Flicker-Free Lights, and Why They are Important to You


If you only shoot outside, using the sun and reflectors for light sources, it is highly unlikely that you will encounter flicker problems. However, for the rest of us, flickering light sources can become a daily headache when shooting video. What is important to remember is that most electrically generated light sources flicker in some manner, but what matters is how perceivable that flicker is when we are shooting. I can hear you thinking: “Wait, that’s not true—tungsten lights don’t flicker and neither do LED lights, because they are DC powered.” Now, while that may be true for many applications, it is not always the case. Read on to see how to avoid having flicker ruin your day.

Under normal conditions, tungsten bulbs don’t flicker on video, but there are times they will and here is why. When plugged into an AC power source, the bulb’s filament is heating up 60 times a second, and cooling down 60 times a second (in the US). As the filament heats up, it starts to glow and emit light, and when the power is off, the filament glows even as it is cooling down—until the next cycle starts and the filament glows again. Now, all this happens too quickly for the human eye to see, and during normal shooting frame rates, the camera is capturing the same number of light pulses on each frame, so the flicker isn’t noticeable. As you increase the camera’s frame rates, or run off speed, you end up with frames that don’t have a consistent number of light pulses per frame, and these frames will exhibit flicker. This is most noticeable with smaller-wattage bulbs; once you get to a 5,000-watt bulb the filament gets so hot that it doesn’t cool enough in between cycles to flicker. You could use DC voltage to power your lights; this way, the bulb never goes through an on/off cycle, but finding 120 volts of DC isn’t as easy as it was around the turn of the 20th Century.

At this point you may be thinking, “I don’t shoot high speed (above 100/120 fps), and I’m using fluorescent lights anyway, and these don’t flicker.” If you are thinking this way, then you may be surprised to find out that flicker can be even worse with standard fluorescent lights than with tungsten lights, and that is even before you start dimming. For many years, in the US, the common setup for shooting under fluorescent lights was to use a 180-degree shutter and shoot at 24 or 30 fps. Nonetheless, with the increasing number of digital cameras offering shutter angle control and multiple frame-rate settings, shooting under fluorescent lights that are flicker free becomes very advantageous.

The light from a fluorescent bulb is generated by an arc, running through the tube, creating a plasma inside the tube that excites the phosphor coating on the inside of the bulb. The phosphors glow, releasing the visible light we see. A standard US household fluorescent light turns completely on and off 120 times a second—60 on, and 60 off, which is too fast for us to notice consciously, but this is not always the case with a film or video camera. In the US, for example, the household frequency is 60 Hz, and if you are shooting with a camera running at 30 fps, then that will give you two pulses of light per frame, no matter where in the cycle you start or stop the camera. This will remain consistent and not vary during the shot, so there is no noticeable flicker. This is, of course, all theoretical because in reality your camera is probably running at either 29.97 or 59.94 frames/fields per second (and not a true 30 or 60), which makes it easier to use your footage in a broadcast environment. Cameras that shoot at 24 fps can suffer from this, as well; unless you’re shooting a true 24p, your camera may be running at 23.976. How much of a problem is this under normal circumstances? It’s probably not a huge problem, although I have seen lots of color shifting going on when shooting under standard household fluorescent lights. This is something you definitely want to avoid.

What is ballast? 
The ballast is built into a fluorescent light fixture and takes the common household 120 volts, then generates the high voltage necessary to create the arc. After generating the arc, the ballast controls the flicker rate of the fixture.

However, if you are shooting at variable frame rates, or high speed, especially at frame rates that don’t easily divide into 60 (in the US) you are likely going to encounter flicker problems. To avoid this, you want to stay away from using household fluorescent fixtures, because they usually have very inexpensive ballasts, which have a very low flicker rate. You want to use “Flicker-Free” fixtures, which flicker at up to 250,000 times a second (250,000 Hz), such as Kino Flo or, if you are trying to light your scene using practical bulbs, you can try Lowel compact fluorescent bulbs, which fit into standard US household light sockets but have a flicker rate of 20,000 Hz, so they are significantly less likely to flicker than regular household fluorescents—but they are not as flicker free as Kino’s or other lights that use high-frequency ballasts.

