Film & Video Lighting Dictionary

AC power uses a supply whose voltage changes polarity periodically. Lighting equipment specifies its accepted AC voltage range and frequency.

Amperage is electric current measured in amperes. Fixture current depends on the supply, input power and operating conditions; wattage alone is insufficient for AC loads.

Apparent power is RMS voltage multiplied by RMS current for a single-phase AC load, expressed in volt-amperes. It differs from real power in watts.

Art-Net transports lighting-control data over an IP network. Controllers and nodes can use it to distribute multiple DMX universes to compatible equipment.

Back light comes from behind a subject relative to the camera. It can create separation or an edge highlight; hair and rim lights are related applications.

Beam angle describes angular beam width, conventionally between the directions where intensity falls to 50% of the maximum. Check the manufacturer’s definition.

A bi-colour fixture produces adjustable white light over a stated CCT range. The term describes its function; it does not guarantee full-colour output or tint control.

A book light bounces a source and then passes that reflected light through diffusion. The setup creates a broad source while giving control over its coverage.

Bounce light reaches a subject after reflecting from another surface. The surface’s size, texture and colour affect the resulting illumination.

The candela (cd) measures luminous intensity in a particular direction. It describes concentration of light, rather than total output or illuminance at a surface.

Correlated colour temperature (CCT) describes the warm-to-cool appearance of white light in kelvin (K). It does not describe colour rendering or green–magenta tint.

Colour mixing combines light components to produce a target colour. LED fixtures commonly offer CCT, HSI, RGB or xy controls for different ways of specifying that target.

CRI, or colour rendering index, compares colour appearance under a light with a reference. The commonly quoted Ra score averages eight test colours.

CRMX is LumenRadio’s wireless-DMX technology. A working link needs compatible transmitting and receiving equipment as well as a correctly configured lighting patch.

CTB is a blue correction filter that raises a light’s correlated colour temperature. It is often used to bring tungsten light toward daylight balance.

CTO is an orange correction filter that lowers a light’s correlated colour temperature. Full and fractional strengths provide different amounts of warming.

DC power uses a supply with fixed polarity. A compatible lighting connection must match the required voltage, polarity, connector wiring and available current.

Diffusion scatters light passing through a material. The size and placement of the illuminated diffusion surface help determine how soft the light appears.

A dimming curve maps a control value to light output. It changes how a fade responds across the control range and is separate from PWM frequency.

A DMX start address identifies the first control slot a fixture reads within its universe. Its selected personality determines how many following slots it uses.

A DMX personality defines which parameters a fixture exposes and how its control slots are arranged. The controller profile must match the mode selected on the fixture.

A DMX universe contains up to 512 control slots. It is a block of control data, so the number of fixtures it can carry depends on their selected modes.

DMX512 is a lighting-control protocol. One universe carries up to 512 control slots, and a fixture can use several slots according to its selected personality.

Duv describes a white light’s distance above or below the Planckian locus. It helps identify tint differences that a CCT reading alone cannot show.

Falloff is a reduction in light level across a scene or with distance. Distance, beam shape, source size and surrounding bounce affect the pattern.

Feathering means aiming a light so the subject uses a selected part of its beam, often away from the centre. It changes coverage, exposure and spill.

Field angle is conventionally measured between the directions where intensity falls to 10% of the maximum. It includes more of a beam’s outer spill than beam angle.

Fill light raises the illumination in shadows created by the key. It controls shadow detail and contrast without needing to become a second dominant direction.

A flag is an opaque light-control surface used to block a selected light path. It can cut spill, protect the lens from flare or provide negative fill.

Flicker is variation in light output over time. A camera may record brightness changes or rolling bands even when the source looks steady to the eye.

A foot-candle (fc) is a unit of illuminance equal to one lumen per square foot. One foot-candle equals approximately 10.764 lux.

A light-control grid limits the directions in which light can leave a fixture or modifier. It helps reduce spill while retaining the source’s useful area.

Hard light creates a clearly defined shadow edge. It comes from a source that appears small from the subject’s position.

An incident light meter measures light arriving at the subject. It helps set exposure and compare lighting levels without depending on the subject’s reflectance.

Inrush current is a brief current surge when equipment is energized. It can be much higher than normal operating current and must be read with its duration and test conditions.

For a point-source approximation, illuminance varies with the inverse square of distance. Doubling distance gives one-quarter the illuminance, a two-stop reduction.

The key light establishes the main lighting direction and modelling of a subject. It is a role in the scene, not a particular type of fixture.

A lighting ratio compares two measured light levels. State whether it means separate key and fill contributions or the resulting bright and shadow sides.

The lumen (lm) is the unit of luminous flux. It describes visible-light output, while lux describes how much light reaches a surface.

Luminance describes light leaving a surface in a particular direction, measured in candelas per square metre. It differs from lux, which measures arriving light.

Lux (lx) is a unit of illuminance: the amount of light arriving at a surface. Fixture output figures in lux need a distance and measurement conditions to be useful.

Minusgreen is a magenta correction filter used to reduce a source’s green cast. Choose its strength by testing the actual light, camera and required match.

Negative fill uses a dark, low-reflectance surface to reduce ambient or bounced light reaching a subject, usually to deepen shadows and increase contrast.

Photometrics are measurements describing a light’s output and distribution. Useful comparisons identify distance, CCT, optics, dimming level and measurement position.

Plusgreen is a green correction filter used to shift a source toward green. It can help match other lighting before a shared camera or post-production correction.

Power factor is real AC power in watts divided by apparent power in volt-amperes. It affects the current required for a given electrical input power.

PWM controls LED output by changing the proportion of each switching cycle spent on. Camera timing can reveal this modulation as flicker or banding.

RDM adds two-way management to compatible DMX512 systems, including fixture discovery, remote configuration and supported status reporting.

A reflected light meter reads light coming from the scene toward the camera. Its reading depends on the surfaces and viewing area included in the measurement.

RGBACL identifies red, green, blue, amber, cyan and lime components. It may describe an emitter system or a control mode, depending on the manufacturer.

RGBWW commonly combines red, green and blue LEDs with warm-white and cool-white emitters. The manufacturer’s colour engine and calibration determine the result.

sACN, or streaming ACN, transports DMX-style lighting data over an IP network. It is specified by ANSI E1.31 and supports multiple identified universes.

Soft light creates a gradual transition between light and shadow. Its source appears large from the subject’s position.

Spill is light reaching an area outside the intended lighting effect. It can brighten a background, wash out shadows or strike the camera lens.

SSI compares the spectrum of a light with a stated reference spectrum. Read the reference alongside the score when comparing lighting specifications.

A stop is a doubling or halving of exposure or measured light. It lets crews compare lighting changes, meter readings and aperture settings on the same scale.

TLCI evaluates a light’s colour performance using a model of a television camera and display system. It helps flag potential colour-correction problems.

TM-30 evaluates colour rendition using 99 colour samples. Its fidelity index, gamut index and graphics describe different aspects of a light’s colour behaviour.

Voltage is electrical potential difference, measured in volts. A fixture must receive the voltage range and AC or DC supply type specified for its input.

A watt (W) is a unit of power equal to one joule per second. Electrical wattage describes energy use, not how much useful light reaches a subject.