Light Output & Measurement
Lighting output is described using several different measurements. Some describe how much light a source produces, while others describe how much light actually reaches a surface.
Lux
Lux measures the amount of light reaching a surface. One lux equals one lumen distributed over one square metre.
Why it matters: Lux is useful when planning how bright a worktop, office desk, retail display or room should be. It describes the light arriving at the task area rather than simply the output of the lamp.
Practical note: The same luminaire can produce different lux levels depending on mounting height, beam angle, distance and placement.
Related: Lux & Lumens Lighting Guide · Lux & Lumens Calculator
Lumen
A lumen, written lm, measures the total amount of visible light produced by a light source.
Why it matters: Lumens provide a better indication of light output than wattage. Two LED lamps can consume the same number of watts while producing different amounts of light.
Practical note: More lumens do not automatically mean better lighting. Distribution, beam angle and fixture placement determine where those lumens actually go.
Related: Lux & Lumens Lighting Guide · Lux & Lumens Calculator
Watt
A watt, written W, measures electrical power consumption. It does not directly measure brightness.
Why it matters: With LED lighting, wattage is mainly useful for understanding energy use and electrical load. Light output should normally be compared using lumens rather than watts alone.
Practical note: A more efficient LED product can produce more light while consuming fewer watts.
Luminous Efficacy
Luminous efficacy describes how efficiently a light source converts electrical power into visible light. It is commonly expressed in lumens per watt (lm/W).
Why it matters: A higher lm/W value generally means more light is produced for the same electrical power.
Practical note: Efficacy is useful when comparing energy performance, but it should not replace considerations such as CRI, glare, beam quality or colour temperature.
Illuminance
Illuminance is the technical term for the amount of light falling onto a surface and is measured in lux.
Why it matters: Lighting designers use illuminance when determining whether a working surface, circulation area or room receives an appropriate quantity of light.
Practical note: When we refer to a target of 300 lux or 500 lux, we are describing illuminance.
Luminous Flux
Luminous flux is the technical term for the total quantity of visible light emitted by a source. It is measured in lumens.
Why it matters: It provides a standardized way to compare the overall visible output of different light sources.
Practical note: Luminous flux describes total output, not how concentrated or widely distributed that light will be.
Candela
Candela, written cd, measures luminous intensity in a particular direction.
Why it matters: It helps describe how strongly a light source sends light in a specific direction, which can be important for spotlights, projectors and narrow-beam luminaires.
Practical note: Two luminaires can have similar lumen output but very different candela values if one concentrates its light into a narrower beam.
Light Quality
Brightness is only one part of lighting quality. Colour appearance, colour rendering, glare, consistency and flicker can significantly affect how a space looks and feels.
CCT — Correlated Colour Temperature
CCT describes the colour appearance of white light and is measured in Kelvin (K).
Lower values such as 2700K appear warmer and more yellow, while higher values such as 4000K appear more neutral or cooler.
Why it matters: CCT influences the atmosphere of a room and how materials, furniture and finishes are perceived.
Practical note: 3000K is commonly used in warm residential environments, while 4000K can create a cleaner, more neutral appearance.
Related: 3000K vs 4000K Lighting Guide
CRI — Colour Rendering Index
CRI describes how accurately a light source renders colours compared with a reference source.
The general CRI value is expressed on a scale up to 100.
Why it matters: Good colour rendering is particularly useful for skin tones, food, clothing, artwork, interior finishes and retail displays.
Practical note: CRI 90+ is often a strong choice for applications where accurate colour appearance is important.
R9
R9 is an additional colour-rendering value that describes how well a light source reproduces strong red tones.
Why it matters: Red reproduction affects the appearance of skin tones, food, fabrics, wood and many interior finishes.
Practical note: Two products can have similar general CRI values but perform differently in R9, so it can be useful for colour-sensitive applications.
SDCM
SDCM stands for Standard Deviation Colour Matching and describes how closely the colour appearance of different light sources matches.
Lower SDCM values indicate tighter colour consistency.
Why it matters: Colour differences can become noticeable when several luminaires or LED strips are installed next to each other.
Practical note: Good colour consistency is particularly important in linear lighting, retail displays, wall washing and larger installations.
MacAdam Ellipse
A MacAdam ellipse is a way of describing differences in perceived light colour.
The concept is closely related to SDCM: smaller colour-step ranges represent tighter consistency between light sources.
Why it matters: It helps explain why two LEDs labelled with the same CCT can still appear slightly different when viewed together.
UGR — Unified Glare Rating
UGR is a method used to evaluate discomfort glare in indoor lighting installations.
Lower UGR values generally indicate better glare control for the assessed installation.
Why it matters: Excessive glare can make offices, workspaces and commercial environments uncomfortable even when the light level itself is adequate.
