using high power led's in place of a flash bulb

[z_slimmy101]

Hello all, i looked around and couldn't find a thread that answered this question so here it goes, i'm trying to replace a 250 watt flash tube with 10 or 15 high power led's the ones that give out like 2000 lumens each. Has anyone tried this or know if it will even give enough light. I can't seem to find how many lumens a dynalite RB-1000 gives off when it flashes. Any help will be much appreciated.

[Jason_Killbourn]

I'd really like to know the answer to this too... Well, more specifically whether anyone considered it feasible to fit sufficient hi-power LEDs to generate at least 10000 lm (or much more if possible) into a space of approximately 10cm dia?

The simple reason for this being that I've grown tired of blowing up strobe lighting at work (I have a sizeable graveyard of monobloc heads sitting on a shelf in my studio with fried capacitors) and would love to be able to build an LED alternative that could still use a Bowens S type mount for my light modifiers (hence the 10cm dia restriction). Having had a fair old search of the photographic forums, I figured somebody on here would have a much better grasp of the technical know how and hardware available for such a project. In terms of requirements, it would need to be a wide angle as opposed to a tight beam. It wouldn't need to flash, but a dimmer would be necessary. It would be run from a transformer (though a battery powered option could be quite interesting) and any advice regarding heatsinks and fans would be ever so much appreciated.

Thank you in advance for any replies

[Lawliet]

I used a bunch of Cree XP-Gs for a high speed flash - if used as a flash(+low powered modelling light) you can get away with a metal core PCB as a primary heat sink. That would be about 20klm of a 6x6cm area.Thermal management gets interesting once you want a video light.
But there you have to ask yourself: why concentrate the light in a small source you have to widen up anyways? Look at the Kino Flo products for inspiration and spread the LEDs. You avoid wasting about 3/4 of the light for starters...

[Jason_Killbourn]

I used a bunch of Cree XP-Gs for a high speed flash - if used as a flash(+low powered modelling light) you can get away with a metal core PCB as a primary heat sink. That would be about 20klm of a 6x6cm area.Thermal management gets interesting once you want a video light.
But there you have to ask yourself: why concentrate the light in a small source you have to widen up anyways? Look at the Kino Flo products for inspiration and spread the LEDs. You avoid wasting about 3/4 of the light for starters...

Thank you for your reply. The fact that you've managed to make a working flash head out of LEDs is really encouraging. I'd be very interested to read more about it, have you posted any details/pics anywhere?
My apologies for asking loads of questions, but how did you get around the colour temperature/wavelength issues? I was discussing this with a videographer friend who works in commercial lighting supplies and is building his own video lights using strip LEDs (pretty much homemade Kino Flo's at a fraction of the cost) and he is using a combination of different temperature LEDs and dimmers to ballance his lights, but for a flash head I imagine the trial and error factor in getting this side of things right could prove costly.
Also, I was wondering what sort of sync speeds have you managed to achieve? I ask this as someone told me a while ago that it was the major problem with trying to strobe LEDs.
As regards the necessity to concentrate the light so much, I agree totally that it makes very little sense if you're using softboxes, brolleys, diffusers etc, and to this end I was thinking about converting some large patio heater ballasts I had lying around into constant LED lights, which would also be nice for the video people who use my studio (not to mention my electricity bill). However, for some of my other light modifiers, specifically snoots, beauty dishes (OK not insurmountable to achieve this effect with larger lights) and focussable spotlights, I'd still need to concentrate an awful lot of light into that small diameter.
I imagine the current technology is not all that far away from achieving this and it won't be all that long before the first LED studio strobes appear.

[jgbedford]

A friend of mine does a lot of Macro work, and wanted to try an LED ring light out... he gave the Sunpak unit a go and has had pretty good results with it.

http://www.bhphotovideo.com/c/search...283+4291178451

He had to set custom white balance to compensate for the LED colour temperature, but other than that - you can't beat the price!


JB

[precisionworks]

JB,

Thanks for mentioning the Sunpak ring light: http://news.cnet.com/8301-17938_105-10419568-1.html

I just ordered one from Amazon & can't wait to try it out. The ring light has an effective range from 2"-20", and that's the distance I work with for flashlight photos (especially trit images). It probably isn't what the OP is looking for as the Sunpak unit stays on all the time & is low output but it should be perfect for what I do.

[b18062a]

Hi all,

This forum was suggested to me by a respectable electronics guru, and I must say that I'm very impressed by the depth of knowledge here even with the small look I've had so far! This is my first post on the forum, so HI all

Without further ado, I've debated this idea myself for a very long time; especially as it means that if the head drops by accident, or dies, it's cheaper to fix. Led's are very powerful these days, and have endless benefits. My idea was to go all out custom, and build a fancy high-power led monohead. And, with a constant source of light, no triggers will be necessary. Colour will indeed be fun, but we'll see how that goes. Nothing like hands on testing!

