Lighting for Practical Light Sources - How to stop flicker

Hi there,

I've been doing a bit a research and am surprised to have found very little on this so far but I was wondering if anyone had some recommendations for lighting practicals.

I bought a strip of small LED lights and whenever I have tried to use them, I get a noticeable flicker from frame to frame. I tried taking longer exposure and I'm still seeing the flicker.

I found that the strip is actually too big to be useful in small things like lamp shades and because they need to be plugged in. Even without the flicker they might not have been too useful. 

I've started reading about 'full wave' or rectified LEDs - do these really reduce the flicker? I spoke to a friend who had used a strip of LEDs but had diffusion over them, I don't see how that would change my situation much but I'll give that a try.

If anyone has any practical lighting tips (even dollhouse esque shop centers that sell working practicals), I'd love all the input I can get.

I'm looking for lit lamps, a refrigerator light, and a small light that I can stick in a fish tank. 

Thanks!

Savannah

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I've used old 12 volt incandescent globes (used in old style indicator lights, usually with a red, green or amber plastic cover on them, for electronic equipment)  with a transformer.  Tiny little things, grain of rice size some of them.   And some LEDs which have no doubt replaced them by now.  The incandescents got very hot and often I had to switch them on, take the shot, and switch them off again, before my prop melted.   LEDs are better.   All are fine if the power is steady.

I get flicker with most of my lighting because the 220-240v AC electrical power is not completely steady, it goes up and down by a volt or two.  A factory a block away, turning on a big machine, or my own oven in the studio, can make the voltage drop.  Any light that can be controlled by a dimmer will get brighter or dimmer when the voltage changes.  With animation, this comes across as a sudden change.  I had to invest in a power conditioner.  First I tested with a multimeter attached to the mains power that ran the lights, and put it in front of my camera.  I could see that on the brighter frames, the needle went up, so it was the power doing it.  (It happened over a couple of minutes,  and could stay high or low for half an hour before changing again, so long exposures wouldn't fix it.) I was afraid that after all my trouble getting manual lenses and making the lens aperture stay stopped down all the time, my camera had somehow developed flicker, but in fact it was accurately recording what the lights were doing.  My Double Conversion UPS from Eaton Powerware fixes it by taking in the 240v AC, converting to 12v DC and charging a battery, drawing power from that, and converting back to AC.  It drops a couple of volts but stays steady.  A portable one could set you back around $1500, so not cheap.  A regular UPS is no good, it doesn't smooth the power, it's job is to kick in with battery power if the mains power cuts out completely, so not the same thing.

I don't know anything about rectified LEDs - worth reading about.

I tried a string of LED christmas lights that run on mains power.  Worked fine as a row of lights on a cinema marquee, but when I thought I could run just one on the same power, it blew up!  Obviously the power is distributed across all of them.   But I could run one with a cheap transformer that can be set to 3v, 4.5v, 6v, or 12v.  I think 4.5 worked.  Again, with filtered power, it didn't flicker. 



StopmoNick said:

My Double Conversion UPS from Eaton Powerware

Do you happen to have the model number? I'm looking into these for when I go back to NZ and start my new studio up.

Thanks!

EDIT: nevermind, I think I found them. "Double conversion UPS" was the search term I've been after for many years :D, thanks again Nick.

I discovered the main culprit causing flicker in my house was the heater kicking on. I had to adjust the thermostat so it wouldn't come on until the shot was done, so I was getting colder and colder throughout the shoot, but my lighting remained steady. Though it's possible a neighbor's heater might have the same effect, and I can't very well ask them to switch off their furnaces for the next few hours.. 