Practical note: UGR depends on the complete lighting arrangement, room geometry, viewing position and luminaires. It should not be treated simply as a universal quality number for one fixture.
Flicker
Flicker refers to rapid changes in light output caused by variations in the electrical supply, driver or control system.
Some flicker is visible, while higher-frequency modulation may not be immediately noticeable.
Why it matters: Poorly controlled flicker can cause visual discomfort and may become particularly noticeable when dimming or recording video.
Practical note: Driver quality and dimmer compatibility are important when evaluating flicker performance.
Beam & Distribution
How light is distributed can be just as important as how much light a fixture produces. Beam characteristics determine whether light is concentrated, spread widely or used to highlight a surface.
Beam Angle
Beam angle describes how widely a luminaire spreads its main beam of light.
A narrower beam concentrates light into a smaller area, while a wider beam covers a larger area.
Why it matters: Beam angle affects spotlight spacing, accent lighting, ceiling layouts and the size of the illuminated area.
Practical note: Mounting height also affects coverage—the same beam becomes wider as the distance from the illuminated surface increases.
Related: Beam Angle Guide · Beam Angle Calculator
Field Angle
Field angle describes the wider area around the main beam where useful light is still present, but at a lower intensity.
Why it matters: It helps describe the softer outer portion of a light distribution beyond the primary beam.
Practical note: Field angle is common in detailed photometric specifications but is not published for every retail lighting product.
Wall Washing
Wall washing uses broad, relatively even light to illuminate a wall or vertical surface.
Why it matters: It can make a space feel brighter, emphasize architecture and create a more uniform appearance across walls.
Practical note: Fixture distance, spacing and beam distribution all influence how evenly the wall is illuminated.
Wall Grazing
Wall grazing places light close to a textured wall so that light and shadow emphasize the surface relief.
Why it matters: It is useful for stone, brick, textured plaster and other architectural surfaces where texture should remain visible.
Practical note: Grazing and wall washing create very different effects. Grazing emphasizes texture, while wall washing aims for greater uniformity.
Light Spill
Light spill is light that reaches areas outside the intended target.
Why it matters: Excessive spill can create glare, reduce contrast, disturb neighbouring areas or waste light.
Practical note: Better beam control, aiming and fixture placement can reduce unwanted spill.
Electrical & Control
LED lighting relies on compatible electrical components and control methods. Understanding drivers, voltage and dimming helps avoid performance and compatibility problems.
LED Driver
An LED driver supplies and regulates the electrical power required by an LED light source.
Why it matters: LEDs require suitable voltage and current conditions to operate correctly. An incompatible or incorrectly sized driver can cause poor performance, flicker or failure.
Practical note: Always match the driver type and electrical specifications to the LED product rather than selecting a driver only by wattage.
Related: LED Strip Driver Calculator
Constant Voltage
A constant-voltage driver supplies a fixed output voltage, commonly 12V or 24V, while the connected load determines the current drawn.
Why it matters: Constant-voltage systems are commonly used with LED strip lighting and certain modular LED products.
Practical note: The strip voltage and driver output voltage must match.
Constant Current
A constant-current driver regulates the electrical current supplied to the LED while allowing the voltage to vary within a specified range.
Why it matters: Many integrated LED spotlights, downlights and modules use constant-current drivers.
Practical note: Replacement drivers must be matched carefully to the required output current and voltage range.
TRIAC Dimming
TRIAC dimming is a mains-voltage dimming method commonly used in residential lighting.
It controls power by modifying part of the AC waveform supplied to a compatible driver or lamp.
Why it matters: It can allow familiar wall dimmers to control LED lighting without a separate control network.
Practical note: The dimmer, driver and LED load must be compatible to achieve smooth dimming.
0–10V Dimming
0–10V is an analogue lighting-control method where a low-voltage control signal adjusts the light output of a compatible driver.
Why it matters: It is widely used in commercial lighting and building-control applications.
Practical note: It generally requires dedicated control wiring in addition to the mains power connection.
DALI
DALI stands for Digital Addressable Lighting Interface.
It is a digital lighting-control protocol that allows compatible luminaires and control devices to communicate through a dedicated control system.
Why it matters: DALI can support individual addressing, scenes, groups and more advanced control strategies.
Practical note: It is commonly used where lighting needs more structured or centralized control than a conventional wall dimmer.
PWM — Pulse Width Modulation
PWM controls light output by rapidly switching the electrical signal on and off and changing the proportion of time it remains on.
Why it matters: It is commonly used in LED strip dimming and other low-voltage LED systems.
Practical note: The switching frequency and control quality can affect flicker and camera performance.
Power Factor
Power factor describes how effectively an electrical load uses the power supplied to it.
A value closer to 1 generally indicates better utilization of the electrical supply.
Why it matters: Power factor becomes particularly relevant in larger commercial installations containing many LED drivers.
