At times, slow-motion video footage may add drama and elegance, but you need the correct kind of lighting to make it work. This is a crucial component in producing correctly exposed, flicker-free slow-motion videos.
Lighting is essential for converting images into something the human eye understands to be real. Even though we don’t see real things in slow motion, we still have a visual sense of how slowed down action might enhance the reality of what we’re seeing.
If you want to provide the best quality slow-motion video, you’ll need the appropriate lighting equipment. We’ll look at what sort of lighting technology is ideal for slow motion in this section, including:
- HMI
- LED and
- Plasma lighting
VARIABLES IN SLOW MOTION FILMING
There are a few key elements to consider if you’re filming a slow-motion video:
- Frame rates
- Shutter speed
- Lighting
If you don’t control all of the variables, your slow-motion video will be ineffective and choppy. This fluidity is crucial because it ensures that your slow-motion film appears smooth and professional.
If you don’t improve the frame rate, there will be no smooth segway between frames.
As a result, you should shoot at a higher frame rate (e.g., 150fps) and play it back at a lower one (25fps), resulting in a 6 times slower real-time speed (in this scenario). When determining the best frame rate, consider how quickly you need to capture the action you’re filming and the length of the video
When it comes to your film’s look, this all boils down to personal preference. For example, 60fps may be ideal for capturing the slow-motion effect in your film, but you might need a higher frame rate in some cases.
Slowing down the video for playback results in a smooth motion.
Another key factor is the shutter speed. The amount of blur you achieve can be controlled by controlling the shutter speed. The longer the shutter is open, the blurrier the movement becomes.
Set your shutter speed to double your frame rate for a natural-looking amount of motion blur.
However, if you use a too-rapid shutter speed, your slow-motion video will appear jagged, so be cautious. You should also think about how much movement there will be in the subject you are shooting when determining this setting.
Using faster shutter speeds and frame rates also implies that your camera will have less time to capture light for each photograph you take. If you’re going to expose your photos correctly, you’ll need more powerful sources of illumination.
You will end up with slow-motion footage that is underexposed if the correct amount of light isn’t present. You may get a flicker-free video if you use the wrong sort of light.
This is why the lighting of your videos is so important when shooting in slow motion.
WHY FLICKER IS A LIGHTING ISSUE
Because of the frequency of the mains supply current used in tungsten lighting fixtures, there is a flicker. The frequency of the mains supply in the UK is 50Hz, whereas it is 60Hz in the USA. The number of complete AC sine waves per second is known as hertz.
The frequency of an HMI light source is usually drawn from the supply ballast, which is typically set between 50Hz, 60Hz, and “flicker-free” (typically 100Hz) or in specialized ballasts like the ones we offer as standard with our ARRI M Series lighting. For ultra-slow-motion pictures captured with our Vision Research Phantom
Most illumination sources employed in filming do not produce a steady luminous flux, but instead, have an intensity that varies with the supply’s voltage. The mains frequency changes its polarity per second, so light intensity pulses at the same rate as this mains frequency.
This is a frequent problem caused by mismatched frame rates. When filming lighting, you’re employing set framerates that, when mismatched with the lighting frequency, can cause the image to flicker or roll. In this way, the camera’s sensor frame rate works in much the same manner as the AC mains supply’s frequency. 25p
In general, there will be no flicker if the frame rate is a whole multiple of the lighting frequency. When the frame rate differs from the frequency, for example when recording 25p in America where the mains supply is 60Hz, flicker occurs. A 50Hz lighting source is far too slow to provide adequate illumination at 1000fps.
To fix the problem, adjust the frame rate, shutter speed, or lighting frequency to match. The choice of the light source is critical in lowering the flicker rate. For slow-motion filming, the higher the frequency, the better.
FLICKER-FREE LIGHTING
Flicker will not be an issue if you are shooting outside using the sun and reflectors as your light sources. Most electrically generated light sources, however, will flicker to some extent as previously said. most electronically produced illumination sources will flicker in some way; it’s all about how much they flicker for the viewer.
Some artificial light sources are better than others at providing flicker-free light.
Flicker is determined by a variety of factors, depending on the form of illumination:
HMI LAMPS
HMI lamps can be used with flicker-free electronic ballasts. HMI is a type of hydrargyrum medium-arc iodide. Instead of an incandescent bulb, these lights employ an arc lamp.
The electronic ballast is a gadget that generates an ignition pulse and controls the arc. The sine wave is changed into a square wave, keeping the light constant for longer after zero-crossing (the point where there is no voltage present).
The frequency of a flicker-free HMI lamp is typically 75 to 100Hz. The gap between the electrodes widens over time, with the arc extinguishing for longer periods at zero-crossings. This can raise the flicker factor to above 3%, which indicates that it’s time to replace the bulb.
LED LIGHTS
LEDs are susceptible to flicker, especially if you dim them. Professional-grade LED lighting fixtures to regulate the frequency of each individual LED on the panel to minimize flickering (and price!).
Because of this method, most LED fixtures are now regulated to far higher frequencies than we can capture with specialist cameras. The huge new dot LED technology is rated at more than 10,000Hz! This makes them a great fit for high-frame-rate filming.
TUNGSTEN LAMPS
Tungsten lamps acquire their frequency from the mains supply, as previously said. If you dim tungsten lamps, you are changing the amount of current that it receives and hence the frequency and flicker.
FLUORESCENT LAMPS
Florescent lights can be operated on either electronic or magnetic ballasts, and this minimizes flicker.
