DIY High Intensity LED Ring Flash

[Paintguru]

Hey everyone,

Stumbled upon this site while doing a search for high powered LED ring lights. I'm trying to build one for a little project I'm cooking up where I want a LED ring flash that can give me enough power to stop motion a moving macro subject while my macro lens is set at maximum f-stop (minimum iris size) to provide maximum DOF. Not surprising, this requires quite a few photons!! I want to use LEDs due to their long life (I will be firing these every 5-10 seconds for almost 12 hours a day, 5-7 days a week, all year long). While a xenon flash has been shown to work for me (standard studio strobe), I have a feeling at this desired work load, I would be changing the bulbs much too often. Nothing out there that I have seen in pre-made LED flashes can come close to this. However, I stumbled across another post here that discussed some newer, high powered LEDs on the order of 100-300W chips that put out quite a few lumens. I'm wondering if an array of these in a ring configuration, fired in strobe mode, would work for me. Part of my problem is that I'm not the most electronically gifted person (I can do some simple soldering), nor do I know what is needed to simply strobe these LEDs (which would also avoid heat issues). I'm just beginning this project, so my main research has been through Google. If folks out there have any suggestions or resources that may help, I would greatly appreciate it. Thanks!

 

[mrb]

Hi Paintguru :welcome:

Interesting project but the problem with high speed photography is you need an awful lot of light, even more so if the need for good DOF is stipulated.
I've seen the figure of over 500,000 lumens quoted for a canon speedlite 430ex fired in 1/1000th sec. To get this equivalent from LED technology is not going to be easy or cheap.
Many of the super high power "hundreds of watt LEDs" are low efficiency/output chinese examples.
Even with a super array of 20 luminus CSM-360 rated at up to 6000 lumen each you are not going to be close to a studio flash/strobe since you are dictated by the very short shutter time.

What ISO will you be using?, some of the newer models are offering crazy high values and if you can get away with doubling or more the ISO then at the same shutter then only half or less the light is needed for same exposure, subject to reciprocity/noise issues of course, could make the difference of this being viable or not.

Some other posts about 100watt leds here.
Some more discussion of flash lumens here.

 

[Paintguru]

mrb,

Thanks for the reply. I know this looks to be quite a job for these LEDs to accomplish, but I figured it was worth a shot, regardless of cost, as the cost of replacing xenon flashes would likely fast approach the cost of the LED unit.

A few comments to your thoughts and questions. One reason I don't think I need quite as much light as a studio flash puts out is because the way I have it setup now, I'm really wasting quite a bit of the light produced by that flash. I think my spread angle on the reflector is ~100 degrees, and it is set back a good 12-15" from the target, so a lot of light is missing the image area. From my measurements, I'm thinking I need 1.5 million Lux in order to get my exposure to work out correctly (I'm going to recheck this number though). I was hoping focusing all my light just into my image area would allow me to hit this intensity number.

A little about the camera, it is not a typical consumer DSLR camera. It is a more rugged industrial camera, as I need it to be a bit more robust. As a result, it doesn't have a standard ISO setting (I can adjust the gain). Upping the gain does help a bit, but not as much as the prosumer cameras.

Thanks for the links you provided; I will check them out.

 

[NYCaver]

I would be worried about color rendition. I doubt any very high power LEDs are going to also be neutral white, and have a high Color Rendition Index (CRI). From what I've seen only high CRI Nichia's seem even remotely up to the task of faithfully rendering colors to the level that a studio strobe can. You'd need a bucket load of those to get the kind of light level needed for freezing motion at maximum f-stop.

 

[Darkhorse85]

LEDs are up to the task.
More and more manufacturers are producing high-CRI white LEDs. Nichia, Seoul Semi, etc.

You dont need to produce as much illuminance as a xenon, just as much Lux by time as xenon for however long the shutter is open (lux.sec). Total light energy hitting the image sensor is what's important. LED's can be 'pulsed' to very high currents for however long your shutter will be open. This will be much longer than the microseconds of a xenon.

The only caveat is that the LED flash still wont 'freeze' action shots like a xenon strobe, but Ring flashes are more for portrait photography anyway.

Go for it!

 

[mrb]

I totally agree that LEDs are easily up to the task if you have more exposure time to play with.
If the OP's aim is to freeze/stop motion then a longer exposure from less bright source just isn't really available.
Certainly would be interesting to find out just how hard a pulse some of the new monster arrays are able to sustain though!

 

[kmossman]

We have access to a 100W LED matrix, and by the end of February - once the final tests are done - to a 200W LED matrix.

If you are interested, can provide price and specs.