Surge Protection
Surge protection helps protect electrical equipment from short-duration voltage spikes.
Why it matters: LED drivers and electronic lighting systems can be sensitive to electrical disturbances.
Practical note: Protection requirements depend on the installation, electrical system and local conditions. Surge protection should form part of the wider electrical design rather than being treated as a property of the LED alone.
LED Systems
LED strip and linear lighting systems combine the light source, profile, diffuser, driver and electrical layout. Each component affects the final appearance and performance.
LED Strip
LED strip is a flexible or rigid circuit containing multiple LEDs arranged along a continuous length.
Why it matters: It can provide task lighting, indirect light, shelf lighting, cove lighting and architectural linear effects.
Practical note: Strip voltage, wattage per metre, CCT, CRI, driver capacity and installation length should be considered together.
Related: LED Strip Lighting Design Guide · LED Strip Driver Calculator
LED Profile
An LED profile is usually an aluminum channel designed to house LED strip.
Why it matters: Profiles create a cleaner installation, help manage heat and provide a mounting surface for a diffuser.
Practical note: Profile depth and diffuser type influence how visible individual LED points remain.
Diffuser
A diffuser is a translucent cover used to soften and distribute light.
Why it matters: In LED profiles, a diffuser can reduce visible LED dots, protect the strip and create a more continuous appearance.
Practical note: Greater diffusion can improve visual uniformity but may also reduce the amount of light transmitted.
COB LED Strip
COB stands for Chip on Board.
COB LED strip uses many closely spaced LED chips to create a more continuous line of light than many traditional strip designs.
Why it matters: It can reduce the appearance of individual LED dots, particularly in shallow profiles or visible installations.
SMD LED
SMD stands for Surface-Mounted Device.
SMD LEDs are individual LED packages mounted onto a circuit board and are widely used in lamps, luminaires and LED strips.
Why it matters: Different SMD designs can vary in output, efficiency, colour quality and spacing.
Voltage Drop
Voltage drop is the reduction in electrical voltage that occurs along cables or LED strip as current travels through the circuit.
Why it matters: On longer LED-strip runs, excessive voltage drop can cause the end of the strip to appear dimmer or change colour slightly.
Practical note: Cable size, run length, strip wattage and power-feed arrangement all affect voltage drop.
Power Injection
Power injection means supplying electrical power to an LED-strip installation at additional points rather than feeding the entire run from only one end.
Why it matters: It can reduce voltage drop and help maintain more consistent brightness across longer installations.
Practical note: Power injection must be designed correctly for the voltage, current and wiring arrangement of the system.
Protection & Durability
Lighting products can face dust, moisture, impact and weather exposure. Protection ratings help indicate whether an enclosure is suitable for particular environmental conditions.
IP Rating
IP stands for Ingress Protection.
An IP rating uses two digits to indicate how an enclosure is protected against solid objects and water.
The first digit relates to solid-particle protection.
The second digit relates to water protection.
Common examples include:
- IP20 — basic indoor protection with no meaningful water protection
- IP44 — protection against solid objects larger than 1 mm and splashing water
- IP65 — dust-tight and protected against water jets
- IP67 — dust-tight and protected against temporary immersion under defined test conditions
Why it matters: The required IP rating depends on where and how the product will be installed.
Practical note: A higher number is not automatically “better” for every application. Choose protection appropriate to the environment and applicable installation requirements.
Related: IP Ratings Explained · Outdoor Lighting Guide
IK Rating
IK rating describes the resistance of an electrical enclosure to mechanical impact.
Why it matters: It can be important for exterior fixtures, public areas, commercial environments and locations where luminaires may be exposed to accidental impact.
Practical note: IK and IP describe different things. IP relates to ingress of solids and water, while IK relates to mechanical impact resistance.
Fixture Types
Fixture names describe how a light is mounted, shaped or used. Understanding the basic types makes it easier to compare products and choose the right family for an application.
Downlight
A downlight is a ceiling-mounted luminaire designed primarily to direct light downward.
It can be recessed into the ceiling or surface-mounted depending on the design.
Typical uses: general lighting, circulation areas, kitchens, offices and commercial spaces.
Spotlight
A spotlight produces relatively controlled, directional light and is commonly used for task or accent lighting.
Why it matters: Spotlights allow more precise control than broad general-lighting fixtures.
Practical note: Beam angle, output and aiming capability determine how concentrated the effect will be.
Related: Spotlight Layout Calculator · Beam Angle Guide
Track Light
A track light is a luminaire mounted onto an electrified track system.
Fixtures can normally be positioned along the track and, depending on the system, aimed toward different areas.
Typical uses: retail, galleries, residential interiors and spaces where flexible directional lighting is useful.
Magnetic Track Light
A magnetic track light is part of a compatible low-voltage track system where lighting modules connect mechanically and electrically to the track, commonly using magnetic attachment.
