Light for video

Many photographers build their lighting around flash. Flash is powerful, portable and freezes motion, but it is useless for video, which needs light that stays on continuously and stays consistent for the length of a shot and a scene. Moving to continuous light changes how you think about power, color quality, batteries, heat and flicker, and it changes how you work with daylight that shifts during a long interview. This lesson covers continuous light for hybrid shooters: choosing LED fixtures, measuring how much light you need, mixing color temperatures, avoiding flicker, lighting interviews and keeping light consistent. CINE-220 covers fixtures, photometrics and the electric department in depth, and CINE-221 covers motivated and naturalistic lighting for drama; this lesson stays with the small kits that one or two people can carry and set up quickly.

From flash to continuous light

What you know about light quality transfers fully: a large source close to the subject is soft, a small or distant source is hard, light falls off with distance, and direction shapes the face. What changes is power and convenience. A 600-watt-second strobe produces a burst of light far brighter than a portable LED can sustain; a typical 60-watt LED panel gives roughly the light of a modeling lamp. In return, continuous light is what-you-see-is-what-you-get, which makes it easy to judge shadows and ratios on the monitor, and it works for both stills and video. Many hybrid shooters now light stills with LEDs too when the subject is static, accepting higher ISO in exchange for a single setup.

Because continuous sources are weaker, you will usually work closer, use the sun or windows as your main source more often, and rely on reflectors and negative fill (black surfaces that absorb light) to shape it. Modern cameras' clean high-ISO performance makes this practical.

How much light do you need?

Incident light is measured in lux. You can estimate the illuminance needed for a given exposure using the incident-meter equation, with a calibration constant of about 250 for flat-receptor incident meters.

Here \( E \) is illuminance in lux, \( N \) the f-number, \( t \) the shutter time in seconds, \( S \) the ISO and \( C \) the calibration constant. The equation shows why video lighting is gentler than many photographers expect: at ISO 800 and 1/50 second, you need only a little over 100 lux on a face for f/2.8.

def lux_needed(f, shutter, iso, c=250):
    return f ** 2 * c / (shutter * iso)
for f, shutter, iso in [(2.8, 1/50, 800), (4, 1/50, 800), (2.8, 1/50, 3200), (5.6, 1/60, 400)]:
    print(f'f/{f} 1/{round(1 / shutter)} ISO {iso}: about {lux_needed(f, shutter, iso):.0f} lux')

f/2.8 1/50 ISO 800: about 122 lux
f/4 1/50 ISO 800: about 250 lux
f/2.8 1/50 ISO 3200: about 31 lux
f/5.6 1/60 ISO 400: about 1176 lux

Choosing LED fixtures

LED fixtures come as panels, which are flat and fairly soft on their own; point-source lights (often called COB fixtures) that take Bowens-mount softboxes and reflectors, much like strobes; tubes, which are good for practicals, accents and tight spaces; and small on-camera lights, which are useful for run-and-gun but flatten faces. Bi-color fixtures blend warm and cool LEDs to give a range such as 2700 K to 6500 K. RGB or full-color fixtures can produce any hue and often have better color accuracy across the range, plus effects and gel emulation.

Color quality matters more for video than many photographers expect, because grading cannot easily fix spiky light spectra across a whole scene. The Color Rendering Index (CRI) is the familiar measure, but it was designed for architectural lighting. The Television Lighting Consistency Index (TLCI) was designed for cameras; values above about 90 need little correction. TM-30 and the Spectral Similarity Index (SSI) give more detail. Look for independent measurements, not just marketing claims.

Color temperature and mixing sources

Every location has its own mix of light: daylight through windows at roughly 5000 to 6500 K, warm tungsten or LED practicals at 2700 to 3200 K, fluorescent or cheap LED ceiling lights with a green tint. In stills you can often correct a single frame globally; in video, mixed light across a face or between shots becomes very obvious and hard to fix. Decide what the main source in the scene is and match your lights to it, or change the room.

Color correction gels are measured in mireds, a unit that makes color temperature shifts additive. The mired value of a source is one million divided by its Kelvin temperature. A gel shifts the mired value by a fixed amount regardless of starting point.

Flicker and shutter speed

Lights powered by alternating current flicker at twice the mains frequency. Canada and the United States use 60 Hz mains, so fluorescent tubes, discharge lamps and many cheap LEDs pulse 120 times per second. If the camera's shutter is not a multiple of the flicker period, successive frames catch different points in the cycle and the image pulses or shows rolling dark bands. At 60 Hz, shutter speeds of 1/60 and 1/120 second (and 1/30, 1/40 and other multiples of 1/120) avoid flicker from mains lights; the 1/50 second that suits 24 fps can show banding.

LEDs and screens add other flicker sources. Many LED fixtures and bulbs dim using pulse width modulation (PWM), switching on and off rapidly; at low dimming levels this can flicker at frequencies unrelated to the mains. Computer monitors and LED video walls have their own refresh rates. Use the camera's flicker reduction or synchro scan feature, which allows fine shutter adjustments such as 1/50.3, to remove banding, and choose fixtures marketed as flicker-free at all dimming levels for your own kit.

Lighting an interview with a small kit

The classic interview setup uses three roles. The key light is the main source, usually placed 30 to 45 degrees to one side of the camera and slightly above eye level, often on the side the subject faces (short-side or far-side lighting, which places the key on the side of the face away from the camera and gives more shape). Fill light softens shadows on the other side; in a small kit, fill often comes from a reflector, a dimmed panel or the room itself, and many interviews use negative fill instead to deepen shadows. A back light or hair light separates the subject from the background. A background light or practical lamp adds depth.

A window can be the key: place the subject so the window is to one side and slightly in front, the camera on the shadow side looking across, and add a little fill or negative fill. Watch out for changing daylight. Clouds can change window light by two or three stops within a minute, and an interview may last half an hour; editors cannot cut between answers lit at different brightness without it showing. If daylight is unstable, use your LED key strongly enough to dominate, or diffuse the window and accept a smaller contribution from it.

Ratios and mood

The lighting ratio compares the light on the key side of the face with the fill side. A 2:1 ratio (one stop) looks bright and open, suiting corporate and educational pieces; 4:1 (two stops) looks more dramatic and suits documentary and brand storytelling; 8:1 or more looks moody and theatrical. Measure ratios with a light meter, the camera's waveform or false color, or simply by switching each light off and on and noting the change in exposure. Agree the look with the client in advance; a bank's annual report video and a craft distillery's story film call for different moods.

Power, batteries and heat

Continuous light needs continuous power. Most small LEDs run from mains, from batteries in the fixture or from external batteries such as V-mount packs. Runtime is approximately the battery's watt-hours divided by the fixture's power draw, reduced for conversion losses and cold temperatures.

Battery travel rules matter for photographers who fly. Under the aviation rules applied by Transport Canada and by the US Federal Aviation Administration, both based on international standards, spare lithium-ion batteries must travel in carry-on baggage; batteries up to 100 Wh are generally allowed without airline approval, and those between 100 and 160 Wh need airline approval and are usually limited to two spares per passenger. This is why 98 Wh V-mount batteries are popular. Check the current rules with your airline before each trip. LED fixtures run much cooler than tungsten, but point sources and their power supplies still get hot; keep modifiers clear of hot surfaces and secure stands with sandbags, especially in public spaces (CINE-340 covers set safety).