For all those interested:

I recently went on Ebay and bought myself a 100w 6000lm led chip (warm white too, so it'll suit most natural light perfectly). I plan on mounting it to a large heat sink, custom cut to fit to my elinchrom soft boxes without damage. The thing is, the LED runs between 34-36v and so I need to buy or make an inverter (if anyone has ideas, let me know; as I’ve just started searching around). The plan is to MAKE one! So far, apart from having a car battery (which serves as an awesome weight I might add) to power the thing, and having bought the LED from china today, not much else is set in stone. I'll keep you updated as I go, and if anyone has any cool ideas in the meantime, please let me know. Any tips, circuits or suggestions are warmly welcome, and I'll continue perusing the forum in my spare time for anything nifty ideas that can help.

I'll keep you informed,
Julius

[blasterman]

LEDs' have a couple inherent issues when being used in place of strobes. The first is the intensity issue. You need a *lot* of LED wattage to match a typical camera strobe - even a low powered one. Next, Xenon strobes have near 100% CRI. Your typical cool-white LED doesn't. Some of this can be adjusted in post and some can't.

LED's work great for macro lights because the working distance is so close. They are also easy to make, and something you can throw together DIY is likely to be higher powered and have better color rendition than most commercial offerings. I recently went through B&H's LED offerings and it was laughable to say the least. Most are beehive lights, with a 3w unit costing $400

[b18062a]

Indeed blasterman, I wondered about the CRI myself until an interesting thought dawned on me, let me know what you think:

Typical CFL's are used all the time in the industry and have been for many years. Westcott is a big name here from my understanding. Lights of that variety use a UV light with a phosphor; ultimately producing the white (cold or warm) light needed. I can't comment on these lights, as I've never used them before, but it seems like a lot of pros manage to get by with them quite well; and they too are dimmer. LED's in the same way these days (also from my naïve understanding) work on the same principle. A UV led with phosphor creates the white light. When that dawned on me, I was like why not see how it goes, for $40 plus a little work, it's worth a try. I guess I'll see how the correction comes out. With the warm white, do you think there'll be more of a problem?

And like you said too, they are a lot dimmer. I don't know how much dimmer they would be in comparison to a 500w/s strobe at 1/1; probably a lot I imagine. That's another thing I wanted to find out. I guess they'd be similar to the guide numbers of fluro tubes in soft boxes right? 6000lm (at best) or even 4000lm with a poor chip driven at lower power at a meter away (without a soft box) is almost as bright as a dimmer projector globe isn't it?

And again, I completely agree with you comment on poor offerings at exorbitant prices. Give it a few years I think. LED's are jumping forward in leaps and bounds in recent years, we should start seeing something nice soon.

On the forum, I found a link to this guy. Looks like a simple enough setup to put together, which is great!
http://tesladownunder.com/WorldsBrightestBike.htm

And I think I found a great answer to all my problems, for all those that havn't seen this post, get into it I'll probably go down this path myself.
http://www.candlepowerforums.com/vb/...-Driver-for-12

If someone knows what to type into ebay to pull up similar boards to this, let me know

Julius

[AnAppleSnail]

I made a (approx 40W burst output) light here. The heatsink it sits on must be large for continuous operation at about 20W, but it could do bursts with just the copper slug. With burst operation you have to separate the heatsink from the heat rejectors. The copper slug is a heatsink - it holds heat by cooling the LEDs after, say, a 40W burst (Or 80W for about 180% power). The aluminum vanes then release the heat, which requires a fan when above about 10W average power. Running continuously at 20W it stays cool to the touch. 25% duty cycle at 80W would also stay this cool in a (2x3x2 inch) volume with the fan running.

I suggest mixing NW and WW color temperatures to help with color rendering somewhat. As for driving, I do not know. I would probably hack something with a sufficiently large battery and a switch.

[arek98]

The thing is, the LED runs between 34-36v and so I need to buy or make an inverter (if anyone has ideas, let me know; as I’ve just started searching around). The plan is to MAKE one!

HBFlex and Hyperboost are available very good drivers that will drive your LED at 100W. 6000lm at 100W is very low efficiency though.

[b18062a]

@ AnAppleSnail:

I'm still reading around here and learning, so in the meantime here are a few intrigues and questions:

1. That looks awesome! So I take it you have two 5W LEDs of each colour there? Do the colours render well in post? Any examples if it's not too much to ask? Have you tried only using a single colour, and do the limited wavelengths make that much of a difference?