Do note, however, that the power requirements are considerable! For 100W you are looking at nearly 10A, so you will something other than the normal power supply.

Ken
VKElectronic

 

[NYCaver]

I'm confused. Didn't the OP say he needed to freeze motion? Obviously, with enough exposure time any light source will illuminate your photo.

 

[Mike V]

I kind of doubt that LED is going to give you the intensity you require, but LED ring lights exists:

For example the Litepanels Ringlite Cinema:

http://www.litepanels.com/lp/products/ringlite_cinema.html


The Fisherlight:


http://www.fisherlight.com/ringlite.html


There are quite a few others.

 

[NYCaver]

I see a rating of 1100 lux at 5ft for one of those ring flashes. They are more for portrait photography where you can be more loose with the f-stop.

Maybe you will get near the needed brightness with more than one of these 100W or 200W super arrays people are talking about combined with some tight focusing of the light. However, these are all about brightness and not producing photo quality light. It's important to consider that a ranging from a small hot shoe flash to a big studio strobe we're talking from 100's of thousand to hundreds of millions of lumens over the space of around 1ms. They're not focused, but those are huge numbers.

Sorry, not trying to rain on the parade. Just getting the facts out. I wish you all the best luck.

 

[Magic Matt]

Fascinating topic! I think a traditional flash will still work better though...

I'm confused. Didn't the OP say he needed to freeze motion? Obviously, with enough exposure time any light source will illuminate your photo.

I agree. I think most flashes last about 1/1000th. As far as I can see there will be a considerable timing issue to contend with if you use LED illumination over a longer time frame.

The shutter speed of the camera will affect how the shutter curtains are synchronised. With a flash, it's not unusual to use a slow-ish shutter speed of 1/60th to 1/250th depending on the amount of ambient light you want etc. Even at 1/60th, the amount of the exposure which is lit by the flash is usually only 1/1000th. At faster than 1/250th (ish), one shutter curtain is already closing while the other is still opening.

If your LEDs were lower intensity than the original flash, and using a longer exposure, you may well get movement smearing in your images (not quite the same as motion blur). As an example, at 1/60th, all parts of the image plane will be exposed for 1/60th, but not necessarily at the same moment in time.

If you look up information about rolling shutters etc. it may help you decide how to best tackle the problem. If your subject is stationary or only slow moving however, you wont have the problem.

You can find a good example of the effect by way of a video clip on this page, about 1/3rd of the way down.
http://www.dvxuser.com/jason/CMOS-CCD/

 

[Gunner12]

Don't some LEDs have a rated pulse current? At that current the LED should have more output but because the on time is short, the LED should be fine.

As the above posters have said, you'll need a bunch of good color rendering LEDs and some kind of focusing mechanism.

What's the area of the surface being lit up?

 

[SemiMan]

Love LEDs, would not use them for this application.

Your studio strobes are designed for a very high intensity in a small space. To that end, they are driven very hard and have limited life... 10,000 pulses or so.

Xenon strobes designed for industrial purposes can be quite powerful, but generally not as compact. They have lives measured in the 10's of millions of flashes which will be enough at once ever 5-10 seconds to last years.

Semiman

 

[aUtOnOmOuS_Robot]

I've routinely pushed 1A+ through common 10mm "super bright" leds (rated ~100mA) at 10% duty cycles to perform background subtraction with image processing algorithms. I haven't tried this with any of the bigger leds but I don't foresee a problem. You are probably already aware of the use of capacitors in camera flashes. Super capacitors are the way to go for larger systems. This will dump a lot of energy into your leds very quickly.

 

[kmossman]

There ought to be a MAX instanteous current rating on the datasheet. The 100mA figure is for continuous current.

How did you control the duration and current?

Ken

 

[NYCaver]

Is color shift due to higher currents instantaneous? If so, over-driving for a short duration could raise the color temp of a neutral LED to be too high, right?

 

[Magic Matt]

If you're shooting digital that doesn't really matter too much, since you can always correct for that afterwards.

 

[DM51]

CPFer Packhorse has made just such a ring-flash unit: Ring of Light (thread in Dive Lighting section).

 

[NYCaver]

If you're shooting digital that doesn't really matter too much, since you can always correct for that afterwards.

I don't think that's necessarily true. You can definitely make it much better in post, but if you are only illuminating one end of the spectrum, it's kind of hard to make it look like the other end of the spectrum is being correctly reflected when it wasn't in the first place.

 

[SemiMan]

I don't foresee issues in vastly over driving high powered LEDs for short durations, the only problem is that there is limited benefit beyond a certain point. The output starts to plateau. Fortunately the short pulses do not raise the heat much so you do not get output drop due to heat...well at least not much.

Semiman