This brings us to LED lighting, which can be powered by either Alternating Current (AC), or Direct Current (DC). LEDs that are powered by AC power supplies that step-down household voltage to levels appropriate for LED lights will exhibit similar frame-rate flicker issues as fluorescent lights. Most, if not all, LED light fixtures for video production are DC powered, either through a coax power input or batteries, which would seem to make these units flicker free. However, when powering an LED light from an AC outlet using an AC/DC power supply, you may run into a problem. A poorly made power supply can allow some AC voltage to pass into the LED light, creating what is referred to as “ripple.” This AC ripple can cause the LED fixture to pulse or flicker, affecting your shot. Using a battery can alleviate this problem, as the battery provides DC and DC only.

What is a Practical?
A practical is any light source such as a candle or flashlight; or a light fixture such as a desk or floor lamp that is in the frame and provides or appears to provide the light source for the shot.

Another consideration, when working with LED lights, is dimming. Dimming a light can cause problems across tungsten, fluorescent, and LED lighting. Dimming a tungsten bulb (household or professional) can lead to the bulb’s filament vibrating or “singing,” creating a problem for the sound recordist. With fluorescent bulbs, depending on how the bulb is being dimmed, you can end up destabilizing the arc, causing it to wander or pulse, creating a very obvious flicker. Some fluorescent lights have a limit (often 10%), as to how dim you can make them without flickering, so don’t assume a flicker-free light remains flicker free from maximum brightness to off (100 to 0%). LED lights can also suffer from flickering when dimmed, even if you power your LED light with batteries.

Dimming an LED light is often accomplished using a method known as Pulse Width Modulation, which works by cutting the power to the LED, essentially introducing off periods to the LED. This causes the light to be less bright over time by pulsing the LED. If the pulses happen rapidly enough, they are undetectable to the human eye and camera. Nonetheless, as with fluorescent lights, you now have a light source that is flickering. If the pulses don’t align with your frame rate, then your footage can show flickering, even if it is not noticeable to your eye. There is another form of dimming technology, referred to as Switch Mode Regulation, which operates at 500,000 Hz and is flicker free at virtually any frame rate.

So remember, when choosing your lighting, be it tungsten, fluorescent, or LED—most of the time, whether or not your lighting is truly flicker free or not probably won’t make a difference. But if you are shooting non-standard frame rates,  high-speed video, or dimming your lights, then using truly flicker-free lighting units may just save you from an unhappy surprise.


"When plugged into an AC power source, the bulb’s filament is heating up 60 times a second, and cooling down 60 times a second (in the US)"... This is completely incorrect. The filament is heating up and cooling down 120 times per second for 60Hz, since the electrons flow both ways through the filament, therefore there are 2 points for every cycle that the voltage is 0 and 2 points that the voltage is 220V (220-240 depending on location in world). 1 herz: 0V, +220V, 0V, -220V, 0V
(In the case of LEDs this would be 60 times a second if connected directly to AC as a diode only allows current one way, but LEDs are connected to rectifiers to switch the direction of the current, AC-DC converter. That means these also have 120 phases/flickers per second.)
Please update the article.
Source: BSc Physics.

I plan to shoot with 120fps in an indoor studio setup in India(AC power is 220-240V and 50hz)

Would it be better for my to use kino flo connected to AC or would it be better for me to use led strips connected to DC.


According to Kino Flo's website, they state the following:

"Kino Flo ballasts can operate at 50Hz, 60Hz and as high as 400Hz. When shooting in a 50Hz country, it will be important to use a 230VAC ballast or use a step down transformer. The Kino Flo ballast is designed to be flicker-free in either a 50Hz or 60Hz environment.  Kino Flo ballasts are designed to be flicker-free at any shutter speed or shutter angle on film cameras. Depending on the model, Kino Flo ballasts operate between 25kHz and 48kHz essentially eliminating flicker. However, there is mounting evidence that electronic cameras display different image capture methodologies that may result in flicker from gas discharge sources and surprisingly even quartz lighting. With electronic cameras the flicker becomes evident at the time of capture. If flicker is observed, then it is essential to shoot within the standard flicker-free speed and shutter angle settings. It is always best to run a test prior to your shoot date."

Both Kino Flo lights or battery-powered LED lights should work for stated usage needs.  However, as with all items we carry, I recommend testing your setup at the camera settings you will be using and at the power output levels you need before your shoot.