2. Also, running them at 80W total, you state a guestimate reduced 25% duty cycle, but is that a realistic estimate? I've read around here that LEDs are ok with being over run for short periods, but what's your experience with longer running times at 40w? You said they stay cool, but have any run far shorter than lets say a 50% duty cycle? That's partly the reason for the 100 watter. That way I don't run it at it's full power, preserve the leds, and still get a decent duty cycle (that's the hope anyway). And, well, if I need the full power, it's there too :P

3. "With burst operation you have to separate the heat sink from the heat rejecters. The copper slug is a heat sink - it holds heat by cooling the LEDs after, say, a 40W burst (Or 80W for about 180% power). The aluminum vanes then release the heat, which requires a fan when above about 10W average power. Running continuously at 20W it stays cool to the touch."

When it comes to sinks, I wanted to know what was best for my LED in the long run, and I was amazed last night (and you might be interested to hear this too) to learn the following:


I tried a 1750 ohm resistor at 240v to get roughly a 35w output. The resistor had a special case such that it could be connected to a flat plate of a sink and cool nicely, thus testing the heat sink. I then tested two sinks in air without fans. After roughly 15min, a sink very similar to the one you've show got to 87C, where as a sink of the same size, just made with a thicker base, and far thicker and sparsely separated fins (like what you see on good old amplifiers), only got to 48C. I didn't measure the resistor on the first sink, but on the second, the resistor only got to 57C. All this with a room temp of 17C, and no fans to cool anything. Both stayed stable at those given temperatures after that +- a few degrees. I was blown away at how poor a sink the intel cooler really was; that or I'm really missing something here. Based on what you said in the quotation above, what's your opinion on these results?

@aarke98:

Thank you very much, I actually tracked those down through the forum yesterday too. The look way cool, and I was tempted; especially as they can supply so much, and have such small circuitry (or so it seemed). Funnily enough, and here is the kicker, I looked them up on the only Australian reseller, and they only rated them to 1300mA, which is why I didn't give them a second thought. You might be interested in seeing that for yourself:

http://www.cutter.com.au/search.php?...pe=&scat=&sman=

Instead, I opted for buying and editing a simple circuit, like the one in the last link in my previous post. I hope it does the job, we shall see I suppose.

Thanks for all the help and ideas everyone,
Julius

[AnAppleSnail]

Well, it's an aquarium light I made just before going on vacation. I run it at 20w, the LEDs are rated to 40w, and that limit is mostly thermal (can be overdriven). The XM-L line has been driven at 6A continuously, but there aren't many benefits to 6A over 4AI haven't taken pictures because I've been on vacation. It looks darn nice on an empty aquarium full of water. The sparse plants should love it. Maybe algae will too.Heat sinks with thin vanes are made for fans. I haven't tried this one fanless, but it must stabilize at some temperature... Hopefully an LED-safe one. That intel cooler is specced to reject about 100w heat... With a fan. Without, it's cooling by convection at a fraction of design airflow.Color: LEDs (white) produce decent color. Honestly, 85 CRI (cree typ. Cool white) is adequate, especially with a range of colors. I.made this for fish, so it's all cool white. If I went to take photos in tunnels, I would bring this beast and my high-cri, low-CCT flashlights to blend CCT in pleasant ways. LED spectrums usually miss greens and reds. This can be corrected; in PS you'll tweak the red and green saturation.

[blasterman]

Kind of curious why anybody would want to build an LED powered strobe......other than perhahps to do some low powered stroboscopic effects. Non dedicated Xenon flash units are pretty cheap and yet operate in the 100watt range. It's the dedicated ones with onboard logic that get pricey, but a basic camera flash is pretty cheap and there's no heat sink to lug around.

For continuous light HID is the most popular solution for high intensity, but the DIY projects here are certainly no slouch and can match or exceed the performance of 12volt HID. XM-L's are clearly the top end choice because of their low voltage / high current requirements and outstanding efficiency. Compared to most commercial LED based camera lights you are certainly better off going DIY.

[SemiMan]

I don't think anyone answered the lumen questions.

A 250 w-s strobe is likely in the 10,000,000 lumen range. Yes, that was the right number of zeros.

You can work back the math ... 250 watt-seconds (joules) in 0.001 second (or much less) and 40 - 50 lumens/watt

= 250 * 1000 * 40 = 10, 000, 000 lumens

Semiman

[blasterman]

And darn near 100CRI for the Xeon strobe.....

[strayz]

IF I may ask what are you doing to your likes that you are killing that many?

I have had my Elinchrom's for a few years and through thick and thin and on location and bounced around a lot. They are still working great, and take moderate abuse with out problems.