to the bridge of the loupe. If you have any further advice, it would be appreciated. Thanks again!!!!

I looked at the page and your link points to item number ending 995 - makes me think its the 17 degree model, which is still a decent angle for your application.  It might be good to experiment with a few sizes; especially with something that can adjust 'zoom to throw'.

Good luck with your project, and if it works, photograph EVERYTHING and write an instructable :)

A buck puck is often upwards of 80-95% efficient for a linear load like an led...Are you sure the led you bought takes 5 volts?  You want to match the driver closely with the requirements of the led.

To figure runtime, you use a few numbers - and the buck converter just adds another factor:
1 amp current at *I think its less than 5 volts* example 4 volts is 4 Watts, times 8 hours is 32 Watt-hours.  Add in a conservative 20-50% squish room for efficiency and safety margin; you get 'around 45-50 watt hours'

Batteries are rated for volts and (milli)Amp-Hours.  You decide what voltage, say 7.2, and divide the watt-hours by this to get the required amp-hours.  (in case its not obvious and I'm talking gibberish: a watt is 1 volt-amp, or a watt-hour is a volt-amp-hour; standard algebra rules apply)
50/7.2 = 6.94 amp hours, or 6944mAh.  Simply chain enough batteries in series to make 7.2 volts, then chain sets of those in parallel to add up to the 7Ah.  The neat thing about buck converters is you can run higher voltage or amperage - so long as you make up the watts somehow.

Hmm, I think the lens is the 13 degree because it says RS in the name and the data sheet says the RS is the real spot which is 13 degrees, but either way from a close distance it should still work. As far as the led i'm not sure. The data sheet says that max voltage @350ma is 3.75 but doesn't say what it is at 1000. I don't think Cutter has shipped by order yet, so do you think I should change the driver? Let me know and thanks again for the help. I'm feeling confident and will definitely do a write up as I start assembling. Thanks to all the great people on this site I was able to figure it out. Check out the housing I found from a maglite. It has a 12mm diameter which will fit the 10mm lens just perfect. It's going to be super bright and super small. Loupe lights sell for $600-$800 bucks. I'm gonna pull it off for just about $100. Woohoooo.


Forward voltage (@ 350 mA) V 3.0 3.75
Forward voltage (@ 700 mA) V 3.2
Forward voltage (@ 1000 mA) V 3.3

Those are Typical values - try not to run at 'max rated' for too long, or you will be a sad panda :)  at most you want to feed this 3.3 volts to pump the proper current through.  That buck seems it might do the trick;   It outputs a 5v reference that can be fed back into the 'control' pin to make variable brightness...

Hey man. I'm back again. Again I really appreciate you being so helpful. So I've been looking for battery packs but I'm having a hard time. I took a look at someone's light today and they have a 7.4V 6600mah Li-ion back that is fairly small (clips on a belt). Anything in that capacity range that I'm finding is HUGE? I did find some slim 1 cell packs but they all seem to be 3.7 volts. Can you shed some light (no pun intended) on the situation. 3.7V should work with my driver right (I would just have to step up the capacity) or maybe I'm just going to have to live with the light only lasting 4 hours?

it is true that 7.2v 6Ah batteries wouldn't be tiny.  Might be best to have a swappable battery pack for the convenience/size.

That buck converter needs MORE than the output voltage as an input.  The driver you selected is far 'larger' in capacity and size than you need.  I can't suggest one in particular - but I'd be inclined to think you want one capable of boost, so that you can use 1  (3.7v) to power the single 3.3v led.  Adding more batteries in parallel adds capacity.

Sidethought:  I just bought some very small cree flashlights.  They fit one AA...for size comparison; and it runs for 2 hours on 1 lithium battery.  (by specs).  Again, the head screws off and would function as a light unit that you just run a wire to the back to a pack on your belt.

Actually I think I was wrong. It doesn't seem like it supplies 5V. The 5V was if you need to power a circuit board with it. Here are the specs. It doesn't really say the voltage, but they suggested for the LED. What do you think?

With the Cree or Luxeons, you can get that kind of beam spread from their stock optics.


Sweet thanks for the advice. So I'm assuming with these I would have to build the circuitry. Also I'm not really sure what the drivers are. So for example when you buy a drop in led bulb into a flashlight for example, those have the drivers built in? Also what do you think about the lumens I mentioned. Do you think those numbers these companies are posting are baloney?

Lumens and Candela are often confused.

The circuitry is straightforward. You can buy it off the shelf, or make your own, depending on how small you need to make it.

Big LEDs like Crees need special high power drivers.

So I've been searching some more, and the one that seems to keep coming up is the luxeon III 5W. I see they come on a star shaped circuit board, but most seem to only have one. Can you put more side by side or is one just ridiculously bright? So for example one dental louple light I found states that it is 8,000 footcandles or 86,000 lux. So when an LED says it is 200 lumens, is that lumens per sq cm or inch or foot??? Sorry to keep bugging you but I really have no idea about this stuff.

A foot-candle is the perceived BRIGHTNESS of one candlepower (1 lumen) at 1 foot.
The LUX is total light output in lumens - by my understanding...

1 watt laser outputs enormous brightness but not a lot of total light
1 watt LED over 180 degrees puts out plenty of light, but not a lot of brightness at any given point (in a relative sense).

One is IMHO obscenely bright...especially from 18" away. I mean seriously, dangerously bright.

Light units are pretty tricky things to get your hand around. The Wikipedia pages aren't bad

Try this

Color also matters. If you will be working on living tissue the wrong color will make you screw up, not notice things you should see, etc. LEDs are not  "full spectrum" and some things become invisible without the right wavelength.

Hmm, good point. Thanks...

Cool. Now I'm getting somewhere. The Cree XR-E Q5 seems to be popular. Do you think that would work? Also now I'm trying to find some sort of housing and battery pack since most of these seem to be replacements for flashlights. Any advice?