I have used the dollhouse lighting and it works well. I like the fact that you get a complete system  - transformer you plug into the wall, lots of wiring, little connectors so you can connect several wires branching off from your main one to different lights, and then the bulbs themselves. They have grain of rice and grain of wheat bulbs (which are a little bigger) that come in various basic tints (red green and amber I believe as well as clear) or you can scribble on the glass with magic markers to tint them. Might be able to use some kinds of paint too, not sure. I just bought a beginner's kit which included everything I needed, plus I got a bundle of extra bulbs. There's an instruction book on how to set everything up and little tools. Oh, I would stay away from what they call tape wiring and use 'round wire' - the tape is essentially a flat metal strip that you install under the base of the dollhouse (or in my case around the edge of my animation table) instead of using standard insulated wire (round wire as they call it). Seems like more of a hassle, though I didn't try that. To me the round wire just seems more intuitive. 

Hendrikus,

Model numbers would have changed by now, it was 6 years ago.  And I bought a bigger 5000 VA unit that wires into the mains power, because I had already put a lighting circuit in with sockets on the ceiling so I could hang my lights on 50mm pipe and plug them in up there.  However, the agent for Eaton here did loan me a smaller 1500 VA plug-in unit to test for a few days, so I could see if that would solve my problem.  With today's lower energy lighting, the smaller unit would have been more than enough. And less noisy, the big one makes a buzzing noise that really annoys me, but the small one just had a slight fan noise like a computer.   So I recommend  the plug-in 1500 VA models.   They seem to start as small as 700 VA, which does not run 700 watts at 240v, it's a bit less, I think there is a formula for working it out. 

My supplier in Australia was NPS.  It doesn't look like they operate in NZ.  http://www.nps.com.au/?s=double+conversion+ups

Originally I sent an email inquiry to Eaton in the US via their website, and they emailed me with the contact number for NPS in Melbourne.  Eaton might have a distributor in NZ as well.

For colouring lightbulbs, there is something called Stain Glass Paint that you might find at an art supply shop.

If you are wiring the LEDs yourself (rather than pre-wired connections) the wiring itself may be the problem. I recently worked on a small Arduino controlled LED setup which initially had some flicker and found that the mains voltage variance wasn't much of an issue but that some botched wiring between the LEDs, the busbar, and controller was causing enough voltage drain within the circuit to produce flicker.

Prewired strips with proper connectors shouldn't generate much flicker on their own, so in that case unsteady AC voltage is likely to blame. However, if your main lights for the rest of the set (not the practical LEDs) aren't exhibiting any flicker I'd be inclined to think it's a problem specific to your current LED setup.

I was talking to a friend who is an engineer, and apparently, LED pulses to create light. It pulses in a way that we perceive LED as 'solid' light. It has something to do with how the LED light waves are being emitted. And if you were to dim LED lights, they actually pulse slower. 

I'm not sure if this contributes to the fact of the flicker, but I thought it was quite interesting on how LED emits light.

Hopefully this helps
:)

 

That's not quite true.  LEDs do not inherently pulse, if hooked up to a DC power supply (like a battery).  However, if they're supplied with AC power (e.g. plugged into the wall), then they will reflect the characteristics of the power signal they're receiving.  Like all diodes, LEDs are one way streets for electric current, so if fed a raw AC signal, they'll only light up half the time (half-wave); I assume the "full wave" LEDs Savannah was looking at have circuitry to change the power signal applied to the LEDs to keep current flow in one direction, but unless there's a capacitor or something to smooth out that signal, the magnitude of the signal will still fluctuate, resulting in LED flicker.  But it's still driven by the power signal applied to the LED rather than any inherent properties of the LED itself -- with a constant DC power supply, LEDs do not pulse.  I've used battery-powered LEDs as practical fixtures, and the only problems I had could have been fixed with larger batteries.

All that being said, as others mention above, visible flicker in an animated sequence isn't likely to be from a high frequency, consistent flicker like LEDs on AC would have (unless you're shooting with a really fast shutter speed).

ChinAnn Teh said:

I was talking to a friend who is an engineer, and apparently, LED pulses to create light. It pulses in a way that we perceive LED as 'solid' light. It has something to do with how the LED light waves are being emitted. And if you were to dim LED lights, they actually pulse slower. 

I'm not sure if this contributes to the fact of the flicker, but I thought it was quite interesting on how LED emits light.

Hopefully this helps
:)

 

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