Why it matters: These systems can support different module types within one coordinated lighting architecture.
Practical note: Components from different magnetic systems are not automatically compatible.
Related: Magnetic Track Lighting vs Recessed Spotlights · Modular Lighting Planner
Pendant Light
A pendant light hangs from the ceiling using a cable, rod or chain.
Typical uses: kitchen islands, dining tables, bedside areas, counters and decorative focal points.
Practical note: Fixture size, hanging height and spacing should relate to the furniture or surface below rather than the room dimensions alone.
Chandelier
A chandelier is a decorative suspended fixture, often using multiple arms, lamps or light sources.
Why it matters: Chandeliers usually serve both as illumination and as a major visual element within the room.
Practical note: Diameter, hanging height and ceiling height should be considered together.
Related: How to Choose the Right Chandelier Size
Wall Light
A wall light is mounted directly onto a vertical surface.
Depending on the design, it may provide ambient, decorative, task, upward or downward light.
Typical uses: bedrooms, corridors, bathrooms, façades, entrances and decorative interiors.
Bollard Light
A bollard light is a low freestanding outdoor fixture commonly used along paths, gardens, entrances and landscape areas.
Why it matters: It can provide low-level guidance and area lighting without requiring overhead fixtures.
Practical note: Spacing, glare control and light distribution are important when planning multiple bollards.
In-Ground Light
An in-ground light is installed into the ground or another horizontal surface.
It is commonly used for architectural, façade and landscape accent lighting.
Practical note: Drainage, installation method, load conditions and suitable IP protection are particularly important for in-ground applications.
Panel Light
A panel light uses a broad luminous surface to provide relatively uniform light.
Typical uses: offices, commercial interiors, corridors and general ceiling lighting.
Practical note: Panel lights may be recessed, surface-mounted or suspended depending on the product and ceiling system.
Surface-Mounted Light
A surface-mounted light attaches directly onto the visible surface of a ceiling or wall rather than being recessed into it.
Why it matters: It can be useful where ceiling void depth is limited or where recessed installation is not possible.
Lighting Design Terms
Lighting design combines different types of light to support visibility, comfort, atmosphere and architecture. These terms describe the role that light plays within a space.
General Lighting
General lighting provides the basic overall illumination needed to move through and use a space comfortably.
It is sometimes also called ambient lighting, although the two terms can be used slightly differently depending on design context.
Ambient Lighting
Ambient lighting creates the overall background level and atmosphere of a space.
It may come from ceiling fixtures, indirect lighting, wall lighting or other sources.
Why it matters: Ambient light establishes the general visual environment before task or accent layers are added.
Task Lighting
Task lighting provides additional light where a specific activity takes place.
Examples include:
- kitchen countertops
- desks
- reading chairs
- bathroom mirrors
- work benches
Why it matters: A room can have adequate general lighting while still providing poor visibility at the actual task surface.
Accent Lighting
Accent lighting intentionally draws attention to a particular object, surface or architectural feature.
Examples include:
- artwork
- textured walls
- shelving
- plants
- architectural details
Why it matters: Accent lighting creates hierarchy, contrast and visual interest.
Decorative Lighting
Decorative lighting uses the fixture itself as part of the visual composition of the space.
Examples include chandeliers, sculptural pendants and decorative wall lights.
Why it matters: The fixture contributes to the interior design even when it is switched off.
Layered Lighting
Layered lighting combines several lighting functions rather than asking one fixture type to do everything.
A typical scheme may combine:
- general lighting
- task lighting
- accent lighting
- decorative lighting
Why it matters: Layering allows a room to respond to different activities and moods while improving visual comfort.
Task Plane
The task plane is the surface where a visual activity takes place and where the useful light level is assessed.
Examples include:
- a kitchen countertop
- office desk
- dining table
- work bench
Why it matters: Lighting should be planned according to the surface that needs illumination, not only according to the ceiling layout.
Uniformity
Uniformity describes how evenly light levels are distributed across an area.
Why it matters: Very large differences between bright and dark areas can make some applications visually uncomfortable or difficult to use.
Practical note: Perfect uniformity is not always desirable. Accent and decorative lighting intentionally use contrast, while workplaces may require more controlled uniformity.
Glare
Glare occurs when excessive brightness or strong contrast causes visual discomfort or reduces visibility.
It can come from:
- exposed light sources
- reflections
- poorly aimed spotlights
- excessive luminance within the field of view
Practical note: Shielding, fixture position, beam control and suitable output can all help manage glare.
Lighting Contrast
Lighting contrast is the difference in brightness between adjacent surfaces or objects.
Why it matters: Contrast can create depth and visual hierarchy, but excessive contrast can make a space uncomfortable.
Practical note: Residential and decorative environments often benefit from controlled variation rather than completely uniform illumination.