It says "Direct Current (AC) ", in the article, just a small typo..

I have cast out the "A" and replaced it with a "D." Thank you for your eagle-eyed attention. I read all the copy on this website by myself, so an occasional errant letter slips through. — Copy Editor

Just to clarity, are all light buts flicker or only, fluorescent, LED? I've encountered several articles the provide correlation between flickering lights and health problems (headaches, difficulty with concentration). Is there a practical way of assessing which light bulb is flicker free for day to day use? Is the electromagnetic interference most highly generated by fluorescent bulbs correlate with the flicker rate? How to assess LCD display flicker rate easily?


Thank you

Hi Stan -

Fluorescent lighting tends to produce the most flicker.  We are addressing only lighting for photo and video use.  We are not prepared to discuss environmental lighting or any EMF issues generated by household or commercial space lighting.

Please contact us via e-mail if you have additional questions:  [email protected]

Hold up a small solar panel attached to headphones....You will hear the flicker...

Thank you, now I know why my video shoot at a community center with a lot of florescent lights had such horrible banding effects. But... I can't change the lighting there. In the real world how do I take video? I made it worse by shooting at 59.94 frames/fields per second, yes, but what should I use instead (and still have it be as high res as possible)?

Also, there was a slide show going on and everytime it changed from a very dark slide to a light slide with lots of text there was a crazy bokeh effect going on so badly you could read any text until I zoomed in and out and then it went away. So strange! I'm using a Panasonic HC-V720. Any suggestions really appreciated.

Generally with floursecent lights they work on a specturm that causes these banding issues, so what shooters do is adjust their shutter to match that of the flourescent lights.  See the following link for some helpful tips on how to set your shutter up to match the frequencies.  http://urbanvideo.ca/avoid-video-flicker. There is a chart there but  it depends on the lighting that is used in your community center.  You may wish to do some test shots there prior to your next event.

In regards to your slide show issue, the transition from bright to dark between slides is causing an issue with the autofocus.  You're camera has a manual focus capability.  Preseting the focus on it manually and disabling the AF should solve that problem.


Sometimes it's just a matter of how the editing program processes the footage. I know I've had problems when shooting where the footage was flickery when there was no issue with the lighting. Even with this video I shot, http://thirdbornentertainment.com/timelapse-hyperlapse/ there is some flicker but is all due to post processing. 

Not everybody wants flicker-free light.

In one machine shop I know about, all of the lathes and mills have stroboscopic markings for setting the speed of the tool. They relied on the flicker of the fluorescent lamps that used to be there. Then the physical plant replaced all of the light fistures in the machine shop with new electronic ballast T-8 lamps. Now the strobe markings don't work anymore. Worse, they can't find any new fixtures that will give them the flicker they need to set the speeds.

When plugged into an AC power source, the bulb’s filament is heating up 120 times a second, and cooling down 120 times a second (in the US). A bulb works on both the "positive" rise and the "negative" rise of ac power.

Anonymous wrote:

When plugged into an AC power source, the bulb’s filament is heating up 120 times a second, and cooling down 120 times a second (in the US). A bulb works on both the "positive" rise and the "negative" rise of ac power.

Sorry, but this is incorrect. Like the article states, alternating current in the U.S. cycles at 60 times per second or 60 Hz (hertz), has nothing to do with the voltage (120V)

Wrong. In the US, alternating current cycles at 60 Hertz, but there are 120 half cycles. Think of a sine wave. You have the first half of the wave above the 0 volts line, and the second half below it. Those are your 2 half cycles. Each time the wave crosses the 0 volts line the polarity changes direction, which in turn means that the bulbs filiment would be heating and cooling. That happens 120 times per second.

This is an awesome article, and helps one to justify (and understand) the higher pricing being asked for some of the professional video lights out there.  A tip of the hat to the author for the knowledge that has been conveyed here.

Nice article.

Looks like the typist had a little flicker on the first line, last word of the paragraph beginning with "This brings us to...". :-)

Excelente artículo sobre el fenómeno de flicker en el sistema de iluminación. Este es un buen medio para capacitarse en los diferentes aspectos de la tecnología concerniente este rubro.