When a magnetic ballast is used with a fluorescent lamp, the flicker rate ranges from 30% to 60% (as found in building strip lights). Electronic ballasts can be made to have a flicker factor of 0% to 12%.
Magnetic ballasts create a lot of wild flickers when you shoot with non-flicker free light sources, so the frame rate and/or shutter angle will need to be adjusted.
Although there are a few more options for flicker-free lighting available, there are an increasing number of sophisticated choices that provide filmmakers greater freedom when it comes to recording in fluid slow motion.
HIGH-SPEED BALLASTS FOR HMI LIGHTING
Arc wander is a form of flicker that can appear in HMI lighting due to electronic ballast. Arc wander occurs when a plasmatic hot spot moves within the bulb, causing the light output to vary.
HMI bulbs with a standard electronic ballast can result in an apparent shimmering effect and a rapid colour shift, as shown above. This implies that you cannot ensure flicker-free lighting with HMI lamps using a conventional electronic ballast.
High-frequency ballasts for HMI lamps are another option. These can significantly reduce or even eliminate flicker. Flicker-free pictures of excellent quality with frame rates as high as 1000fps are possible with these high-speed ballasts.
M SERIES AND MAX TECHNOLOGY
The ARRI M Series of daylight HMI bulbs utilize MAX technology to give cutting-edge illumination. For this lighting, MAX Technology developed a unique reflector design that generates extremely brilliant, open-face lights.
The M Series includes five HMI lamp heads, ranging in wattage from 800 to 18,000 watts. Because they have eliminated the need for big lenses, these lights provide for excellent handling and a high level of lighting consistency. This makes them perfect for capturing excellent slow-motion footage at high frame rates.
ADVANCES IN LED LIGHTING
LED lights that are breaking new ground in terms of power and mobility have now been developed.
- The Litepanels Gemini 2×1 and 1×1 fixtures provide an even, soft light that’s ideal for slow-motion fill applications. These battery-operated LED lights are modular and may be linked together to make a 4×1 or 4×2 array.
- Stella Pro Lighting also produces cutting-edge LED lighting, such as the Stella Pro 10000c ultra-powerful LED lamp. This corded light emits cinematic-quality illumination on a par with HMI lights and has a consistent, regulated, and dependable output that makes it ideal for slow-motion filming. It generates 10,000 lumens using sophisticated flicker-free firmware. The Stella Pro10000c’s integrated variable speed fan maintains constant output at its high-power levels by automatically operating when the light produced reaches 5,000 lumens.
- The ARRI L Series incorporates a smooth light field and continuous focus ability into its LED technology. This gives users complete control over the colour and intensity of LED lighting, making it ideal for professional-level slow-motion shooting with high quantities of frames per second.
THE WIRELESS OPTION FOR LED LIGHTING
Going wireless is another sophisticated alternative for LED illumination in slow-motion movies. Astera produces high-end, battery-operated lights. These remote-controlled lights are extremely portable and made specifically for filming a wide range of materials.
The Astera Wireless LED Lights are flicker-free. To do so, it employs scrambled pulse width modulation (S-PWM). The duty cycle of an LED is the percentage of time the light is on. normal pulse width modulation is a technique for dimming LEDs by turning them on and off rapidly. This is known as pulsing. Visually, this results in a dim, steady glow.
Scrambled pulse width modulation is another refinement of this technique. It scrambles the LED channels’ pulses into sub-pulses. This allows the channels to communicate and minimize the instances when they will all be off. Flicking in high-level recordings may be reduced because of this.
PLASMA LIGHTING
Slow-motion filming is now possible thanks to advancements in HMI and LED lighting technology, which has made them flexible and versatile.
However, there is another option, and that is plasma lighting. There are no electrodes in a plasma light; instead, radio waves (RF) pass energy into a quartz bulb containing a combination of noble gases and metal halides. The gases become ionized because of an electrical field in the centre of the bulb. They heat up, evaporating metallic halides from the mixture to produce a bright light that is flicker-free since it is disconnected from mains/ballast frequency.
High-speed lighting from a high-power source combines the advantages of several light forms. They combine the day brightness and output of HMIs with the dependability, longevity, and energy savings of LEDs. The Hive Plasma 1000 flicker-free illumination is provided by a fast light source.
It runs much faster than any existing frame rates, with cycles of 450 billion times per second. This is well in excess of the most rapid LED light displays. Flicker from a plasma light can only be detected at the rate of 225 million frames per second, which is far lower than the maximum operating speed of this machine.
Plasma lighting at this level is flicker-free and provides a cutting-edge solution for high-quality slow-motion video, in practice. Lower heat generation and full-spectrum daylight are other advantages of plasma lights.
Plasma bulbs are extremely durable, with a lifespan of 30,000 hours and 50,000 hours of light output thanks to their absence of an electric filament.
THE FUTURE OF LIGHTING
In the constantly developing video market, various forms of lighting are vying for attention. Each has its own set of benefits, such as LED lights’ energy efficiency and environmental credentials, as well as plasma lights’ flicker-free qualities.
In terms of raw performance, for example, plasma may provide ideal conditions for even the most demanding of slow-motion sequences. However, the lens-free M Series offers its own variations in flexibility, cost, and durability. The future of lighting will be founded on more variety and continual innovation in lighting performance.
Slow-motion video will continue to be a powerful, visual tool, whichever lighting technique you use. It may add emphasis or raise the anticipation of an audience. Slo-mo is very good at focusing the attention of the viewer on the narrative.
Why not contact Pro-Motion hire to find out what kind of lighting you need for your slow-motion filming.
