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DIY liteMat Plus 4.


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While I have down time I have been interested in making my own LiteMat plus 4. I can get led strips, Corrugated plastic sheets, and Velcro. I got all that down. 

But I need help if finding a power supply and bi color controller that will handle like 200w and not flicker at higher frame rates when dimmed. 

Anyone have experience with this? I know I can buy litemat power supplies and controllers but thats way to expensive for this project and at that point would just buy a litemat plus 4 defeating this whole exercise. 

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45 minutes ago, Alexander Sutton Hough said:

Not high enough wattage, not bi-color and his dimmer would cause flicker at higher fps and different shutter angles. Looking for something off the shelf but can handle that thoes requirements.

Sounds like you need to get the LiteGear parts then. ?

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21 minutes ago, Alexander Sutton Hough said:

Looking for something cheaper for DIY. There prices are to high for DIY projects. If I am going to spend that much I would just go the full way and buy a litemat plus. 

I'd be worried that going with a cheaper solution will just get you low CRI, crappy quality LEDs. Might be fine for your application, I've gotten away with some quite bad diodes in the past, but the reality is good LEDs are expensive.

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1 hour ago, Alexander Sutton Hough said:

Looking for something cheaper for DIY. There prices are to high for DIY projects. If I am going to spend that much I would just go the full way and buy a litemat plus. 

Honestly, the technical requirements you're hoping to meet are the reason why the LiteGear stuff is expensive; they've done the R&D to build something that meets those technical requirements.

Unless you've got a background in electrical engineering, meeting those requirements with cheap DIY solution will be difficult. That YouTube video I shared may not directly apply to your situation, but I believe it's a good starting point to finding a solution that works for you.

This guy built his with a dimmer switch that should work for frame rates under 1/1000:

Again, you're looking into a lot of R&D on your end. The amount of time you spend on this project can teach you a lot about LiteMats are made, which is super handy!

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The diy perks setup looks cumbersome and a bit flimsy

Yuji have high CRI mono and bi color strips, and high frequency dimmers

https://store.yujiintl.com/

Was planning on having a go at DIY-ing some 2x1 panels, using thermo-conductive epoxy to glue strips to aluminium plate, then encase it in diffusion silk and black ripstop fabric. Maybe with eyelets or velcro in the corners to assemble a larger panel out of several 2x1s.

A 200w panel would run for about $200-300.

Would love to hear from people who have made their own.

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I wouldn't recommend anyone use those PWM dimmers. You can create linear DC dimmers with a DC converter board and a potentiometer; it's not exactly the ends of invention.

Various people sell LED strip on ebay that's advertised as "high CRI." I have some of it here and having metered it, it's probably a good enough white light for general purpose use. I'd get a test length of whatever you're thinking about to ensure it's reasonable, and I'd buy all you need in one batch so at least your lights match among themselves. It won't match anything else but then not much does, which is one of the problems with LED lighting in general.

Bear in mind that the sticky strip is resistively ballasted so it is not as efficient as running bare LEDs with a current-limiting controller. That's also doable, but represents a small increase in what you need to understand.

It's hard to build bicolour controllers without a lot of screwing around. Better to just build a tungsten light and a daylight light in the same box, and have two controls so you can dial in what you want. Trying to build things with colour and brightness controls demands quite a lot more complexity, especially if you want it to be anything like accurate.

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The PWM dimmers I was looking at were in the 200Khz range, which is higher than HMI ballasts, and can take a lot of power. Plus not they're not overly expensive ($30-50) and have bi-color options. I'd stay clear of anything from amazon and ebay though.

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HMI ballasts working in flicker-free mode are often a lot lower than 200KHz, but HMI ballasts are not PWM devices. They do not leave gaps between the pulses in the two mutually-inverted square waves that drive the lamp, so the light output is so near to continuous that it tends to work quite well at a wide variety of frame rates. That's not true of PWM dimmers and they are likely to cause problems under at least some circumstances.

I think I'm doomed to spend the rest of my life explaining this to people, but you really should avoid PWM dimming for movie lights. It may sometimes appear to kind of work, a bit, under some circumstances. Sort of. It remains a bad idea.

You can do linear DC dimming for similar money.

P

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I found the power supplies litegear is using for for the 200w range for S2. As I suspected they use off the shelf Meanwell power supplies. The Plus series they have custom built. 

https://www.meanwell.com/webapp/product/search.aspx?prod=GST280A

https://www.litegear.com/product/power-supply-12v-dc-16-amp/

Now I just need a cheaper dimming option that reliable. 

