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Understanding PAL (50HZ) and NTSC (60HZ)

When filming you may have noticed that your LED lights are flickering on the camera, although this might not be the case in reality when looked through the human eye. Everything might seem normal to your eyes but not to when seen through the camera.

This can present a whole level of a nightmare when using LED lights in the film industry. This can be attributed to something referred to as LED refresh rate commonly known as Pal (50hz) and NTSC (60 Hz). The 50 Hertz stands for on/off 50 times a second and 60 hertz is on/off 60 times a second

We will be highlighting a scenario we encountered and providing with solutions to this problem.

We recently took on a job for a documentary which was to be shown in China. We were to work on the project from Canada and send this to China once we were done. Our shooting specification was 1080i50 in a .mov wrapper. This may seem super easy, after all, we should have just switched the camera settings to suit PAL from and we would have been good to go.

This is, however, is not as black and white as it may seem. The simple reason, our shooting is targeted for PAL though this is happening a location that is NTSC. This is one of the reasons why it is of paramount importance to discuss the standards that underlie NTSC and PAL. The NTSC and PAL standards might look the same to some people before they have a good understanding of what they are about. That said, we decided to explain why the two are different, what better way than to explain where this all began?

50HZ versus 60HZ, What is the history behind the two?

In places such as the UK, the majority of Asia, Russia and Africa, the AC current that supplies our electrical mains usually runs at 50 hertz (Hz). On the other hand, North America as well as a couple more countries uses the frequency 60Hz. Japan uses both 50 and 60Hz.

There are different factors that can be associated with this particular difference though economics play a huge role. The beginning of the 21st century saw manufacturers competing against each other, to differentiate themselves and position themselves as a monopoly, manufacturers based in the United Kingdom concentrated on production of 50Hz equipment while those in America produced 60Hz.  

These two frequencies are not in any way random frequencies, the two have grown in popularity over time. There are lights that flicker when there is low frequency running through them. Increasing the frequency to 50Hz reduces the flickering to a point where your eyes cannot notice this. This factor has made the 50Hz frequency very popular.

So you might be wondering how household electrical frequency affects a video?

We will get down to this and help you understand this better. You may not notice the flickering of LED lights at 50hz with your own eyes, but in actual sense, it is still there. If for instance, you were to shoot a video using pal 1080i50, with a shutter speed of 1/50, in a place such as Canada using 60Hz LED lighting, you will likely experience flickering on your camera which your human eye will not see.

You may wonder what causes the flicker. In a case where the lighting for your video runs at 60Hz, this translates to on-and-off switching 60 times in any given second. The on and off situation is what causes dimming, though the human eye may not capture this. The camera, however, can capture this which interferes with the quality of your video.

How do I avoid flickering lights in the film industry?

• Synchronization.

It is important that you synchronize the electrical frequency of your LED lights along with the camera. This means you have basically instructed the camera you are using to take a picture every time the ON cycle happens. The two ways to achieve synchronization are explained below.

1. Set your cameras to match that of your environment (PAL or NTSC)

The good news is that most cameras allow you to change from 50Hz (PAL) and 60Hz (NTSC). You only need to ensure the frequency of the camera matches that of your given location( environment). From here, it is up to you to make use of shutter speeds or frame rates that your camera provides.

2. Adjust the shutter speed or angle

In an instance where adjusting the frequency on your camera is impossible, you can work with shutter speed. You need to synchronize your shutter speed with the frequency in your current environment to achieve the desired effect. The tables below give more insight on the right frame rates commonly used as well as the needed shutter speed/angles to work along with.

SHOOTING A VIDEO USING LESS THAN 60HZ LIGHTING ( IN NORTH AMERICA)

The Frame rate	Recommended Shutter speed	Recommended Shutter Angle.
60p/60i	any	any
30p	any	any
24p	any	any
50p/501	1/60,1/120	300,150
25p	1/40,1/60,1/120	225,150,75

SHOOTING A VIDEO USING LESS THAN 50HZ LIGHTING (IN MOST PARTS OF EUROPE AS WELL AS ASIA)

The Frame Rate	Recommended Shutter Speed	Recommended Shutter Angle
60p/60i	1/100	216
30p	1/33.3, 1/50, 1/100	324, 216, 108
24p	1/33.3, 1/50, 1/100	259.2, 172.8, 86.4
50p/50i	Any	Any
25p	Any	any

When shooting videos, clarity is important and the flickering of lights can pose a big challenge while working on a project. Understanding PAL and NTSC is therefore very important. This helps you understand what works best, under what environment, and how best you can achieve your desired results.

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