Jump to content


Photo

LED Flicker


  • Please log in to reply
11 replies to this topic

#1 Dave Kovacs

Dave Kovacs
  • Basic Members
  • PipPip
  • 21 posts
  • Cinematographer

Posted 21 December 2010 - 05:28 PM

I have seen Chinese LED panels on EBAY that have 600-piece-LED arrays, similar to other brands with American names.
I'd like to know if anyone here has used any of these foreign brand LED panels? Do they have flicker issues?
  • 0

#2 John Sprung

John Sprung
  • Sustaining Members
  • 4635 posts
  • Other

Posted 21 December 2010 - 06:13 PM

Flicker characteristics could be specific to each make and model, and even vary from unit to unit. If they're not designed for film/video use, it's a crap shoot.





-- J.S.
  • 0

#3 Tim Tyler

Tim Tyler

    Administrator

  • Admin
  • PipPipPipPip
  • 1291 posts
  • Cinematographer
  • Olympia, WA (US)

Posted 21 December 2010 - 07:45 PM

I know a guy who bought two ePhoto 500 LED Ultra Bright things and he said they were a good value. I think he got them from Amazon, not eBay. The ePhoto lights replaced some other cheap LED's he bought then returned which advertised 56k with a high CRI but in fact looked nothing like daylight.

FYI: My experience with production equipment has taught me that you get what you pay for. Quality, familiar brand movie lights hold their value and usually last longer than knock-offs too.
  • 0

#4 Patrick Neary

Patrick Neary
  • Basic Members
  • PipPipPipPip
  • 873 posts
  • Cinematographer
  • Portland, OR

Posted 21 December 2010 - 08:00 PM

Hi-

I've been using 2 FloLight panels for the last year and they are great- rugged and very versatile.

I also carry a bunch of those little white rechargeable "home security" led lights from Costco ($20 for 2-pack) and other than a slight green spike they are also great. Stick a piece of velcro on the back and you can put them anywhere, they are quite bright and have two power level settings and last forever on a charge.

A friend has a couple lowell blenders and sorry to say those things are awful. Cheaply made, flicker like crazy every time I've tried to use them, and the battery holder is a disaster. A good idea not well executed.
  • 0

#5 Mathew Rudenberg

Mathew Rudenberg
  • Basic Members
  • PipPipPipPip
  • 252 posts
  • Cinematographer

Posted 21 December 2010 - 11:58 PM

I finished a shoot recently where Art Dept would occasionally mix LED christmas lights in with the old school ones.

It was pretty easy to tell the difference - the LED's flickered and we couldn't find a shutter angle that would eliminate that flicker.

I did, however. find that it was only the plug in (AC) LEDs that flickered, the battery powered LEDs we had on set did not. I suspect this is due to the sine wave cycle of the AC power/ not having a great transformer on cheap christmas lights, however I didn't take the time to test them or anything, we just stopped using the LED models.
  • 0

#6 Dave Kovacs

Dave Kovacs
  • Basic Members
  • PipPip
  • 21 posts
  • Cinematographer

Posted 22 December 2010 - 09:47 AM

Tim,John- You're right, you get what you pay for. Dp'ing alot of low budget stuuf, I've learned which corners to cut and which one not to cut.

Patrick, Matthew- Thanks for the tip. I'll go by Costco and pickup some of those small fixtures. Last week, I watched a
mid-level budget film with B-list actors that had a scene where an actress enters her dark apartment. The room was illuminated by one of the LED wire scupture reindeers. It was flickering like crazy!!! I'm thinking ' somebody did not test cheap LED reindeer lamp'.

I read this article about the EPA and the switch from the 120hz standard to 150hz, and now back to 120hz.
http://www.optoiq.co..._about_led.html

Perhaps this may have added to the problems with flicker.
  • 0

#7 JD Hartman

JD Hartman
  • Basic Members
  • PipPipPipPip
  • 1690 posts
  • Gaffer
  • Edison, N.J. U.S.A.

Posted 22 December 2010 - 10:31 AM

"A friend has a couple lowell blenders and sorry to say those things are awful. Cheaply made, flicker like crazy every time I've tried to use them, and the battery holder is a disaster. A good idea not well executed. ", not at all surprising, considering the source.

Flicker on the cheaper LED panels and holiday lights would come from poor filtering in the power supply (AC ripple). If you've any electronics experience, this may be eliminated with additional filtering capacitors and or a filter choke in the power supply (if it's a traditional linear supply).
  • 0

#8 John Sprung

John Sprung
  • Sustaining Members
  • 4635 posts
  • Other

Posted 22 December 2010 - 02:00 PM

The KISS method of powering LED's would be to throw a bridge rectifier across the incoming 60 Hz AC, giving you 120 Hz pulsed DC. The suggestion of going to 150 Hz betrays ignorance of the fundamentals.




-- J.S.
  • 0

#9 Dave Kovacs

Dave Kovacs
  • Basic Members
  • PipPip
  • 21 posts
  • Cinematographer

Posted 22 December 2010 - 04:36 PM

The KISS method of powering LED's would be to throw a bridge rectifier across the incoming 60 Hz AC, giving you 120 Hz pulsed DC. The suggestion of going to 150 Hz betrays ignorance of the fundamentals.




-- J.S.


Can that type of modification be done with a soldering gun, or this beyond the 'I got my gear from Radio Shack' skill set?
  • 0

#10 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11934 posts
  • Other

Posted 22 December 2010 - 05:35 PM

It's not the end of the world as tasks go, but you don't want to mess with mains if you're in any way unsure.
  • 0

#11 John Sprung

John Sprung
  • Sustaining Members
  • 4635 posts
  • Other

Posted 22 December 2010 - 05:45 PM

It's well within the Radio Shlock skill set -- but you get better prices and selection from Digi-Key:

http://www.digikey.com/

http://ordering.digi...WT.z_lt=60-Watt Light Bulb using LEDs&WT.z_ref_page_id=lighting_hp&WT.z_video_source=TZ Lighting



-- J.S.
  • 0

#12 Hal Smith

Hal Smith
  • Sustaining Members
  • 2280 posts
  • Cinematographer
  • OKC area

Posted 23 December 2010 - 12:03 AM

LED at the most basic level are a rectifier, feed one with AC and you'll get pulsations. The only way to avoid this is indeed to feed them with DC, either from a battery pack or a well filtered source of rectified AC. I'd start with a industrial "brick" power supply, they're cheap on eBay. The transformer types are more reliable in rough service but they are quite a bit heavier than chopper (inverter) supplies.
  • 0


Rig Wheels Passport

The Slider

Broadcast Solutions Inc

Media Blackout - Custom Cables and AKS

Paralinx LLC

Opal

Ritter Battery

Metropolis Post

Glidecam

Visual Products

rebotnix Technologies

CineLab

Wooden Camera

Abel Cine

Tai Audio

Aerial Filmworks

Technodolly

FJS International, LLC

CineTape

Gamma Ray Digital Inc

Willys Widgets

Paralinx LLC

Abel Cine

rebotnix Technologies

Metropolis Post

Willys Widgets

The Slider

CineLab

Tai Audio

Rig Wheels Passport

Visual Products

FJS International, LLC

Gamma Ray Digital Inc

Technodolly

Wooden Camera

Media Blackout - Custom Cables and AKS

Aerial Filmworks

Ritter Battery

Glidecam

CineTape

Broadcast Solutions Inc

Opal