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A lot of people use Meanwell. Fiilex, Cineo, I think Aputure have done. There's a lot of them, and the quality is very variable. Meanwell have good stuff (they also have terrible stuff.) There are many options. It's just a DC power supply. Most of the "LED drivers" that are advertised will be for commercial or domestic use and will use PWM dimming, but what you're looking at there is just a DC power supply.

The problem with LED strip is that, as I say, it's resistively ballasted. It's probably still more efficient than tungsten. 

P

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6 hours ago, Phil Rhodes said:

HMI ballasts working in flicker-free mode are often a lot lower than 200KHz, but HMI ballasts are not PWM devices. They do not leave gaps between the pulses in the two mutually-inverted square waves that drive the lamp, so the light output is so near to continuous that it tends to work quite well at a wide variety of frame rates. That's not true of PWM dimmers and they are likely to cause problems under at least some circumstances.

I think I'm doomed to spend the rest of my life explaining this to people, but you really should avoid PWM dimming for movie lights. It may sometimes appear to kind of work, a bit, under some circumstances. Sort of. It remains a bad idea.

You can do linear DC dimming for similar money.

P

Forward: I've built dozens of LED effects for movies and shows around the world, and recently released my own open source LED hardlight project--which, OP, if you're not stuck with the LiteMat form factor, I highly recommend you check out:https://github.com/MadlyFX/OpenLUX-LED-Video-Light

Your skepticism of PWM dimming is obviously well founded, as we've all been bitten by the negative effects it can have. However, the reality is that after about 15-20khz, PWM dimming is, for every "normal" circumstance, flicker free. Obviously everything has a gotcha, and if you're shooting high speed, or stupid high shutter speeds of course you'll see flicker. But if you're doing that, you are likely already looking into High Speed lights (and LEDs likely won't be bright enough.)

The issue with constant current dimming is that it affects the color and temperature accuracy of the LED. If you look at a white LED datasheet, they almost always have a graph showing an correlation of color shift vs Current. They are designed to driven at one voltage and one current for optimal performance, and deviating from that does, nearly always, have negative consequences. You're trading flicker for accuracy, essentially.

Lastly, since CC dimming circuitry needs to be able to "take the full brunt" of the current the LED is pulling, it may need it's own additional cooling and does take up more physical space. All these reasons are why even the big players often choose high frequency PWM dimming versus constant current dimming, it's essentially a choice of "make it 100% good in 5% of circumstances, or 90% good in 95% of circumstances.

(Also you mention dimming LEDs with a DC converter board, which you can do, but just to clarify for OP, you want one that allows you to control the current, not just the voltage. Unlike Tungsten, LEDs are constant current devices, the voltage fluctuates to maintain the rated amperage.)

Also found this really great article: https://www.powerelectronics.com/markets/lighting/article/21861301/how-to-add-analog-dimming-to-virtually-any-led-driver

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16 hours ago, Andy Jarosz said:

Forward: I've built dozens of LED effects for movies and shows around the world, and recently released my own open source LED hardlight project--which, OP, if you're not stuck with the LiteMat form factor, I highly recommend you check out:https://github.com/MadlyFX/OpenLUX-LED-Video-Light

Your skepticism of PWM dimming is obviously well founded, as we've all been bitten by the negative effects it can have. However, the reality is that after about 15-20khz, PWM dimming is, for every "normal" circumstance, flicker free. Obviously everything has a gotcha, and if you're shooting high speed, or stupid high shutter speeds of course you'll see flicker. But if you're doing that, you are likely already looking into High Speed lights (and LEDs likely won't be bright enough.)

The issue with constant current dimming is that it affects the color and temperature accuracy of the LED. If you look at a white LED datasheet, they almost always have a graph showing an correlation of color shift vs Current. They are designed to driven at one voltage and one current for optimal performance, and deviating from that does, nearly always, have negative consequences. You're trading flicker for accuracy, essentially.

Lastly, since CC dimming circuitry needs to be able to "take the full brunt" of the current the LED is pulling, it may need it's own additional cooling and does take up more physical space. All these reasons are why even the big players often choose high frequency PWM dimming versus constant current dimming, it's essentially a choice of "make it 100% good in 5% of circumstances, or 90% good in 95% of circumstances.

(Also you mention dimming LEDs with a DC converter board, which you can do, but just to clarify for OP, you want one that allows you to control the current, not just the voltage. Unlike Tungsten, LEDs are constant current devices, the voltage fluctuates to maintain the rated amperage.)

Also found this really great article: https://www.powerelectronics.com/markets/lighting/article/21861301/how-to-add-analog-dimming-to-virtually-any-led-driver

Well done on getting an open source project out there; it's something I'd repeatedly intended to do but never got around to.

Next, colour mixing. I might know someone who could help with that, if you felt like a collaborator.

Re PWM my concerns linger. Driving a large (multi-amp) load with 15-20KHz PWM is likely to create truly majestic amounts of RFI at audio-relevant frequencies, unless it's rise-time limited, in which case the problem becomes one of overheating the transistors. You can LC filter it but then you've basically built a DC converter by the back door. Possibly you could get away with building one in the shed, but nobody's ever going to be able to get a product that does that through compliance testing in any responsible jurisdiction (in China it's fine, apparently.) Nobody likes a buzzing noise, and in any case PWM at almost any frequency can create venetian blinds on rolling shutter cameras. I take your point that it can sometimes work, but I'm not comfortable recommending it as an approach.

I keep looking around for a low-cost DC converter with digital control - I suspect it's obvious why, but there aren't many of them. I found a couple with serial control but the response time was lousy; hundreds of milliseconds, which made fades clunky.

P

 

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18 hours ago, Phil Rhodes said:

Well done on getting an open source project out there; it's something I'd repeatedly intended to do but never got around to.

Next, colour mixing. I might know someone who could help with that, if you felt like a collaborator.

Re PWM my concerns linger. Driving a large (multi-amp) load with 15-20KHz PWM is likely to create truly majestic amounts of RFI at audio-relevant frequencies, unless it's rise-time limited, in which case the problem becomes one of overheating the transistors. You can LC filter it but then you've basically built a DC converter by the back door. Possibly you could get away with building one in the shed, but nobody's ever going to be able to get a product that does that through compliance testing in any responsible jurisdiction (in China it's fine, apparently.) Nobody likes a buzzing noise, and in any case PWM at almost any frequency can create venetian blinds on rolling shutter cameras. I take your point that it can sometimes work, but I'm not comfortable recommending it as an approach.

I keep looking around for a low-cost DC converter with digital control - I suspect it's obvious why, but there aren't many of them. I found a couple with serial control but the response time was lousy; hundreds of milliseconds, which made fades clunky.

P

 

My little open source light pulls up to 6 amps and runs at 10Khz, absolutely nothing even close to audible whine. Remember that a lot of these driver modules and ICs have to be vetted in and of themselves, for example attached is the testing for the driver I chose. I haven't actually read any of these certs, I have no idea what they mean, but it's a far cry from "not being able to get through compliance testing." It's absolutely possible, and most of the fixtures you use on set on a daily basis have done it. Skypanels, LED Lekos, etc. are all PWM. Fan noise will most certainly be louder and broader spectrum than any whine.

Using a filter is a fine solution and actually can work well, but it limits the max brightness of course.

Another thing to consider is remote phosphor fixtures like the Cineos can use the phosphor itself to add some "photonic inertia" that smooths out the flicker. I've even seen this with regular diffusion at high frequencies.

And yeah, RGB mixing is definitely on my radar--but I'm wanting to wait until I have regular access to a colorimeter, as the fun part for me is figuring out the right mixing algorithm to look correct to the human eye.

 

 

Screenshot (112).png

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I was thinking rather of RFI, radio-frequency stuff. And there's some high speed footage around somewhere of a phosphor-converted LED being pulse width modulated; you can actually see the blue light come on before the phosphor wakes up, and the reverse when it goes out. It was actually being explored as a way of making colour-tuneable LEDs without needing two junctions. The grim reality is that nothing is simple or easy.

And I really, really wouldn't take skypanel as an engineering keynote on this!

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  • 1 year later...
On 5/5/2020 at 9:32 AM, Alexander Sutton Hough said:

While I have down time I have been interested in making my own LiteMat plus 4. I can get led strips, Corrugated plastic sheets, and Velcro. I got all that down. 

But I need help if finding a power supply and bi color controller that will handle like 200w and not flicker at higher frame rates when dimmed. 

Anyone have experience with this? I know I can buy litemat power supplies and controllers but thats way to expensive for this project and at that point would just buy a litemat plus 4 defeating this whole exercise. 

Just buy a LiteMat hahahaha 

When you account for the fact that TIME IS MONEY, you'll save by buying it and having the warranty coverage and technical support.

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